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

Active transport

2018-12-06T19:14:18Z

180224265: Corrected a referencing mistype; citation had a space between it and the last word.

Active transport is the movement of the [[Molecules|molecules]] against their concentration gradient using [[ATP|Adenosine triphosphate (ATP)]] as a source of energy. The molecules move through transmembrane proteins which act as pumps<ref>Berg J, Tymoczko J, Stryer L. (2007) Biochemistry, Sixth edition, New York: WH Freeman</ref>. There are two types of active transport; primary active transport and secondary active transport. Primary active transport is the movement of two different molecules using the energy released from the hydrolysis of [[ATP|ATP]]. It is usually called [[ATPase|ATPase]]; an example of primary active transport is [[Na+/K+ ATPase pump|Na+/K+ ATPase]], this is responsible for about 30% of the overall [[ATP|ATP]] consumption of the body. As the molecule enters the membrane protein, [[ATP|ATP]] binds and is hydrolysed causing [[Phosphorylation|phosphorylation]] of the [[Protein|protein]]. The [[Phosphorylation|phosphorylation]] produces a conformational change of the protein so the molecule is released on the other side of the membrane<ref>Berg J, Tymoczko J, Stryer L. (2007) Biochemistry, Sixth edition, New York: WH Freeman</ref>. [[Secondary active transport|Secondary active transport]] is the co transportation of one molecule by the other; the potential energy produced by the movement of molecule down its concentration gradient is used to drive the movement of another molecule against its concentration gradient. The two molecules can be transported in the same direction across the membrane such as with Na+ - [[Glucose|glucose]], this is known as a [[Symporter|symporter]]. Molecules can also be transported in different directions across the membrane, as one moves into the cell the other moves out, this occurs in the movement of the Na+ - Ca2+ exchanger and is known as an [[Antiporter|antiporter]] . An example of secondary active transport is [[Na+- Ca2+ exchanger|Na+ - Ca2+ exchanger]]  for intracellular Ca2+ [[Homeostasis|homeostasis]]<ref>Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K. and Walter, P. (2008) Molecular biology of the cell, 5th edition, Garland science.</ref>.

Active transport is an excellent example of a process whereas cells require energy, or ATP in this case. Active transport is very important as it allows the cell to uptake essential molecules such as [[Glucose|glucose]] even when they are at low concentrations outside the cell. 

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Vena cava

2018-12-06T19:13:25Z

180224265: Produced a page on the vena cava; discussing function and structure. Provided referencing and links to other pages.

The vena cava is spilt into two structures the superior and the inferior vena cava, forming part of the [[Cardiovascular_system|cardiovascular system]], being the two largest veins in the human body<ref>ThoughtCo. Regina Bailey. Superior and Inferior Venae Cavae. 2018 [Cited 06/12/18]fckLRAvailable from:fckLRhttps://www.thoughtco.com/venae-cavae-anatomy-373253</ref>. The veins are a key component in the pulmonary circulatory system passing [[Deoxygenated_blood|deoxygenated blood]] into the right [[Atrium|atrium]] of the heart from the rest of the body tissues, this allows the blood to then be passed via the hearts double circulatory system into the lungs to be re-oxygenated finally then being pumped through the aorta to the body tissues again allowing continual supply of oxygen to the muscles and cells to meet demand.

 

The superior vena cava, also known as the anterior vena cava, passes deoxygenated blood to the right atrium from the upper cheat regions; head, neck and upper limbs. Positioned beside the aorta and pulmonary artery in the heart structure<ref>ThoughtCo. Regina Bailey. Superior and Inferior Venae Cavae. 2018 [Cited 06/12/18]fckLRAvailable from:fckLRhttps://www.thoughtco.com/venae-cavae-anatomy-373253</ref>. It is formed from the connected brachiocephalic veins, which are positioned either side of the neck, and the azygos vein, which transports deoxygenated blood from the rib cage as it runs up the side of the thoracic vertebral column<ref>healthline. Brachiocephalic vein. 2015 [Cited 06/12/18]fckLRAvailable from:fckLRhttps://www.healthline.com/human-body-maps/brachiocephalic-vein#1</ref>. The azygos vein is connected to both the superior and the inferior vena cava, and this allows an alternate route if there is a blockage in one the veins<ref>healthline. Brachiocephalic vein. 2015 [Cited 06/12/18]fckLRAvailable from:fckLRhttps://www.healthline.com/human-body-maps/brachiocephalic-vein#1</ref>, allowing continuation in the flow of the circulatory system but at a lower efficiency.

