The School of Biomedical Sciences Wiki - User contributions [en]

Nuclear localisation sequence

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Nuclear localization signals are sorting signals found on [[Protein|protiens]] to be imported into the nucleus. They are, unlike most sorting sequences, not subjected the being cleaved off after importation- due to the fact that many protiens are imported and exported from the nucleus several times. Because of this it is likely that nuclear localisation sequences are likely to form loops or patches rather than being found on a terminus. Nuclear localisation sequences bind to [[Nuclear import receptors]]. Nuclear import receptors to allow for importation of the protien into the [[Nucleus|nucleus]]<ref>Alberts B, Johnson A, Lewis J, Raff M, Roberts K and Walter P. (2007) Molecular Biology of the Cell, 5th edition, New York: Garland Science</ref>.

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Ligand-gated ion channels

2018-10-18T19:29:50Z

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Ligand-gated ion channels act as transmembrane channel that permits [[Ions|ions]] to enter the [[Cell|cell]]. They are triggered by the binding of a [[Chemical messenger|chemical messenger]]. 

The ligand gated ion channels that are considered to be of the most importance by some are found in the [[Nervous system|nervous system]]. The ligands involved are the [[Neurotransmitter|neurotransmitters]] that are released across the [[Synaptic cleft|synaptic cleft.]] These neurotransmitters (often [[Acetylcholine|acetylcholine]]) then bind to their complementary [[Receptors|receptors]] on the channels, causing them to open and allowing the stimulation of an [[Action potential|action potential]] in the post synaptic [[Neuron|neuron]]<ref>Purves D, Augustine GJ, Fitzpatrick D (2001). Neuroscience. (Sunderland: Sinauer Associates) in NCBI &amp;lt;http://www.ncbi.nlm.nih.gov/books/NBK11150/&amp;gt; [accessed 27.11.2014]</ref>. 

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Oligodendrocyte

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The glial cell forming a [[Myelin sheath|myelin sheath]] around axons in the [[Central nervous system|central nervous system]] <ref>Alberts, B. , Johnson, A., Lewis, J., Raff, M., Roberts, K., Walter, P. (2008) Molecular Biology of the Cell, 5th edition, New York: Garland Science.</ref>. However, there are also oligodendrocytes found in the grey matter and they have so far unknown functions possibly similar to astrocytes. There are also gap junctions connecting oligodendrocytes which are composed by connexins. Mutated connexin proteins can cause hypomyelination and various pathologies like leukodystrophies<ref>http://www.networkglia.eu/en/oligodendrocytes</ref>.

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Carboxylic acid (COOH)

2018-10-18T19:27:08Z

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Carboxylic acids are organic compounds which contain a [[Carboxyl group|carboxyl]] group (COOH), they are described by the general formula R-COOH, in which R denotes the remainder of the [[Molecule|molecule]] minus the carboxyl group<ref>McNaught AD (1997). Compendium Of Chemical Terminology. 2nd ed. New York: Blackwell Science. 215.</ref>. The carboxyl group acts as an acid by  dissociating into its conjugate ions of H+ and R-COO-. '''Carboxylic acids in nature''' Carboxylic acids occur extensively in nature, the carboxyl groups and amine groups of different amino acids react together to form peptide bonds and give rise to amino acid polymers otherwise known as proteins.

The carboxylic acid has a formula R-COOH and a structure that involves the [[Carbon|carbon sharing]] a double bond with an [[Oxygen|oxygen]] molecule and another bond joining the [[Carbon|carbon]] group to a OH group made up of [[Oxygen|oxygen]] bound to [[Hydrogen|hydrogen]]. This [[Carboxyl group|carboxyl group]] is always found at the end of the [[Molecule|molecule]]. In [[Water|water]] a carboxylic acid will partially dissociate into carboxylate ions and H+ ions. A carboxylic acid can be obtained by oxidising an [[Aldehyde|aldehyde]].

=== Chemical Synthesis ===

Carboxylic acids can be chemically synthesised from [[Aldehyde|aldehydes]] and [[Alcohol|alcohols]], the [[Oxidation|oxidation]] of an alcohol gives an aldehyde, aldehydes can then be oxidised further to give carboxylic acids. 

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Secondary active transport

2018-10-18T19:22:18Z

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Secondary active transport is a type of [[Active transport|active transport]] that moves two different [[Molecule|molecules]] across a transport membrane. One of the molecules, which may be an [[Ions|ion]], moves across the biological membrane, down its [[Electrochemical gradient|electrochemical gradient]]. This primary molecule is what allows the other molecule, possibly another ion, to move in an uphill direction, against it's concentration gradient. The molecule that moves down its concentration gradient is what drives the movement of the secondary molecule across the membrane. It is because of this that the molecule that travels down its concentration gradient is know as the driving ion.

The difference between secondary active transport and primary active transport is that there is no direct utilisation of an [[ATP|ATP]] molecule in secondary transport. 

There are two types of secondary active transport. One of which, is where the molecules move in the same direction across the transport membrane, this is known as [[Symporter|symport]], involving [[Symporters|symporters]] or exchangers<ref>http://biology.kenyon.edu/HHMI/Biol113/secondary_active_transport.htm</ref>. The other is when the molecules are travelling in the opposite direction to each other, this type of secondary active transport is known as [[Antiporter|antiport]]<ref>http://www.physiologyweb.com/lecture_notes/membrane_transport/secondary_active_transport.html</ref>.

An example of secondary active transport is the movement of [[Glucose|glucose]] in the proximal convoluted tubule.

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Cytoplasmic Vesicles

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There are two types of Membrane-bound cytoplasmic [[Vesicles|vesicles]]: secretory vesicles and storage vesicles.

=== Secretory vesicles ===

Protiens that will be released from the cell are contained in secretory vesicles <ref>Silverthorn,Human Physiology, An integrated Approach, 5th edition (2010) Pearsons Benjamin Cummings, pg69</ref>. 

=== Storage vesicles ===

The content that is held within storage vesicles never depart from the [[Cytoplasm|cytoplasm]]. Two examples of storage vesicles are [[Lysosome|lysosomes]] and [[Peroxisomes|peroxisomes]]. 

Lysosomes use [[Enzymes|enzymes]] which break down old [[Organelles|organelles]] and [[Bacteria|bacteria]], acting as a digestive system for the cell. Most of the broken down molecules are thrown out of the cell, however if still usefull to the cell, they can then be reabsorbed into the [[Cytosol|cytosol]] to be reused. Lysosomal enzymes are very inactive at the normal pH level of 7.0-7.3 <ref>Silverthorn,Human Physiology, An integrated Approach, 5th edition (2010) Pearsons Benjamin Cummings, pg70</ref> in the cytoplasm. They only become activited when the pH is about 4.8-5.0 <ref>Silverthorn,Human Physiology, An integrated Approach, 5th edition (2010) Pearsons Benjamin Cummings, pg70</ref>. This inactivity at a normal PH level is essential, as if the lysosome breaks unintentionally leaks out some of the enzymes they will not react to digest the surrounding material. This stops lysosomes from destroying the cell that there contained in.

