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

Lungs

2015-10-23T14:46:58Z

140060517: /* Breathing */

The lung are the [[Organ|organs]] responsible for carrying out breathing and [[Gaseous exchange|gaseous exchange]] in most air-breathing mammals. They are located either side of the [[Heart|heart]] and are enclosed by the [[Rib cage|rib cage]] which provides protection as well as a minor role in the breathing process. In human lungs, the trachea divides into two bronchi that enter into the base of the lungs. The bronchi continually subdivide into the bronchioles which end in hollow cavities known as the alveoli. Alveoli are surrounded by blood vessels which allows gaseous exchange to occur. Gaseous exchange takes place by diffusion with oxygen moving from a high concentration in the lungs to a low concentration in the blood, and carbon dioxide moving into an area of low concentration from a high concentration in the blood. There are on average 300 million alveoli in the adult respiratory system <ref>Gray's Anatomy 38th ed. 1995 Churchill Livingstone. p1670</ref>. 

Around each alveolus is the interstitium, which is a thin layer of cells and blood vessels which provides support for the alveoli. The blood vessels surrounding the alveoli are what gas exchange occurs through.

=== Breathing ===

Breathing (ventilation) is the process by which air enters and is removed from the lungs. Breathing is mainly carried out by the [[Diaphragm|diaphragm]], a sheet of skeletal muscle at the bottom of the rib cage. Contraction of the diaphragm increases the volume of the lungs, thereby decreasing pressure inside them and allowing air to enter. Upon relaxtion of the diaphragm the lungs are compressed and the pressure inside them increases, causing air to leave.  The air within the lungs can also be forced out in active expiration due to the relaxing of the diaphragm and intercostal muscles and the contracting of the abdominal muscles.

=== References ===

<references />

Cancer

2015-10-23T14:44:55Z

140060517:

[[Image:Age specific incidence.gif|right|age specific incidence of cancer in 30-80 year old individuals]][[Image:Japan.gif|right|fig 3. incidence of cancer between different ethnic backgrounds]][[Image:Agr.gif|right|fig 2. Childhood incidence of cancer]] Cancer is an uncontrolled proliferation of [[Cell|cells]] inside the body. These cells have an abnormal [[Mitosis|mitotic]] cycle causing them to grow uncontrollably leading to tumours and thus a [[Disease|disease]] state. Hanahan and Weinberg's [http://www.ncbi.nlm.nih.gov/pubmed/21376230 Hallmarks of Cancer] is a much cited paper that is useful for defining cancer and understanding the six characteristics that many different cancer shares<ref>Hanahan D, Weinberg RA, 'Hallmarks of Cancer: The Next Generation' Cell 144 p646-674, Cell. Available at http://www.cell.com/cell/abstract/S0092-8674(11)00127-9 Last accessed on 24 October 2014.</ref>.  The study and treatment of cancer is known as oncology.

=== Causal factors ===

There are many different forms of cancer associated with every [[Organ|organ]] in the body from the extremely rare (heart cancer) to the four most common cancers ([[Prostate|prostate]], [[Lungs|lung]], [[Breast Cancer|breast]] (women) and [[Colon|colon]]). The causal factors in cancer vary wildly from [[Gene|genetic]] predisposition to environmental [[Carcinogen|carcinogens]] with the exact make up of these carcinogens being highly disputed, but some are widely accepted as cancer causing. Radiation, environmental toxins, [[UV|UV]], [[Obesity|obesity]], [[Virus|viruses]] and chemical carcinogens such as [[Benzene|benzene]]. Equally cancers can be very age specific such as [[Retinoblastoma|retinoblastoma]], which tends to affect the very young. Testicular cancer which tends to affect the 16-25 year old categories and prostate cancer which is a very common in the 60-80 year old category (fig 1 and 2) <ref>Dynamics of Cancer: Incidence, Inheritance, and Evolution.Frank SA.Princeton (NJ): Princeton University Press; 2007. chapter 2, fig 2.2</ref><ref>Dynamics of Cancer: Incidence, Inheritance, and Evolution.Frank SA.Princeton (NJ): Princeton University Press; 2007. chapter 2, fig 2.4</ref>. Genetically predisposed individuals will often develop cancer more severely and often earlier in life. Whereas people from different ethnic backgrounds can have very different cancer incidence curves. This is due to differential genetics between populations and the lifestyles changes that can be seen between countries (fig 3) <ref>Dynamics of Cancer: Incidence, Inheritance, and Evolution.Frank SA.Princeton (NJ): Princeton University Press; 2007. chapter 2, fig 2.21</ref>. The Japanese populous have higher rates of colon and [[Lung|lung]] cancer compared to England in the ~ 30 – 70 age category but by 80 England has nearly caught the rate up. So as you can see there are many factors and differentials related to cancer and its incidence. Old age cancers can strike in the prime of life and childhood cancers can develop late. It is a worldwide issue of great importance and will continue to be far into the future.