 

The inferior vena cava, also referred to as the posterior vena cava, transports deoxygenated blood from the lower and middle regions of the body to the posterior region of the right atrium in the heart. The vein is positioned alongside the spine and travels in parallel to the decending aortic vessel<ref>ThoughtCo. Regina Bailey. Superior and Inferior Venae Cavae. 2018 [Cited 06/12/18]fckLRAvailable from:fckLRhttps://www.thoughtco.com/venae-cavae-anatomy-373253</ref>. It is formed from the connection of the two common iliac veins; the internal iliac vein connects the blood supply from the visceral organs, and the external iliac vein transports the deoxygenated blood from the femoral veins in the legs<ref>healthlineRED. Common iliac vein. 2015 [Cited 06/12/18]fckLRAvailable from:fckLRhttps://www.healthline.com/human-body-maps/common-iliac-vein#1</ref>.

 

Structure: The vena cava have walls comprised of three tissue layers which is characteristic to both arteries and veins; tunica initima, tunica media and tunica externa. The tunica initima is the thinnest and innermost layer, forming the endothelium lining – endothelial cells – which secretes molecules that leads to the promotion of smooth blood flow. Tunica media is the smooth muscle layer also composed of elastic fibres, but at a lower concentration than in the arteries, and connective tissues, all structured in a circular manner around the vessel<ref>lumencandela. Cardiovascular System: Blood Vessels. Blood Vessel Structure and Function. [Cited 06/12/18]fckLRAvailable from:fckLRhttps://courses.lumenlearning.com/boundless-ap/chapter/blood-vessel-structure-and-function/</ref>, this layer forms a connection between the blood vessel and the nervous system<ref>ThoughtCo. Regina Bailey. Superior and Inferior Venae Cavae. 2018 [Cited 06/12/18]fckLRAvailable from:fckLRhttps://www.thoughtco.com/venae-cavae-anatomy-373253</ref>. The outer layer tunica externa is formed primarily of [[Collagen|collagen]]<ref>ThoughtCo. Regina Bailey. Superior and Inferior Venae Cavae. 2018 [Cited 06/12/18]fckLRAvailable from:fckLRhttps://www.thoughtco.com/venae-cavae-anatomy-373253</ref> and connective fibres with an elastic lamina on the outside of the vessel, which is thicker in veins in comparison to arteries, this plays a key function in attaching the vein to the surrounding tissues; anchoring the vein in place is vital to ensure protection, especially to the superficial veins, and to prevent the structures collapsing<ref>lumencandela. Cardiovascular System: Blood Vessels. Blood Vessel Structure and Function. [Cited 06/12/18]fckLRAvailable from:fckLRhttps://courses.lumenlearning.com/boundless-ap/chapter/blood-vessel-structure-and-function/</ref>. 

 

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Nitrogen

2018-12-06T12:10:23Z

180224265: Added in the electron configuration of Nitrogen

An [[Element|element]] represented in the periodic table by the symbol N, of [[Atomic number|atomic number]] 7 and [[Atomic mass|atomic mass]] 14.00674. Has the electron configuration 1s22s22p3. It is a major component of [[Proteins|proteins]]. 

[[DNA]] bases (G,C,A,T) have a nitrogen-carbon ring structure, which are known as nitrogenous bases<ref>Hames, D et al. (2005) Biochemistry, 3rd ed.UK Taylor and Francis p173</ref>. 