Peroxisomes contain a different set of enzymes to lysosomes and are much smaller. The reactions that tke place inside them generate a toxic molecle called [[Hydrogen peroxide|hydrogen peroxide]] (H2O2) which gives them their name. Peroxisomes degrade potentially toxic foreign moelecues aswell as long [[Fatty acid|fatty acid]] chains<ref>Silverthorn,Human Physiology, An integrated Approach, 5th edition (2010) Pearsons Benjamin Cummings, pg70</ref>.

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Conjugative plasmid

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[[Reproduction by Conjugation|Conjugation]] is the process by which a section of [[DNA|DNA]] is tranferred from one living cell (the host) to a second living cell (the recipient). A [[Plasmid|plasmid]] is a small circular piece of DNA which is found free in the cytoplasm of bacteria cells. In most cases bacterial conjugation utilizes the sex pilus which is encoded for within the bacterium such as [[E. coli|E. coli]]. The sex pilus makes the initial contact between the two bacteria cells, depolymerises, and in doing so, pulls the two bacteria cells into very close proximity of one another. Conjugation is usually regulated by the conjugation plasmid; an example of which is the F. plasmid in E. coli. F. plasmids can sometimes carry some bacterial genomic DNA which is called an F' (F Prime) plasmid<ref>Anthony J.F. Griffiths, Susan R. Wessler, Sean B. Carroll, John Doebley, (2012;177), Introduction to Genetic Analysis, 10th Edition, New York, W.H. Freeman, Palgrave, Macmillan</ref>. Non-conjugative plasmids can be transferred during conjugation if they have specific mobilisation (mob) genes <ref>Anthony J.F. Griffiths, Susan R. Wessler, Sean B. Carroll, John Doebley, (2012), Introduction to Genetic Analysis, 10th Edition, New York, W.H. Freeman, Palgrave, Macmillan</ref>. 

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Polypeptide chain

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'''Polypeptide chains''' are [[Polymer|polymers]] of [[Amino acid|amino acids]] joined together with [[Peptide bond|peptide bonds.]] These peptide bonds are formed through [[Condensation Reaction|condensation reactions]] whilst the amino acids are being coded for during [[Translation|translation]]<ref name="null">University of New Mexico. (2002). Available: http://biology.unm.edu/ccouncil/Biology_124/Summaries/T&amp;amp;amp;amp;T.html Last accessed: 27/11/14</ref>.

Whilst in polypeptide chains, amino acids are known as [[Amino acid residues|residues.]] It is conventional to list residues in polypeptide chains starting from the N-terminal: the end with a free [[Amino group|amino group]] as opposed to the C-terminal, which is the end with the free [[Carboxyl group|carboxyl group]]<ref>William Reusch. (2013). Available: http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/protein2.htm Last accessed: 27/11/14</ref>.

Polypeptide chains are the [[Primary structure|primary structure]] of proteins - most natural polypeptide chains contain between 50 and 2000 amino acid residues<ref>J. Berg, J. Tymoczko and L. Stryer. (2012). Biochemistry 7th Ed. Freeman.</ref>.

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Cytokine

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Cytokines are chemical messengers used in many processes in the body. They are particularly useful in the [[Immune system|immune system]] as they promote growth, differentiation and [[Antibody|antibody]] secretion when they bind to antigen-presenting cells via [[Receptors|receptors]]<ref>Berg J, Stryer L, Tymoczko J. (2011) Biochemistry, 7th Edition. International Edition, Basingstoke: Palgrave Macmillan. Chapter 34, page 1038.</ref>. They are recognised by specific cytokine-receptors, that only bind complementary cytokines<ref>Alberts, B.A. and Johnson, A.J. and Lewis, J.L. and Raff, M.R. and Roberts, K.R. and Walter, P.W. 2008. Molecular Biology of the Cell. 5th ed. New York: Garland Science.</ref>. 

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Differentiation

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Differentiation is the process in which unspecialised cells (also known as [[Stem cells|stem cells]]) change to become more specialised, therefore gaining more specific functions. Differentiation is irreversible within mammals, however it is possible to artificially transform somatic cells into induced [[Induced Pluripotent stem cell|pluripotent stem cells]] by changing the gene expression of the somatic cell<ref>Gurdon JB, From nuclear transfer to nuclear reprogramming: the reversal of cell differentiation.Annu Rev Cell Dev Biol. 2006;22:1-22.</ref>. Differentiation plays a critical role in development as this is how a single [[Pluripotent stem cell|pluripotent]] blastocyst can turn into every cell type in the body. Differentiation is controlled chemically with different growth factors signalling the stem cell to specialise into different cell types.

 

 

 

 

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Bronchioles

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Bronchioles are a feature of the respiratory system and branch from the [[Bronchi|Bronchi]], they are the smallest of the airways.  [[Alveoli|Alveoli]] are found at the end of the bronchioles (this is where the gas exchange occurs). 

=== Structure ===

Larger bronchioles have ciliated cells lining the [[Lumen|lumen]]. However, in smaller bronchioles the [[Epithelium]] is not lined with ciliated [[Cells|cells]]<ref>University of Leeds Faculty of Biological Sciences, 2003. The Histology Guide: Bronchioles. Available at: http://www.histology.leeds.ac.uk/respiratory/conducting.php (Last accessed: 22.10.2015)</ref>. 

=== Infection ===

The bronchioles are subject to many infections and diseases including Bronchiolitis obliterans-organizing pneumonia (BOOP) <ref>Pardo J, Panizo A, Sola I, Queipo F, Martinez-Peñuela A, Carias R.. (2013). Prognostic value of clinical, morphologic, and immunohistochemical factors in patients with bronchiolitis obliterans-organizing pneumonia.. Human pathology. 44 (5), 718-24</ref>. 

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Anabolic steroids

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An anabolic [[Steroid|steroid]] is a compound belonging to the [[Androgen|androgen]] family that leads to the development of [[Muscle|muscle]] mass. In humans, [[Testosterone|testosterone]] is the most common anabolic steroid. Testosterone is produced in the [[Testes|testes]] of males, and in small amounts in the [[Ovaries|ovaries]] of females.