=== Treatment of Cancer ===

The treatment of cancer had developed greatly over the last few years. Firstly there are some screening techniques used to catch cancer before it has time to properly develop. These include [[Mammography|mammography]] to screen for breast cancer as well as smear tests to screen for cervical cancer <ref>Roger J. King, Mike W. Robins (2006). Cancer Biology. 3rd ed. Essex: Pearson. p230-62.</ref>. In the majority of cancer cases however the patient detects the symptoms and will then relay these to a doctor who can make a [[Diagnosis|diagnosis]] <ref>Roger J. King, Mike W. Robins (2006). Cancer Biology. 3rd ed. Essex: Pearson. p230-62.</ref>. The three main areas of cancer are [[Surgery|surgery]], [[Chemotherapy|chemotherapy]] and [[Radiotheraphy|radiotheraphy]]. Depending on the type and severity of the cancer depend on which of these are used and often a combination of all of them are required <ref>Roger J. King, Mike W. Robins (2006). Cancer Biology. 3rd ed. Essex: Pearson. p230-62.</ref>.

=== References ===

<references />

MRNA

2015-10-23T13:47:26Z

140060517:

Messenger RNA (mRNA) is an important form of [[RNA|RNA]], both in the body and in the lab. Physiologically, it is used as the coding template for [[Proteins|proteins]], i.e. it directly transcribes the sequence of [[Nucleotide|nucleotides]] from the DNA template (in a process known as [[Transcription|transcription]]), forming a second complementary strand which is later processed by [[RRNA|rRNA]] and [[TRNA|tRNA]] to form a new DNA strand.

There are two forms of mRNA that can be found in eukaryotic cells: [[Pre-mRNA|pre-mRNA]] and [[Mature mrna|mature mRNA]].

Pre mRNA is the exact copy of the DNA sequence, containing [[Intron|introns]] and [[Exon|exons]]. This is not helpful in cloning experiments as bacteria and other [[Prokaryotes|prokaryotes]] do not have the capibility to process this form of mRNA and remove the introns.

Mature mRNA is the product when pre mRNA undergoes ''processing''. This involves a process called 'splicing' which removes the non-coding introns. Processing also encompasses joining the coding exons together, an addition of a CAP at the 5' end and adding a [[Poly A tail|poly A tail to]] the[[3' end| 3' end]], to form a new strand with an uninterrupted sequence, which is then translated into [[Amino_acids|amino acids]] and [[protien|proteins]]. Mature mRNA is required for protein cloning in the lab as it does not require any further processing by the [[Prokaryotes|prokaryotes]].

In the cell, mRNA has a half-life which dictates how long until it degrades naturally, or by enzymatic interactions. The stability of the mRNA can be effected by a number of factors including: length of the poly-A tail, or other proteins bound to it which prevent the action of degrading enzymes.

mRNA can also be used to make [[CDNA|cDNA]] (copy DNA). An enzyme called [[Reverse transcriptase|Reverse transcriptase]] is used to convert mRNA into [[CDNA|cDNA]]. mRNA uses the nucleotide [[Uracil|uracil]], instead of [[Thymine|thymine]], which is found in [[DNA|DNA]].

Protein

2015-10-23T13:42:40Z

140060517: /* Quaternary Structure */

----
A protein is a biological polymer which is made up of [[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, [[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. One important technique used to analyse proteins is [[SDS polyacrylamide-gel electrophoresis|SDS polyacrylamide-gel electrophoresis]] ([[SDS polyacrylamide-gel electrophoresis|SDS-PAGE]]).