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Methylation

2018-12-06T12:05:56Z

180224265: Adjusted the citation format; removing the space

Methylation is a form of [[Alkylation|alkylation]], i.e. the transfer of an [[Alkyl group|alkyl group]] to another [[Molecule|molecule]] . Methylation is specifically the addition or substition of a [[Methyl|methyl group]] to a molecule. [[Methyl groups|Methyl groups]] are alkyls made from [[Methane|methane]] and are [[Carbon|carbon]] [[Atoms|atoms]] attached to 3 [[Hydrogen|hydrogen]] atoms -CH3<ref>March's Advanced Organic Chemistry. Michael B. Smith, Jerry March - John Wiley &amp;amp;amp;amp;amp; Sons (2007)</ref>. It can be involved in the [[Gene expression|expression of genes]], as well as [[Protein|protein]] function regulation and the metabolism of [[RNA|RNA]]. An example of this is the tri-methylation of lysine 36 on the H3 protein (of a histone), which is involved in the response of plants to necrotrophic fungal attack<ref>http://www.plantphysiol.org/content/154/3/1403</ref>. 

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Archaea

2018-12-06T12:04:27Z

180224265: Adjusted the citation format

One of the three major classes major classes of living organisms; previously known as archaebacteria. They are unicellular mircoorganisms that are commonly found living in extreme abiotic conditions such as deep sea vents and extremely salty (hypersaline) [[Water|waters]]. However, some species of archaea are also found living inside your gut, where they were first discovered in 1982<ref>Purdy M. (2006). Gut microbes' partnership helps body extract energy from food, store it as fat. Available: http://news.wustl.edu/news/Pages/7328.aspx. Last accessed 1st Dec 2011</ref>.

The archaea was not recognised as a seperate domain of life until right up to the late 1970s when Dr. Carl Woese and his colleagues at the University of Illinois were studying relationships among the [[Prokaryotes|prokaryotes]] using [[DNA|DNA]] sequences<ref>Speer B.R., Waggoner B. (2001). Introduction to the Archaea Life's extremists. . . Available: http://www.ucmp.berkeley.edu/archaea/archaea.html. Last accessed 1st Dec 2011</ref>. When archaea were first founded they were often grouped as prokaryotes alongside [[Bacteria|bacteria]] under the organism classification system as they do not contain any membrane bound nuclei. Many archaea and bacteria are quite similar in size and shape, although a few archaea have very unusual shapes, for example the ''[[Haloquadratum|Haloquadratum]]'' ("salt square"), a genus of the family ''[[Halobacteriaceae|Halobacteriaceae]]'', which has a very unique structure that looks like flattened square boxes. Nevertheless despite the visual similarity to [[Bacteria|bacteria]], archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably the enzymes involved in [[Transcription|transcription]] and [[Translation|translation]].

The Archaea are very diverse in their metabolism and this allows them to thrive in a wide range of habitats. Halophiles live in habitats with a very high salt content- at least 1.5 moldm-3 and often much higher. These concentrations are usually found in saline lakes such as the Dead Sea<ref>Antonio Ventosa, Joaquín J. Nieto, and Aharon Oren. "Biology of Moderately Halophilic Aerobic Bacteria." Microbiology and Molecular Biology Reviews. N.p., 1998. Web. &amp;lt;http://mmbr.asm.org/content/62/2/504.full&amp;gt;.</ref>. Thermophiles live in very hot habitats, the temperature of which sometimes reach 100°C. For example, hot springs in volcanic areas and geothermally heated regions of the sea floor, including hydrothermal vents known as black smokers<ref>Heather Beal. "Microbial Life in Extremely Hot Environments." Microbial Life in Extremely Hot Environments. Montana State University, n.d. Web. &amp;lt;http://serc.carleton.edu/microbelife/extreme/extremeheat/index.html&amp;gt;.</ref>. Methanogens are spread out in anaerobic habitats where organic matter is available. Examples of these habitats are waterlogged soils, in the gut of cattle and in dumps of organic waste created by humans<ref>Mark Pimentel MD, and Robert P Gunsalus PhD. "Methanogens in Human Health and Disease." Nature.com. Nature Publishing Group, 2012. Web. &amp;lt;http://www.nature.com/ajgsup/journal/v1/n1/full/ajgsup20126a.html&amp;gt;.</ref>.