Due to it's properties as a muscle builder, synthetic anabolic steroids are sometimes taken by athletes who are aiming for [[Muscular hypertrophy|muscular hypertrophy]]. Even in small doses this can have side effects which differ between males and females. Side effects seen in males include; [[Testicular atrophy|testicular atrophy]], hair growth, breast development, infertility, and mood swings. Females, on the other hand, can suffer from side effects such as, loss of breasts, swelling of the clitoris, a deepend voice, and facial hair growth. There is an increased risk of some medical conditions too. These include; [[Liver|liver]] or [[Kidneys|kidney]] tumours, [[Hypertension|hypertension]], blood clots and high [[Cholesterol|cholesterol]]<ref>Anabolic steroid misuse http://www.nhs.uk/conditions/anabolic-steroid-abuse/Pages/Introduction.aspx Last reviewed 08/11/2013</ref>. As well as this, the body often stops secreting as much testosterone naturally<ref>Berg J, Tymoczko J, Stryer L. (2012) Biochemistry, Seventh edition, New York: WH Freeman</ref>.

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ATP-ase

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[[Enzyme|Enzyme]] which catalyses the hydrolsis of ATP, to ADP and an inorganic phosphate<ref>Alberts,Molecular Biology of the cell 5th edition,page 80F</ref>  A example of a ATP-ase is the Ca2+ pump, this is a P type transport ATPase which is located in the SR of [[Skeletal Muscle Cell|skeletal muscle cells]]<ref>Alberts,Molecular Biology of the cell 5th edition 2008,page 660</ref>.

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A b toxin

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A B toxins are toxins with 2 subunits, A and B. A B toxins are normally secreted by pathogenic bacteria. the A subunit is known as the 'active' subunit, because this subunit uses enzymes to interfere with proteins in the host cell. This interference can cause proteins to become inactive. The B subunit is known as the 'binding' subunit, because this subunit binds to receptors on the host cell<ref name="as stated by Kaiser (2014)">A B toxins are toxins with 2 subunits, A and B. A B toxins are normally secreted by pathogenic bacteria. The A subunit is known as the 'active' subunit, because this subunit uses enzymes to interfere with proteins in the host cell. this interference can cause proteins to become inactive. The B subunit is known as the 'binding' subunit, because this subunit binds to receptors on the host cell</ref>.

 

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Gary E. Kaiser (2014), Doc Kaisers Microbiology Home Page. Avalible from; http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/bacpath/abtox.html [Accessed: May 2014]

Parasympathetic nervous system

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The Parasympathetic Nervous System is a subdivsion of the [[Autonomic Nervous System|Autonomic Nervous System]]. This system is termed the "rest and digest" as it co-oridnate the functions of organs involved in these processes autonomically. The PNS works in tandem with the [[Sympathetic nervous system|Sympathetic nervous system]] and normally the PNS will produce the opposite affect on an organ to what the SNS will. For example, the SNS will cause a reduction in salivary secreteion and production while the PNS will increase this<ref>Rhoades, R Pflanzer, R (2003). Human Physiology. 4th ed. London: Thomas Brook/Cole. P340-341.</ref>. 

This is all mediated by varying different neurotansmitters. The primary transmitters used in the Parasympathic nervous system is [[Acetylcholine|Acetylcholine]]. This is for both pre and post ganglionic cells. This is also the same for the the receptor which would be cholinergic receptors. These can be subdived into two groups; Nicotinic and Muscarinic.

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Α-Ketoglutarate

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Alpha Ketoglutarate is a Keto acid produced by the deamination of [[Glutamate|Glutamate]], a reaction that occurs during the [[Krebs cycle|Krebs cycle]]. Alpha Ketoglutarate is an important intermediate in the Krebs Cycle and is produced in the cycle just prior to [[Succinyl CoA|Succinyl CoA]]. A key function of Alpha Ketoglutarate is to combine with Nitrogen, eliminating the prospect of [[Nitrogen|nitrogen]] overload. Through this ability, Alpha Ketoglutarate has an important function to detoxify [[Ammonia|ammonia]] present in the [[Brain|brain]]. Alpha Ketoglutarate also functions as an antioxidant and decreases levels of [[Hydrogen peroxide|hydrogen peroxide]] in the body<ref>Long, L; Halliwell, B (2011). "Artefacts in cell culture: α-Ketoglutarate can scavenge hydrogen peroxide generated by ascorbate and epigallocatechin gallate in cell culture media.". Biochemical and biophysical research communications 406 (1): 20–24. doi:10.1016/j.bbrc.2011.01.091.</ref>.

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Glucose

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Glucose is a [[Monosaccharide|monosaccharide]] with the chemical formula of C6H12O6. It is involved in many biological processes including [[Glycolysis|glycolysis]]. [[Glycolysis|Glycolysis]] involves the conversion of [[Glucose|glucose]], to [[Pyruvate|pyruvate]]. This process is fundamental to [[Respiration|respiration]]. Glucose can form a [[Glycosdic bond|glycosidic bond]] with another glucose to form a [[Disaccharide|disaccharide]] called [[Maltose|maltose]] through a condensation reaction. Glucose monomers can be joined by α-1,4- [[Glycosidic bond|glycosidic bond]] to form a polysaccharide molecule known as [[Starch|starch]]. 

In open chain [[Glucose|glucose]] Carbon 1 (the [[Carbonyl group|carbonyl]] carbon) is not [[Chiral centre|chirally]] active. However in the ring structure it becomes assymetric, allowing it to form two ring structures: [[Α-D-glucopyranose|α-D-glucopyranose]] and [[Β-D-glucopyranose|β-D-glucopyranose]]<ref>Berg J., Tymoczko J and Stryer L. (2012) Biochemistry, 7th edition, New York: WH Freeman. pg 333</ref>. 

[[Image:D-glucose.jpg|D-glucose forming alpha and beta rings.]]

Taken from: [http://www.ncbi.nlm.nih.gov/books/NBK22547/ http://www.ncbi.nlm.nih.gov/books/NBK22547/]<ref>http://www.ncbi.nlm.nih.gov/books/NBK22547/</ref> 

The main family of transporters are known as the GLUT family with 5 known variants all with different properties and found in different tissues.