== 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 it's structure, therefore each layer is dependant 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 basic sequence of [[Amino acids|amino acids]] joined togther by peptide bond. There are 20 different [[Amino acids|amino acids]] found in nature. This is determined by the [[DNA|DNA]] sequence that encodes for that particular protein: 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 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>

=== Tertiary Structure ===

[[Tertiary structure|Tertiary structure]] relates to the protein function.  If the [[Tertiary structure|tertiary structure]] is wrong 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 stuctures of protein linked together build up a [[Quaternary structure|quaternary structure]].  Quaternary structure can also refer to proteins with an inorganic prosthetic group attatched, an example being haemoglobin: a tetramer consisting of four myoglobin subunits and an iron-containing 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 make up 50% of each cell and have both structural and functional importance. [[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.

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, cell movement, migration of [[chromosomes]] during [[mitosis]] and the direction of 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 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>.

== See also ==

*[[Amino acid|Amino acid]] 

== References ==

<references />

Bidirectional Replication

2014-11-26T18:27:41Z

140060517:

Bidirectional replication is a method of [[DNA|DNA]] replication found in organism from each of the main kingdoms.Bidirectional replication involves replicating DNA in two directions at the same time resulting in a leading strand (were replication occurs more rapidly) and a lagging strand (with slower replication). The properties of each of these strands is caused by [https://teaching.ncl.ac.uk/bms/wiki/index.php/DNA_polymerase DNA polymerase] and its ability to only replicate in the 5' to 3' direction. In the leading strand, a single DNA polymerase can replicate large portions of the strand (approximately X1000-5000 bases before it falls off the DNA due to its high processivity) before dissociating. However, in the lagging strand, the DNA is replicate in chunks which are called [https://teaching.ncl.ac.uk/bms/wiki/index.php/Okasaki_fragments Okasaki fragments]. Each of these fragments is later fused together by [https://teaching.ncl.ac.uk/bms/wiki/index.php/DNA_ligase DNA ligase] to produce the full, unfragmented strand. 

The [[Chromosome|chromosome also]] has two replication forks which are the regions where [[Nucleotides|nucleotides]] are actively added to growing strands. Prokaryotes have a circular chromosome with a single origin of replication (OriC) and a single termination site. However the linear chromosomes, like those in eukaryotes, have several origins of replication and two [[Replication fork|replication forks]] for each of these, replication therefore occurs much more quickly<ref>J.M Berg, J.L Tymoczko, L Stryer, N.D Clarke. (2002). Chapter 27, Section 4: DNA Replication of Both Strands Proceeds Rapidly from Specific Start Sites. Biochemistry. W.H. Freeman and Company.</ref>. At all replication origins, replication takes place in a bidirectional format which results in the formation of ‘[[Replication bubble|replication bubbles]]’. These bubbles grow in size as replication continues. Eventually, two replication forks (at each end of a bubble) meet, at which point they fuse together producing a larger bubble. Ultimately, all the replication bubbles along the [[Chromosome|chromosome]] merge into one large bubble joint only at the [[Telomere|telomeres]]; these split to give two identical strands of [[DNA|DNA]]. This process continues to produce a many strands of DNA which are then passed on to [[Daughter cells|daughter cells]] <ref>Ruvolo, D. L. (2012). Eighth Edition Genetics Analysis of Genes and Genomes. Burlington: Jones &amp; Bartlett Learning.</ref> 

=== References ===

<references />

Okasaki fragments

2014-11-26T18:21:41Z

140060517:

Okasaki fragments are fragments of DNA formed on the lagging strand during bidirectional semiconservative DNA replication. The strands are later fused together by DNA ligase to form the full, unfragmented DNA strand.<ref>Sakabe K, Okazaki R (December 1966). "A unique property of the replicating region of chromosomal DNA". Biochimica et Biophysica Acta 129 (3): 651–54. doi:10.1016/0005-2787(66)90088-8. PMID 5337977.</ref> Each new origin of replication (where the DNA polymerase joins) requires a separate RNA primer. 

'''References:'''

<references />

Okasaki fragments

2014-11-26T18:20:15Z

140060517:

Okasaki fragments

2014-11-26T18:19:25Z

140060517:

Okasaki fragments

2014-11-26T18:18:58Z

140060517:

Okasaki fragments

2014-11-26T18:16:41Z

140060517: Created page with " Okasaki fragments are fragments of DNA formed on the lagging strand during bidirectional semiconservative DNA replication. The strands are later fused together by DNA ligas..."