The archaea are very different to the bacteria and [[Eukaryote|eukaryota]] in they neither require sunlight for [[Photosynthesis|photosynthesis]] as do plants, nor [[Oxygen|oxygen]]. Archaea absorbs [[Carbon dioxide|CO2]], [[Nitrogen|N2]], or [[H2S|H2S]] and give off [[Methane|methane]] gas as a waste product the same way humans breathe in oxygen and breathe out carbon dioxide<ref>Gardiner L.. (2004). Archaea. Available: http://www.windows2universe.org/earth/Life/archaea.html. Last accessed 1st Dec 2011.</ref>.

Recently in 2011, researchers from Washington University and elsewhere have reported that they have sequenced the pan [[Genome|genome]] of the [[Hydrogen|hydrogen]]-consuming gut archaea ''[[Methanobrevibacter smithii|Methanobrevibacter smithii]]''. ''M. smithii'' is an archaeal species that consumes hydrogen in the human gut. Since hydrogen produced during [[Fermentation|fermentation]] of food by bacteria in the gut affects the activity of some bacterial [[Enzyme|enzymes]], this hydrogen use contributes to the energy produced from food<ref>Unknown. (2011). Researchers Sequence Pan Genome of Gut Archaeal Species. Available: http://www.genomeweb.com/sequencing/researchers-sequence-pan-genome-gut-archaeal-species. Last accessed 1st Dec 2011.</ref>.

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Evolution

2018-12-06T11:59:52Z

180224265: Adjusted the citation format; removing the space

''"Nothing in biology makes sense except in the light of evolution."'' - [http://en.wikipedia.org/wiki/Nothing_in_Biology_Makes_Sense_Except_in_the_Light_of_Evolution Theodosius Dobzhansky]. 

The word evolution has has been defined as "the gradual developing of something"<ref>http://oxforddictionaries.com/definition/evolution</ref>.

Some argue that evolution is strictly the change over time, in [[Genes|genes]] and [[Proteins|proteins]], that occur in a population which allow an organism to be advantageous in it's surrounding environment. Organisms change continuously over time due to random mutations; however, the aforementioned definition incorporates that these changes - the evolution of a certain organism, must be beneficial in terms of it's environment. 

Evolutionary changes in metabolism, development and behaviour created three domains<ref>Hartl, D.L. and Ruvolo, M. (2011) 'Genetics: Analysis of Genes and Genomes.' 8th edn. Burlington: Jones and Bartlett Learning.</ref><ref>University of California Museum of Paleontology. (). Mechanisms of Change. Available: http://www.evolution.berkeley.edu.</ref><ref>Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter. (2008) Molecular Biology of the Cell, 5th edition, New York: Garland Science</ref>:

*[[Bacteria|Bacteria]]
*[[Archaea|Archaea]] 
*[[Eukarya|Eukarya]] 

Causes of evolution are mutation, migration, genetic drift and natural selection. 

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Coulomb

2018-12-06T11:59:22Z

180224265: Adjusted the citation format; placing the citation to before the full stop

The coulomb is an SI unit, the unit symbol is a capital C. The coulomb is named in honour of French physicist [[Charles-Augustin de Coulomb|Charles-Augustin de Coulomb]]<ref>Magnet.fsu.edu, (2014). MagLab - Pioneers in Electricity and Magnetism: Charles-Augustin de Coulomb. [online] Available at: http://www.magnet.fsu.edu/education/tutorials/pioneers/coulomb.html [Accessed 27 Nov. 2014].</ref>.

It is a current of electricity or charge being transported at 1 [[Ampere|amp]] per seond.

It can also be measured as 1 [[Farad|farad]] * the potential difference of a [[Volt|volt]].

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Down Syndrome

2018-12-06T11:57:26Z

180224265: Adjusted the citation format; removing the space

Down Syndrome is a condition caused by [[Trisomy 21|trisomy 21]] due to [[Non disjunction|nondisjunction]] in [[Meiosis|meiosis]]. As a result, instead of normal 46 [[Chromosome|chromosomes]], an affected person will have 47 chromosomes. [[Nondisjunction]] of the chromosome number 21 normally occurs in the [[Gamete|gamete of]] the ovum of the mother in her forties. Down syndrome also occurs due to an unusual chromosome structure but at a very small percentage. The similar [[Phenotype|phenotypic]] feature of people with Down Syndrome is that they have broad and flat heads and flattened noses. Affected people have a lower intellectual capacity and defective health with a shortened life expectancy which is less than 50 years<ref>Hartl, D.L., Jones, E.W. (2009) Genetics: Analysis of Genes and Genomes, United States of America: Jones and Bartlet</ref>.