*[[GLUT1|GLUT1]]
*[[GLUT2|GLUT2]]
*[[GLUT3|GLUT3]]
*[[Glut 4|GLUT4]]
*[[GLUT5|GLUT5]]

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Trypsin

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Trypsin is found in the digestive system, it's a protease [[Enzyme|enzyme]] produced in the [[Pancreas|pancreas]]. Trypsin is an [[Endopeptidase|endopeptidase]]. This means that it cleaves [[Amino acids|amino acids]] in the middle of the [[Polypeptide chain|polypeptide chain]] as opposed to cleaving the amino acids on the end of the polypeptide chain. It is a hydrolytic endopeptidase as it uses [[Hydrolysis|hydrolysis]] as the mechanism to break down polypeptides<ref name="null">Biologyguide.net, (2015). Digestive System. [online] Available at: http://www.biologyguide.net/bya7/bya7-16-4.htm [Accessed 2 Dec. 2015].</ref>. Trypsin is used in some proteomic investigations where the enzyme is used to cleave the peptide in question at specific points, at the C- terminal to Arginine and Lysine residues<ref>Olsen J. Trypsin Cleaves Exclusively C-terminal to Arginine and Lysine Residues. Molecular &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp; Cellular Proteomics. 2004;3(6):608-614.</ref>. The resulting peptides can be recorded in a database, this data can be used to identify this protein in future studies<ref>What is Proteomics? [Internet]. Office of Cancer Clinical Proteomics Research - National Cancer Institute. 2016 [cited 17 October 2016]. Available from: http://proteomics.cancer.gov/whatisproteomics</ref>.

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Gerstmann-Straussler-Scheinker syndrome

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Gerstmann-Straussler-Scheinker (GSS) syndrome is a neurodegenerative disorder<ref>1. National Institute of Neurological Disorders and Stroke (NINDS), Gerstmann-Straussler-Scheinker Disease Information Page, (2007),[Online], Available at: http://www.ninds.nih.gov/disorders/gss/gss.htm. Accessed 3/21/2008, (Last Accessed: 26/11/14)</ref> affecting the [[Brain|brain]]. This leads to conditions such as ataxia and dementia, which includes common symptoms of memory loss and the loss of balance and coordination, respectively. The disease itself is almost always inherited and is very rare; only a few known cases are reported around the world, running down through families<ref>De Michele G, Pocchiari M, Petraroli R, et al., (August 2003), "Variable phenotype in a P102L Gerstmann–Sträussler–Scheinker Italian family", Can J Neurol Sci 30 (3): 233–6. PMID 12945948</ref> due to inheritance. Onset of the disease usually occurs between the ages of 35 and 55. GSS syndrome belongs to a family of human and animal diseases known as the transmissible spongiform encephalopathies (TSEs) or [[Prion|prion]] diseases<ref>K Hsiao, C Cass, GD Schellenberg, A prion protein variant in a family with the telencephalic form of Gerstmann–Sträussler–Scheinker syndrome, Neurology, 41 (1991), pp. 681–684</ref>. 

=== Causes ===

GSS is one of few diseases that are caused by the transformation of prion proteins; often due to small changes in its [[Amino acid|amino acid]] sequence at a particular [[Codon|codon]].  A change in the amino acid sequence from [[Proline|Proline]] (P) to [[Leucine|leucine]] (L) on [[Codon|codon]] 102 found in [[Chromosome 20|chromosome 20]]<ref>L Goldfarb, P Brown, A Vrbovská, An insert mutation in the chromosome 20 amyloid precursor gene in a Gerstmann–Sträussler–Scheinker family, J Neurol Sci, 111 (1992), pp. 189–194</ref>, is observed in the prion protein gene (PRNP) of most affected individuals. From current knowledge, this genetic change is usually required for the development of GSS. Genetic testing allows for the [[Diagnosis|diagnosis]] of this underlying genetic mutation. This involves a [[Blood|blood]] and [[DNA|DNA]] sample from a potential patient and examining it in order to attempt to detect this mutated gene at certain codons. If the genetic mutation is present, the patient will eventually be afflicted by GSS, and, due to the genetic or inheritance-based nature of the disease, the offspring of the patient have a much higher risk of inheriting the Proline to Leucine mutation, thus contracting GSS. 

=== Treatment ===

There is no known cure available GSS, and there are no known treatments to slow the progression of the disease. However, therapies and medication are aimed at treating or slowing down and alleviating the symptoms, which will hopefully lead to an increased quality of life for the patient. 

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Hutchinson-Gilford Progeria Syndrome

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== Brief Background ==

This is a rare disorder that is characterised by premature aging <ref>Pollex,R.L.,Hegele,R,A."Hutchinson–Gilford progeria syndrome"Clinical GeneticsfckLRVolume 66, Issue 5, pages 375–381, November 2004</ref>. The syndrome was discovered by Jonathan Hutchinson and Hastings Gilford <ref>Progeria Research Foundation (2011). “About Progeria” (http://www.progeriaresearch.org/about_progeria.html), [last viewed: 11th November, 2011]</ref> and it occurs in 1 in 8 million people.

== Cause ==

It is due to a completely random point mutation at the 1824th position of the [[Lamin A|Lamin A]] protein leading to the substitution of thymine with [[Cytosine|cytosine]] <ref>Brown, W.T.,Kliegman, R.M., Behrman, R.E., Jenson, H.B., Stanton, B.F., eds. (2007) “Progeria”. Nelson Textbook of Pediatrics 18th Ed. Philadelphia, Pa: Saunders Elsevier; chap 90</ref>. It is said to be completely random as there is no specific tribe or race associated with it. It has been discovered in patients across the globe.  Although their is no current evidence that the syndrome can be inherited their is a family in India that all the children have the syndrome.

== Symptoms ==

#[[Alopecia|Alopecia]]
#Delayed tooth formation
#[[Scleroderma|Scleroderma]]
#[[Macrocephaly|Macrocephaly]]
#Prominent scalp veins
#Bulging eyes
#High pitched voice
#Growth failure
#Loss of muscles and body fat
#Progressive cardiovascular diseases
#Progressive [[Atherosclerosis|atherosclerosis]]
#Death <ref>Gordon, L.B., Brown T.W., Collins, F.S. (2003). “Hutchinson-Gilford Progeria Syndrome”. Gene Reviews (http://www.ncbi.nlm.nih.gov/books/NBK1121/), [last viewed: 05th April, 2011]</ref> 

== Treament ==

Drugs - [[Pravastatin|pravastatin]] and [[Zoledronate|zoledronate]] 

Pravastin helps to prevent cardiovascular related diseases while zoledronate helps to prevent skeletal fractures in patients<ref>Clinical trials. (2010) http://clinicaltrials.gov/ct2/show/NCT00731016</ref>.