However, it is expected that the life expectancy for individuals with Down syndrome will drastically increase in years to come as there is a new treatment being developed to create effectively a chromosome 21 [[Barr Body|Barr body]]. This would be completed by using a zinc finger nuclease to insert an inducible Xist transgene into embryos with trisomy 21. This gene could then be induced to inactivate the extra chromosome and make up for the extra dosage of these genes, thus hopefully eliminating the effects of the condition.

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Maltase

2018-12-06T11:54:31Z

180224265: Placed the references information that was missing

Maltase is a [[Hydrolytic enzyme|hydrolytic enzyme]] which catalyses the breakdown of the [[Disaccharide|disaccharide]] sugar [[Maltose|maltose]]. The maltose is broken down into two alpha-[[Glucose|glucose]] molecules, the monosaccharide units of maltose, through the hydrolysis of the [[1,4 glycosidic bond|1,4-glycosidic bond]]. It plays a key role in the breakdown of [[Carbohydrates|carbohydrates]], and is present in many organism across nature; plants, bacteria, yeast and mammals. In humans maltase forms part of the digestive system and is synthesised by the [[Epithelial cells|epithelial cells]] of the mucous membrane in the lining of the intestinal wall<ref>Encyclopaedia Britannica. Maltase. 2014 [cited 06/12/18] Available from:fckLRhttps://www.britannica.com/science/maltase</ref>. 

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Maltase

2018-12-06T11:53:10Z

180224265: Added additional information about maltase and the digestive system in humans it is linked with.

Maltase is a [[Hydrolytic enzyme|hydrolytic enzyme]] which catalyses the breakdown of the [[Disaccharide|disaccharide]] sugar [[Maltose|maltose]]. The maltose is broken down into two alpha-[[Glucose|glucose]] molecules, the monosaccharide units of maltose, through the hydrolysis of the [[1,4_glycosidic_bond|1,4-glycosidic bond]]. It plays a key role in the breakdown of [[Carbohydrates|carbohydrates]], and is present in many organism across nature; plants, bacteria, yeast and mammals. In humans maltase forms part of the digestive system and is synthesised by the [[Epithelial_cells|epithelial cells]] of the mucous membrane in the lining of the intestinal wall<ref>Encyclopaedia Britannica. Maltase. 2014 [cited 06/12/18] Available from:
https://www.britannica.com/science/maltase</ref>.

Anaphase

2018-12-03T21:05:16Z

180224265: Corrected a referencing mistype; citation had a space between it and the last word.

Anaphase is the stage of [[Mitosis|mitosis]] and [[Meiosis|meiosis]] where genetic information is moved to opposite poles of the dividing [[Cell|cell]]. In mitosis, with [[Spindles|spindles]] joined to [[Centromeres|centromeres]] and the sister [[Chromatids|chromatids]] lined up on the [[Metaphase plate|metaphase plate]], one chromatid from each pair is pulled to either side of the cell. There are two stages of anaphase in [[Mitosis|mitosis]]. Anaphase A, where [[Chromosome|chromosomes]] move to the poles, is followed by anaphase B, where the poles move apart. [[Anaphase]] occurs twice in meiosis (Anaphase 1 and 2). Anaphase 1 involves the separation of the chromosomes in each bivalent to opposite sides of the cell. Similarly to anaphase in mitosis, anaphase 2 involves the actual splitting of sister chromatids to single chromatids<ref>Mol Biol Cell. 2015 Apr 15; 26(8): 1452–1462. doi: 10.1091/mbc.E14-12-1631</ref>.

[[Image:Anaphase.png]]

''This diagram demonstrates the chromarids being pulled to the poles of the cell by the spindle fibres.([http://www.memrise.com/mem/1260542/pull-away-to-the-poles/ www.memrise.com/mem/1260542/pull-away-to-the-poles/])''

The mitotic spindle elongates during anaphase, this is shown clearly using drosophila embryos. There is a sliding filament mechanism that shows pole motility dictated by a kinesin-5, which has been observed in these embryos.  