== Reference list ==

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The Sliding Filament Theory

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The sliding of [[Myosin|myosin]] and [[Actin|actin filaments]] causes muscles to contract. There are many forms of muscle contraction including contraction of the skeletal [[Muscle|muscle]], the [[Heart|heart]] and gut peristalsis<ref>Alberts et al, Molecular Biology of the Cell, 5th edition:1026</ref> all of which require the well regulated movement of the [[ATP|ATP]]-dependent sliding filaments. Each [[Sarcomere|sarcomere]] is made up of a highly organised sequence of thick and thin filaments. The thin filaments are mainly made up of [[Actin|actin]] along with associated [[Protein|proteins]] <ref>Alberts et al, Molecular Biology of the Cell, 5th edition:1026</ref>. These filaments are all attached by their ends to a structure called a Z disc, the other end reaches parallel into the structure overlapping the thick filaments which are made up of [[Myosin|myosin]], each filament is evenly spaced between the other<ref>Alberts et al, Molecular Biology of the Cell, 5th edition:1026</ref>. Sarcomere shortening is not caused by the contraction or shortening of the actual filaments but by the sliding of the myosin filaments past the actin filaments<ref>Bowness et al, CGP, A2 Level Biology Revision guide:62</ref>.

[[Image:Sliding filament theory.jpg]] 

 

Figure taken from  http://www.ncbi.nlm.nih.gov/books/NBK9961/

=== Sliding mechanism   ===

As a result of depolarisation of [[T-tubules|T-tubule]] membrane caused by [[Acetylcholine|acetylcholine]] binding to receptor on the motor end plate Ca2+ [[Ions|ions]] are released into the cytosol<ref>B. Alberts, Molecular Biology if the Cell, Garland Science, 5th Edition ,2008</ref>. Then they bind to one of the accessory [[Protein|proteins]] [[Troponin|troponin]]<ref>B.Alberts, Molecular Biology of the Cell, Garland Science, 5th edition, 2008</ref>.Troponin is a composed of 3 polypeptides ([[Troponin T|troponin T]], [[Troponin I|troponin I]] and [[Troponin C|troponin C]]). When the muscle is at rest troponin is bound to actin in such a way that troponin I and troponin T pull the other accessory protein [[Tropomyosin|tropomyosin]] out of its place so it blocks the [[Myosin|myosin]] binding site on the [[Actin|actin]]. During contraction 4 Ca2+ ions bind to the troponin C subunit forcing the troponin I to release its hold of actin thus allowing the tropomiosin to move back to its place and open the myosin binding site so the muscle can contract by binding of myosin heads to actin and then twisting to make the [[Sarcomere|sarcomere]] shorter<ref>B. Alberts, Molecular Biology of the Cell, Garland Science, 5th edition , 2008</ref>.

=== References ===

<references />

Uniport carrier

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A uniport carrier is a membrane transport protein that moves only one kind of [[Molecule|molecule]]. It does not generally require energy as it follows the concentration gradient of the molecule in question. 

=== Examples ===

An example of a uniporter is the [[Glucose transporter|glucose transporter]] (GLUT) in found in [[Erythrocyte|erythrocytes]] (reffered to as [[GLUT1|GLUT1]] to separate from other mamalian glucose transporters). This allows glucose to enter the cell via [[Facilitated diffusion|facilitated diffusion]] and it does so at approximately 50,000times the rate that it would via [[Simple diffusion|simple diffusion]]<ref>Becker's World of the Cell, Eighth Edition (J. Hardin, G.Bertoni, L.J. Kleinsmith) 2012 San Francisco:Pearson Page 203</ref>. This process is not active (meaning it does not require an energy input). Once inside the cell the glucose is quickly [[Phosphorylation|phosphorylated]] to glucose-6-phosphate by the [[Enzyme|enzyme]], hexokinase, to prevent it from diffusing out. This is also the first step in [[Glycolysis|glycolysis]]<ref>Becker's World of the Cell, Eighth Edition (J. Hardin, G.Bertoni, L.J. Kleinsmith) 2012 San Francisco:Pearson Page 204</ref>. 

=== See Also ===

[[Symporter|Symporter]]

[[Antiporter|Antiporter]] 

=== References ===

<references />

Protein

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A protein is a biological [[Polymer|polymer]] which is made up of structures called [[Amino acid|amino acids]]. The [[Amino acids|amino acids]] are joined together with a [[Peptide bond|peptide bond]] to form a [[Polypeptide|polypeptide]] chain. The [[Peptide bond|peptide bond]] is formed by joining the ɑ-carboxyl group of an [[Amino acid|amino acid to]] the ɑ-amino group of another [[Amino acid|amino acid]]<ref name="null">Berg et al., (2006) Biochemistry, 6th edition, New York. Pg 34</ref>. A protein can be made up of a single polypeptide chain or multiple [[Polypeptides|polypeptides]] linked together. There are three types of proteins: [[Fibrous|fibrous]], [[Globular protein|globular]] and [[Membrane protein|membrane proteins]]. Examples of proteins include [[Enzyme|enzymes]], [[Receptor|receptors]] and [[Hormone|hormones.]]  They are found in every form of life from [[Virus|viruses]] to [[Bacteria|bacteria]]; [[Yeast|yeasts]] to [[Humans|humans]]. One important technique used to analyse proteins is [[SDS polyacrylamide-gel electrophoresis|SDS polyacrylamide-gel electrophoresis]] ([[SDS polyacrylamide-gel electrophoresis|SDS-PAGE]]).  Proteins can make up to 50% of the weight of a cell, and up to 25% of a humans dry bodyweight.

== Structure ==

A protein has several 'layers' of structure <ref>Elliott.W.H, Elliott.D.C (1997) Biochemistry and Molecular Biology. New York, United States: Oxford University Press.pp.47-49.ISBN 0199271992</ref>. The function of the protein is determined by its structure, therefore each layer is dependent on the next<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>.

=== Primary Structure ===

The [[Primary structure|primary structure]] is the specific sequence of [[Amino acids|amino acids]] joined together by [[Peptide bonds|peptide bonds in]] a [[Polypeptide|polypeptide]] chain. There are 20 different [[Amino acids|amino acids]] found in nature. The sequence of amino acids is determined by the [[DNA|DNA]] sequence that encodes for that particular protein. This is know as the [[Gene|gene]].  

=== Secondary Structure ===

[[Secondary structure|Secondary structure]] is the first level of protein folding. The two main folding structures of a protein are the [[Alpha-helix|alpha-helix]] or the [[Beta-sheet|beta-sheet]] depending on the sequence of [[Amino acids|amino acids]]. This, in turn, allows the protein to have a [[Hydrophobic|hydrophobic]] core and a [[Hydrophilic|hydrophilic]] surface. The secondary structure is stabilised by [[Hydrogen bonds|hydrogen bonds]] between the C=O and H-N groups<ref>Clark, J (2004) The Structure of Proteins. [Internet], Available from: http://www.chemguide.co.uk/organicprops/aminoacids/proteinstruct.html;[Accessed 20 October 2015].</ref> for the peptide backbone.