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Model organism

2018-12-03T21:04:13Z

180224265: Corrected a referencing mistype; citation was after the full stop.

A model [[Organism|organism]] is one which is studied to further our understanding of biological processes. Typical characteristics of model organisms include developing to maturity rapidly, the ability to be easily manipulated, having a short life span, producing a large number of offspring and to having a sequenced [[Genome|genome]], in addition to being well understood. Model organisms, if possible, need to have cheap sources and be easy to store in a laboratory as well as being non-[[Pathogen|pathogenic]]<ref>Ankeny, R. A. and Leonelli, S., n.d. What’s So Special About Model Organisms?. [Online] Available at: https://ore.exeter.ac.uk/repository/bitstream/handle/10036/3660/Studies_MO_paper_FINAL.pdf?sequence=6 [Accessed 27th December 2014].</ref>. Physiological and biochemical similarities to human cells are also useful in model organisms. Evo Devo is a call for a better choice of model organism due to its phylogenetic position of prospective model organisms, which reflects their evolutionary relationships<ref>University of Bath. "Biologists Call For Better Choice Of Model Organisms In 'Evo-devo'." ScienceDaily. ScienceDaily, 30 March 2007. &amp;lt;www.sciencedaily.com/releases/2007/03/070329092010.htm&amp;gt;.</ref>.

There are different types of model organisms including: Genetic, Genomic and Experimental.

#Genetic model organisms are species amenable to genetic analysis and allow large-scale genetic crosses.
#Genomic model organisms occupy a special position in evolution or have a particular genomic size or composition which can be used for reference e.g the pufferfish.
#Experimental model organisms may not be genetically amenable but have certain other positives, specific to the experiment and what characteristics are being looked for.

Some widely used model organisms are:

*''[[E. coli|E. coli]]''
*''[[S. cerervisiae|S. cerervisiae]]''
*''[[S. pombe|''S. pombe'']]''
*''[[Drosophila melanogaster|Drosophila melanogaster]]''
*''[[C. elegans|C. elegans]]''
*''[[Zebrafish|Zebrafish]]''
*''[[M. Musculus|M. musculus]]'' (mice)
*Amphibians and Birds

=== ''Escherichia coli'' ===

''[[Escherichia coli|Escherichia. coli]]'' are the organism that humans understand the most about. They are a relatively simple rod-shaped [[Bacteria|bacterium]] but have numerous advantages associated with their use as a model organism. They are an organism that has had its [[Genome|genome]] fully sequenced and scientists know more about ''[[E. coli|E. coli]]'' than any other organism. ''E. coli'' are very easy to manipulate and can be grown in a simple [[Nutrient broth|nutrient broth]] in a laboratory, thus, are cheap and easy to keep. ''E. coli'' also have the advantage of reproducing at a very rapid rate as well as developing [[Mutation|mutations]] at a rapid rate<ref>Alberts, B. et al., 2008. Molecular Biology of the Cell. 5th ed. New York: Garland Science.Page 25</ref>.

''E. coli'' have been used for scientists in order to understand many processes that happen in other organisms, such as humans. They have been fundamental in understanding many important mechanisms that occur in all life. An example of this would be that they have enabled us to understand how cells can [[DNA replication|replicate DNA]]<ref>Alberts, B. et al., 2008. Molecular Biology of the Cell. 5th ed. New York: Garland Science. Page 25</ref>.

There are limitations with using ''E. coli'' as a model organism as, most notably, they are a [[Prokaryotic|prokaryotic]] organism and humans are [[Eukaryotic|eukaryotes]]. This ultimately means that there are many differences between the organisms. Eukaryotes are often larger and more complex than prokaryotic organisms, as well as having a larger and more complex [[Genome|genome]]. There is therefore only so much we can learn from prokaryotes, such as E. coli, due to human cells having major differences in terms of the structure and functions of the cell<ref>Alberts, B. et al., 2008. Molecular Biology of the Cell. 5th ed. New York: Garland Science. Page 26</ref>.