=== Tertiary Structure ===

[[Tertiary structure|Tertiary structure]] relates to the protein function.  If the [[Tertiary structure|tertiary structure]] is altered, then the protein is unlikely to function properly. [[Tertiary structure|Tertiary structure]] is held together by either [[Hydrogen bonds|hydrogen bonds]] or [[Disulphide bridges|disulphide bridges]] depending on the [[Amino acids|amio acids]] present. Disulphide bridges are formed between the amino acid [[Cysteine|Cysteine]] <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>. 

=== Quaternary Structure ===

One or more tertiary structure of proteins linked together build up a [[Quaternary structure|quaternary structure]]. Quaternary structure can also refer to proteins with an inorganic prosthetic group attached, an example being [[Haemoglobin|haemoglobin]]: a tetramer consisting of four myoglobin subunits and an iron-containing [[Haem group|haem group]]. Two of the subunits are alpha, and two are beta <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>. 

== Functions of Proteins ==

Proteins makeup 50% of each cell and have both structural and functional importance. Proteins transport numerous different particles from macromolecules to electrons. [[Enzymes|Enzymes]] are globular proteins that act as biological [[Catalysts|catalysts]], and collagen is a fibrous protein which provides strength and structural support in many tissues. Proteins in the form of hormones transmit information between specific cells.

Structural proteins include:

*the silk-[[Beta pleated sheet|beta pleated sheet]] which has Alanine and Glycine residues forming a rigid, stable structure. Spiders can make silk and in this type of silk the rigid sections alternate with stretchy ones in order to make the structure both strong and elastic.
*[[Keratin|A-Keratin]] which is present in hair, nails, and wool (among others). This structure is usually stretchy and flexible, however, when many disulphide bridges are present (for example, in hooves and nails) the structure remains rigid and loses flexibility. 
*[[Collagen|Collagen]], consisting of a coil of three strands of glycine-proline-proline which is 100 strands long. This is the most abundant protein in mammals.

Enzymes work by binding substrate at their active sites, which is a specific region dependant on amino acid sequence forming an enzyme-substrate complex. This causes a conformational change in the shape of the enzyme which encourages catalysis by putting strain on the bonds in the substrate (and/or by other means). 

A group of protein structures called motor proteins are responsible for activities such as [[Muscle contraction|muscle contraction]], cell movement, migration of [[Chromosomes]] during [[Mitosis]] and the direction of [[Organelles|organelles]]. There are two different types of [[Microtubules|microtubule]] motor proteins known as [[Kinesin|kinesins]] and [[Dynein|dyneins]]. Kinesins facilitate the carrying of organelles toward the positive end of the [[Microtubule|microtubule]] and dyneins are important of the movement of [[Cilia|cilia]] or [[Flagella|flagella]] in organisms <ref>Alberts.B et al, (Fifth Edition); Molecular Biology of the Cell; Taylor and Francis Group, pp 1014-1015</ref>. 

=== Synthesis of Proteins  ===

Protein synthesis can be divided into two sections, transcription and translation. In transcription DNA is used to code for the protein, it start at a [[Promotor gene|promotor gene]] at the 5' end one of the two DNA strands, here [[RNA polymerase|RNA polymerase]], which does not require primers, moves down the strand and forms a complementary sequences of [[Pre-mRNA|pre-mRNA]]. (Thymine [[DNA bases|base]] is replaced with Uracil)  This pre-mRNA contains non-coding [[Introns|introns]] and coding [[Exons|exon]], due to this the pre-mRNA is spliced to remove the introns leaving only the coding sequences of mRNA. This mRNA is used to code for the [[Protein sequence|protein sequence]].   

In translation the [[MRNA|mRNA]] binds to a ribosome, this ribosome then moves down the mRNA from the 5' to 3' end. [[TRNA|tRNA has]] an anticodon sequence with three bases on it that are complementary to a [[Codon|codon]] on the mRNA, it also carries a specific amino acid. Here the RNA carries this [[Amino acid|amino acid]] to the [[Ribosome|ribosome]] and its complementary triplet code on the mRNA. [[Peptide bonds|Peptide bonds]] are formed between amino acids next to each other ( when their two triplet codes are next to each other) <ref>Lesk A.M. Introduction to Protein Science, architecture, function and genomics. 3rd ed. Oxford. Oxford University Press. 2015</ref>. 
This forms the [[Primary structure|primary structure]] of proteins which is the amino acid sequence. 

== See also ==

*[[Amino acid|Amino acid]] 

== References ==

<references />

Antibody

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[[Image:Antibody.jpg|right|Janeway CA Jr, Travers P, Walport M, et al.(2001) Immunobiology: The Immune System in Health and Disease. 5th edition,New York, Garland Science, Figure 3.1.]]Antibodies are large [[Glycoproteins|glycoproteins]] secreted by B lymphocytes to help protect the body against [[Infection|infection]]. They bind with a high degree of specificity to molecular structures ([[Antigens|antigens]]) on infectious agents. This can lead to enhanced killing of [[Microbes|microbes]] by [[Phagocytes|phagocytes]] or [[Complement|complement]] <ref>Janeway CA Jr, Travers P, Walport M, et al.(2001) Immunobiology: The Immune System in Health and Disease. 5th edition,New York, Garland Science, Figure 3.1.</ref>.

They can be segregated into 5 classes of Immunoglobulin; [[IgG|IgG]], [[IgM|IgM]], [[IgE|IgE]], [[IgA|IgA]] and [[IgD|IgD]]; their class is determined by the type of heavy chain in the antibody with corresponding lower-case Greek letters (γ, μ, ε, α,and δ respectively). Each of them has a different distribution in the body. [[IgM|IgM]] and [[IgA|IgA]] are multimeric. The other three are [[Monomeric|monomeric]] antibodies. [[IgA|IgA]] exist as both multimeric and [[Monomeric antibody|monomeric antibody]] in different tissues of the body. The classes differ in their structure and function.