=== Yeast ===

[[Yeast|Yeast]] is a unicellular eukaryotic organism and is used as a model organism to try and understand the more complex eukaryotic genome and cell processes. There are many strains that can be used, for example,''[[Saccharomyces cerevisiae|Saccharomyces cerevisiae]]'' and''[[Schizosaccharomyces pombe|Schizosaccharomyces pombe]]'' – ''S. cerevisiae'' is the strain most commonly used. ''S.cerevisaie'' is cheap and easy to use in a laboratory as it just requires a simple nutrient broth to grow, like E. coli. It's [[Genome|genome]] has been fully sequenced and it [[Cell division|divides]] rapidly, although not as rapidly as certain prokaryotes such as ''[[E. coli|E. coli]]''. A further advantage that makes yeast, such as ''S. cerevisiae'', useful as a model organism is that it has a small genome in comparison with higher eukaryotes, but can still carry out all of the most complex processes needed for it to function and survive - this makes it very useful in genetic studies as it is easier to try and find out what is happening in the processes. Using Yeast, such as ''S. cerevisiae'', has been very useful in understanding complex processes such as the [[Eukaryotic cell cycle|eukaryotic cell cycle]]<ref>Alberts, B. et al., 2008. Molecular Biology of the Cell. 5th ed. New York: Garland Science. Pages 33-34</ref>.

=== ''Drosophila melanogaster'' ===

''[[Drosophila melanogaster|Drosophila melanogaster]]'' is a fruitfly and has been used as a model organism, in terms of genetics, for longer than any other organism. Studies on the organism have helped in proving key features of genetics, such as the fact that [[Chromosome|chromosomes]] carry the hereditary genetic information. They are a [[Multicellular|multicellular]] organism, just like humans, and therefore may be more useful in certain studies than yeast<ref>Alberts, B. et al., 2008. Molecular Biology of the Cell. 5th ed. New York: Garland Science. Pages 37-38</ref>.

There are several features that make the ''Drosophila melanogaster'' a useful model organism for genetic studies. It has a giant chromosome that is visible in some of its cells. ''Drosophila'' has a very fast maturation rate and a short lifespan. They have had their [[Genome|genome]] fully sequenced, they are cheap to breed and most importantly there are [[Mutant|mutants]] available for any gene – this allows scientists to understand how [[Mutation|mutations]] in certain genes may cause [[Genetic disorders|genetic defects]]. ''Drosophila'' has played an important role in understanding [[Vertebrates|vertebrate development]]<ref>Alberts, B. et al., 2008. Molecular Biology of the Cell. 5th ed. New York: Garland Science. Pages 37-38</ref>.

=== ''Caenorhabditis elegans'' ===

''[[C. elegans|Caenorhabditis. elegans]]'' are a small worm belonging to the [[Nematode|nematode]] family. They were the first [[Multicellular|multi-cellular]] organism to have their [[Genome|genome]] fully sequenced. They are small, transparent organisms that have 959 cells, all in a particular location. By mapping and studying all of these cells in great detail, it has provided scientists with useful information about the development and these organisms can be useful in trying to understand [[Ageing|ageing]] and [[Cancer|cancer]]. They also can survive indefinitely when placed in a freezer, have had their genome fully sequenced and have a short lifespan – all of these factors make them a very cheap and useful model organism<ref>Alberts, B. et al., 2008. Molecular Biology of the Cell. 5th ed. New York: Garland Science. Pages 36-37</ref>.

=== Zebrafish ===

[[Zebrafish|Zebrafish]], or ''[[Danio rerio|Danio rerio]]'', are a model organism as they have a number of key traits that make them useful to study:

#Transparent [[Embryo|embryos]] that allow us to easily track stages of development. These embryos can also be injected with morpholinos in order to manipulate their development.
#Can be easily genetically manipulated
#Small and therefore cheap and easy to keep.
#Produce a large number of offspring – they can lay up to 200 eggs per week.
#Fully sequenced [[Genome|genome]] and by a great deal of analysis and the creation of [[Genetic maps|genetic maps]], There is a lot of similarity between zebrafish and human genomes.