=== Structure ===

Antibody [[Molecule|molecules]] are in the shape of a Y, and all consist of three parts that are connected together by [[Disulphide bond|disulphide bonds]] in order to form this Y shape. Antibodies are also made up of a two [[Polypeptide|polypeptide]] chains; a heavy chain and a light chain. All [[Immunoglobulin|immunoglobulin]] molecules contain heavy and light chains that are identical, giving rise to two identical [[Antigen|antigen]]-binding sites.The light chains of the immunoglobulin molecule are categorised as lambda or kappa. Any of the light chains can be associated with any heavy chains but one immunoglobulin molecule can only have either kappa or lambda chain, not both<ref>Peter Wood.Understanding Immunology. Third edition. Pearson Education Limited, England( 2011</ref>.The synthesis of either kappa or lambda light chains is known as isotype exlusion which occurs as a consequence of allelic exlusion<ref>Janeway C,Immunobiology: The immune System in Health and Disease 2001, 5th Edition,New York: Garland Science,Chapter 5 Page 7-10.</ref>.The stem of the Y is a constant region composed of only heavy chains. The ends of the arms of the Y form variable regions composed of heavy and light chains. The constant regions can be used to distinguish between the 5 classes of immunoglobulins while the variable regions 'vary' between different antibody molecules. This variable region binds to the specific antigens and is made up of six hypervariable loops. Three of these come from VL (variable light-chain) and three from the VH (variable heavy- chain) regions. Between these regions exists more stable FR (framework regions) which make up the rest of the variable region. They provide stability to the antibody and when folded into secondary structure provide a scaffold to anchor the HV regions in place<ref>Klaus D. Elgert Immunology: Understanding the Immune System 2nd edition (2009) New Jersey; John Wiley and Sons Inc</ref>. Specificity depends on the amino acid sequence in the hypervariable region. In contrast, the CH (constant heavy-chain) is used to interact with effector cells and complement.

=== Antigen-binding and recognition ===

The VL and VH domains are highly variable in their amino acid sequence forming a unique antigen-binding site or paratope<ref>Male D, Brostoff J, Roth DB, Roitt IM. Immunology, 8th edn. London Elsevier Health Sciences UK; 2013: p9.</ref>.The hypervariable regions that form the antigen-binding site are therefore also called complementarity-determining regions (CDRs)<ref>Abbas AK, Lichtman AH, Pillai S. Cellular and Molecular Immunology, 8th edn. Philadelphia: Elsevier Saunders; 2015: p88-94.</ref>. Analysis of the three-dimensional structure of Abs performed by X-ray crystallographic techniques proposes that the mechanism for antigen-binding is the induced fit mechanism at the CDR.

The hinge region is a segment of the CH chains. Since Ags are able to have epitopes at non-adjacent sites, the hinge region is critical for the flexibility of the Ab, thus allowing the two antigen-binding sites to act independently<ref>Newsholme EA, Leech TR. Functional Biochemistry in Health and Disease. Chichester, UK: Wiley-Blackwell; 2010: p383-386.</ref>.

Through [[Amino acid|amino acid]] sequence analysis, homology regions were found which are referred to as 'homology domains'. The L chain comprises 2 domains and the H chain can have either 4 or 5 domains. Each domain is around 110 [[Amino acids|amino acids]] in length, comprised of two beta sheets, linked by a [[Disulphide bond|disulphide bridge]]. It is worth noting domains are also paired - folded units within the protein.

Antigen-binding sites bind to [[Epitopes|epitopes]] on the antigen. The [[Epitopes|epitope]] can be linear ([[Continuous antigen|continuous]]) or conformational ([[Discontinuous antigen|discontinuous]])

=== References ===

<references />

Secondary structure

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Hydrogen bond formation causes the protein secondary structure to be stabilise.There are two main forms of protein secondary structure, the [[Alpha-helix|alpha helix ]] and the [[Beta sheet|beta sheet]], however other forms such as the beta turn and the omega loop are known to exist <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>.

== Alpha helix ==

The structure of the alpha helix, first predicted by Pauling and Corey in 1951 <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>, consists of a coiled helical structure held together by [[Hydrogen bonds|hydrogen bonds ]]<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. The helix can be left or right handed, coiling in an anticlockwise or clockwise direction respectively; however the right handed configuration is more energetically favourable due the fact that the side chains of the peptide backbone do not interfere with each other as much <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. The hydrogen bonds that stabilise the structure are formed between the carbonyl oxygen (CO group) of the nth residue and the amide hydrogen (NH group) of the n+4th residue <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. A turn of the helix consists of 3.6 amino acid residues and the rise from one residue to the next is approximately 1.5A<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. 

When it was discovered, the alpha helix was found in the protein α-keratin, which is abundant in skin and its derivatives- hair, nails and horns. Short regions of alpha helix are mainly present in proteins that are embedded in cell membranes such as transport proteins and receptors<ref> Alberts B., Bray D., Hopkin K., Johnson A., Lewis J., Roff M., Roberts K., Walter P. (2013), Essentials Cell Biology, 4th edition, New York: Garland Science. page 132 </ref>.

Sometimes two or three alpha helices will wrap around one another to form a particularly stable structure known as a coiled-coil. This structure forms when the alpha helices have most of their nonpolar side chains on one side so that they can twist around each other with these side chains facing inward- minimizing their contact with the aqueous cytosol. Long, rodlike coiled-coils form the structural framework for many elongated proteins. Examples include α-keratin, which forms the intracellular fibres that reinforce the outer layer of the skin, and [[Myosin]], the motor protein responsible for muscle contraction<ref>Alberts B., Bray D., Hopkin K., Johnson A., Lewis J., Roff M., Roberts K., Walter P. (2013), Essentials Cell Biology, 4th edition, New York: Garland Science. page 133-134 </ref>.

== Beta sheet ==

The beta sheet is the other main secondary structure of proteins, beta sheets are made up of two or more peptide chains called beta strands <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. Hydrogen bonds are formed between two adjacent beta strands <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. The side chains of the amino acid residues point out perpendicularly in opposite directions (up and down) to the plain of the peptide backbone of the beta strands<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. 

There are two types of beta sheets, anti-parallel and parallel. Anti parallel beta sheets are formed from adjacent beta strands running in an alternating configurations, if beta strand n runs from the N terminus to the C terminus the beta strand n+1 runs from the C terminus to the N terminus and the strands of the beta sheet alternate in that manner <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. The hydrogen bonds are formed between the amide hydrogen (NH group) and the carbonyl oxygen (CO group) of one beta strand and the carbonyl oxygen (CO group) and the amide hydrogen (NH group) of the adjacent strand respectively <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. The hydrogen bonds in an anti-parallel beta sheet are short and straight making them strong <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. The parallel beta sheets are formed from adjacent beta strands running in the same configuration, if beta strand n runs from the N terminus to the C terminus then beta strand n+1 also runs from the N terminus to the C terminus <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. The hydrogen bonds are formed between the amide hydrogen (NH group) of an amino acid residue on beta strand n and the carbonyl oxygen (CO group) of the adjacent strand beta strand, n+1 <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. The carbonyl oxygen (CO group) of beta strand n forms hydrogen bonds with the amide hydrogen (NH group) of the amino acid residue two residues further down on the adjacent strand<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>. The hydrogen bonds in parallel beta strands are long and angled making them weaker than those found in anti-parallel beta sheet <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. page 40-42</ref>.

== References ==

<references />

Chemotroph

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An organism whose primary energy source is from chemical reactions. They obtain their energy by oxidising [[Organic_compound|organic]] or [[inorganic compound|inorganic compounds]]. They can also be known as [[chemoautotrophs|chemoautotrophs]] and chemoheterotrophs<ref>Biology-online.org [internet] [cited 2015 Dec 2] Available from: http://www.biology-online.org/dictionary/Chemotroph</ref>



=== References ===

<references />.

Calcium ions

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=== Importance of Calcium Ions ===

==== Bone Mineralization  ====

Bone rigidity is partially due to a salt in it's osteoid matrix which consists of [[calcium|calcium]] and phosphate ions. If the ion concentrations are above the threshold value then bone mineralization will occur. In order to maintain the ion concentrations:

#[[Osteocalcin|Osteocalcin]], a [[glycoprotein|glycoprotein]], binds to calcium ions within the osteoid.
#Alkalin phosphatase, an [[enzyme|enzyme]], increases the calcium and phosphate ion concentration.
#Matrix vesicles found in the osteoblasts contain alkalin phosphatase. 

If there is a calcium deficiency in the blood, mineralization does not complete causing a disease called "osteomalacia" . This causes the bone to soften and become more vulnerable to damage leading to rickets or other bone deformaties <ref>Lowe, J. and Stevens, A. (2005:256) Human Histology, 3rd edition, Maryland: Elsevier Mosby.</ref>. 

==== Parathyroid Hormone  ====

Parathyroid glands, located in the region of the neck, release the hormone parathormone which maintains the calcium concentration in the blood. In order to increase the concentration it "mobilizes the calcium stored in mineralized bone"<ref>Lowe, J. and Stevens, A. (2005:279) Human Histology, 3rd edition, Maryland: Elsevier Mosby.</ref> by "stimulating osteoclastic activity"<ref>Lowe, J. and Stevens, A. (2005:261) Human Histology, 3rd edition, Maryland: Elsevier Mosby.</ref>. This works by reducing the loss of calcium ions in the kidney and by increasing the reabsorption of the ion into the small intestine.  

When calcium ions levels are persistently low the constant activity of [[parathyroid glands|parathyroid glands]] cause them to swell. This swelling is called parathyroid hyperlasia. Additionally, an over-secretion of parathormone brings about excessive damage to the bone and a surplus of calcium in the blood.  

==== Muscle Contraction  ====

===== Skeletal Muscle Cells  =====

During muscle contraction high concentrations of calcium are required to displace [[Troponin|troponin]] and reveal the active site at which myosin binds to for the power stroke. Calcium is released from the sarcoplasmic reticulum through calcium ion channels when the membrane of the T-tubular system is excited. It binds to [[Troponin C|Troponin C]] causing it to conform, hence permitting the [[Myosin|myosin]] head to latch onto the [[Actin|actin]] filament, onsetting muscle contraction<ref>Lowe, J. and Stevens, A. (2005:75) Human Histology, 3rd edition, Maryland: Elsevier Mosby.</ref>. 

===== Cardiac Muscle  =====

Similarly to skeletal muscles, the contraction of cardiac muscles is regulated by the concentration of calcium ions. However, some main differences in contraction mechanisms are that: 

#The T-tubular system in cardiac muscles have much greater invaginations on the cell surface.
#The [[Sarcoplasmic reticulum|sarcoplasmic reticulum]] is much less complex in comparison to that in the skeletal muscle<ref>Lowe, J. and Stevens, A. (2005:75) Human Histology, 3rd edition, Maryland: Elsevier Mosby.</ref>.

=== References ===

<references />

Calcium ions

2017-11-17T11:20:10Z

170083115: Cleaned up punctuation in reference (before full stop).

=== Importance of Calcium Ions ===

==== Bone Mineralization  ====

Bone rigidity is partially due to a salt in it's osteoid matrix which consists of [[calcium|calcium]] and phosphate ions. If the ion concentrations are above the threshold value then bone mineralization will occur. In order to maintain the ion concentrations:

#[[Osteocalcin|Osteocalcin]], a [[glycoprotein|glycoprotein]], binds to calcium ions within the osteoid.
#Alkalin phosphatase, an [[enzyme|enzyme]], increases the calcium and phosphate ion concentration.
#Matrix vesicles found in the osteoblasts contain alkalin phosphatase. 

If there is a calcium deficiency in the blood, mineralization does not complete causing a disease called "osteomalacia" . This causes the bone to soften and become more vulnerable to damage leading to rickets or other bone deformaties <ref>Lowe, J. and Stevens, A. (2005:256) Human Histology, 3rd edition, Maryland: Elsevier Mosby.</ref>. 

==== Parathyroid Hormone  ====

Parathyroid glands, located in the region of the neck, release the hormone parathormone which maintains the calcium concentration in the blood. In order to increase the concentration it "mobilizes the calcium stored in mineralized bone"<ref>Lowe, J. and Stevens, A. (2005:279) Human Histology, 3rd edition, Maryland: Elsevier Mosby.</ref> by "stimulating osteoclastic activity"<ref>Lowe, J. and Stevens, A. (2005:261) Human Histology, 3rd edition, Maryland: Elsevier Mosby.</ref>. This works by reducing the loss of calcium ions in the kidney and by increasing the reabsorption of the ion into the small intestine.  

When calcium ions levels are persistently low the constant activity of [[parathyroid glands|parathyroid glands]] cause them to swell. This swelling is called parathyroid hyperlasia. Additionally, an over-secretion of parathormone brings about excessive damage to the bone and a surplus of calcium in the blood.  

==== Muscle Contraction  ====

===== Skeletal Muscle Cells  =====

During muscle contraction high concentrations of calcium are required to displace [[troponin|troponin]] and reveal the active site at which myosin binds to for the power stroke. Calcium is released from the sarcoplasmic reticulum through calcium ion channels when the membrane of the T-tubular system is excited. It binds to [[Troponin_C|Troponin C]] causing it to conform, hence permitting the [[myosin|myosin]] head to latch onto the [[actin|actin]] filament, onsetting muscle contraction. <ref>Lowe, J. and Stevens, A. (2005:75) Human Histology, 3rd edition, Maryland: Elsevier Mosby.</ref> 

===== Cardiac Muscle  =====

Similarly to skeletal muscles, the contraction of cardiac muscles is regulated by the concentration of calcium ions. However, some main differences in contraction mechanisms are that: 

#The T-tubular system in cardiac muscles have much greater invaginations on the cell surface.
#The [[Sarcoplasmic reticulum|sarcoplasmic reticulum]] is much less complex in comparison to that in the skeletal muscle<ref>Lowe, J. and Stevens, A. (2005:75) Human Histology, 3rd edition, Maryland: Elsevier Mosby.</ref>.

=== References ===

<references />