Genes in humans that cause developmental [[Disease|diseases]] have a counterpart in the zebrafish genome – this, coupled with the ability to [[Gene knockout|knockout]] or cause [[Mutations|mutations]] in certain genes with relative ease presents researchers the opportunity to try and understand these diseases in greater detail<ref>Twyman, R., 2002. Model Organisms: Fish. [Online] Available at: http://genome.wellcome.ac.uk/doc_WTD020806.html [Accessed 28th December 2014].</ref>.

They are widely used in research and one particular trait that they have that is of interest to many scientists is their ability to regenerate damaged parts of their [[Heart|heart]]. Understanding how this happens in great detail may open the door to a better treatment for individuals suffering [[Heart disease|heart disease]]<ref>Jopling, C. et al., 2010. Pubmed. [Online] Available at: http://www.ncbi.nlm.nih.gov/pubmed/20336145 [Accessed 27th December 2014].</ref>.

=== Mice ===

Mice, such as the common house mouse – ''[[Mus. musculus|Mus. musculus]]'', are useful as model organisms as they are [[Mammals|mammals]], just like humans. There are very few differences between mice and humans anatomically or in terms of cell structure etc. This is because all mammals are very similar organisms. They are therefore more similar to humans than any of the examples mentioned above and it is, therefore, more reliable to use them as a model organism when looking to make conclusions about humans. Mice are chosen as the model mammal organism as they are small and therefore easy to keep. They have a fully sequenced genome. Most [[Mutation|mutations]] in a mouse gene correspond to a similar mutation is a human [[Orthologue]], and often a similar phenotype may be expressed. This enables scientists to understand a great deal more about certain genetic diseases that occur in the human population. [[Gene knockdown|Gene knockdowns]] can also provide additional information about the functions of certain [[Genes|genes]] that correspond to certain genes in humans. They are more expensive to keep in a laboratory when compared to some of the model organisms mentioned above but can provide us with a great deal of useful information<ref>Alberts, B. et al., 2008. Molecular Biology of the Cell. 5th ed. New York: Garland Science. Pages 40-41</ref>.

=== Amphibians ===

Amphibians, commonly the frog, are widely used in development research. They have largely replaced Zebrafish in common research. They have a number of features making them particularly useful for research:

#Large embryos that are relatively easy to manipulate
#More similar to Humans than Drosophila and Zebrafish
#Able to regenerate body parts

These model organisms have been used to show how signals from one tissue diffusing to another can direct development.

''Xenopus laevis'' (African clawed frog) is an amphibian model organism that is frequently used when studying the development of the cell cycle and cell signalling. ''Xenopus'' is also used for further research regarding embryonic development and birth defects. There are several features of ''Xenopus laevis ''that make it an appropriate model organism such as it is a tetraploid (has 4 sets of chromosomes), its eggs are very easy to manipulate and the females are able to lay eggs at any time in the year<ref>Tadjuidje, Emmanuel, and Heasman, Janet(Mar 2010) Xenopus as an Experimental Organism. In: eLS. John Wiley and; Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0002030.pub2]</ref><ref>Xenbase: the Xenopus model organism database: Karimi et al. 2017, Nucleic Acids Research, gkx936. [Xenbase / PubMed / NAR ] James-Zorn et al. 2015, Genesis, 53:486-497</ref>.

=== Birds ===

Birds, such as chickens 'Gallus gallus domesticus' or quails 'Coturnix coturnix', have a number of advantages when used as a model organism in developmental biology including:

#Large eggs that are easily accessible
#Easy to manipulate and image development
#Have a very similar anatomy to humans
#Complex genetics
#The use of Birds has been important in the field of physiological studies - their robust embryos have been manipulated with the use of plastic to create the effect of a shell to allow visualisation of development whilst in the embryo<ref>Animal Research Info, 2015, Chicken, viewed 16 October 2018,http://www.animalresearch.info/en/designing-research/research-animals/chicken/</ref>.

Disadvantages include:

#Long life cycle
#Can produce few eggs
#Can be difficult to cross-breed (therefore problematic when looking into genetics)

=== References ===

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