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

Neurotransmitters

2018-10-22T17:05:22Z

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A neurotransmitter is a chemical messenger utilised to propagate an [[Action potential|action potential]] (or inhibitory response) from one [[Neurone|neurone]] to another. The messenger binds to a [[Receptor|receptor]] on the [[Postsynaptic terminal|postsynaptic terminal]], resulting in the opening of [[Ligand gated ion channels|ligand gated ion channels]], often [[Sodium ion|Na<sup>+</sup>]]. Common neurotransmitters include [[Acetylcholine|Acetyl Choline]], [[Noradrenaline|Noradrenaline]], [[Glutamate|Glutamate]] and [[Dopamine|Dopamine]].

Certain poisons exert their effects by inhibiting neurotransmitter function, such as [[Sarin|Sarin]]. Sarin works by inhibiting [[Acetyl cholinesterase|acetyl cholinesterase]], the [[Enzyme|enzyme]] responsible for breaking down acetyl choline and returning its constituents to the presynaptic terminal <ref>https://pubchem.ncbi.nlm.nih.gov/compound/sarin</ref>.

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Herd immunity

2018-10-22T17:01:21Z

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The intention of [[Vaccination|vaccination]] is to prevent vaccine-preventable [[Disease|disease]], but there are still some immunocompromised individuals in this world. The vaccinated community helps to protect those who are not vaccinated, a concept known as “herd immunity” or “community immunity.” When a critical portion of a community is immunized against a contagious disease, most members of the community are protected against that disease because there is little opportunity for an outbreak. The principle of herd immunity applies to control of a variety of contagious diseases, including [[Influenza|influenza]], [[Measles|measles]], [[Mumps|mumps]], [[Rotavirus|rotavirus]], and [[Pneumococcal|pneumococcal]] disease. Simply put, when a person is vaccinated, they prevent the disease from being spread to others at risk in the community, including:

#Babies too young to receive vaccines
#Unvaccinated children and adults
#Pregnant women
#The elderly
#Individuals with weakened immune systems, such as those with asthma, chronic illness, or undergoing treatment for cancer
#Individuals who are allergic to vaccine components

When less than 90% of children are immunized in a particular community, these pockets of low vaccination create an environment where infectious diseases can take hold and spread. Herd immunity can be only achieved when it exceeds the herd immunity threshold, which means a higher percentage of people in the certain community must be vaccinated<ref>http://www.immunizeforgood.com</ref><ref>https://www.vaccines.gov/basics/protection/index.html</ref>.

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Community immunity

2018-10-22T16:57:49Z

170372743: irrelevant page, view herd immunity

Community immunity

2018-10-22T16:57:21Z

170372743: irrelevant pager

Community immunity

2018-10-22T16:55:39Z

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GAP (GTPase-activating proteins)

2017-12-03T00:01:08Z

170372743: Created page with "GTPase-activating proteins (GAP) otherwise known as GTPase-accelerating proteins are a family of regulatory proteins which bind to activated G-proteins in order to stimulate GTPa..."

GTPase-activating proteins (GAP) otherwise known as GTPase-accelerating proteins are a family of regulatory proteins which bind to activated G-proteins in order to stimulate GTPase activity <ref>Krauss, G. Biochemistry of signal transduction and regulation.Biochemistry and molecular biology education. 2008;36:5:235</ref>. GAPs also known as [[Regulator of G protein signalling (RGS)|RGS]] proteins are essential in regulating G protein activity, which is important as they control many cellular processes such as transduction of signalling from the [[G-protein Coupled Receptor|G protein-coupled receptor]]<ref>Kimple, A.J. Structural Determinants of G-protein α Subunit Selectivity by Regulator of G-protein Signaling 2 (RGS2). The Journal of Biological Chemistry. 2009;284:19402-19411</ref><span style="font-size: 13.28px;">. GAPs function in these processes is to turn off the activity of G proteins, making it produce an opposite effect to [[Guanine nucleotide exchange factor|guanine nucleotide exchange factors (GEFs)]]<ref>Krendel,M. Nucleotide Exchange Factor GEF-H1 Mediates Cross-Talk between Microtubules and the Actin Cytoskeleton. Nature Cell Biology. 2002;4:294–301.</ref></span>

=== Mechanism ===

GAP proteins are closely linked to the activity of G-protein coupled receptors. The activity of these [[G-protein|G-proteins]] is a result of them binding [[GTP|guanosine triphosphate (GTP)]]. The G-proteins can hydrolyse bound GTP to [[GDP|GDP]] and release it, by breaking a phosphate bond, however not very effectively so it is a slow process. This results in a reduction of activity for G-protein coupled receptors and their corresponding processes as it takes longer for them to return to their initial state. GAP proteins therefore make the bound GTP a better target for nucleophilic attack by water, by altering the charge distribution and lowering the [[Transition state|transition state]] <ref>Kötting, C. et al. Time-Resolved FTIR Studies Provide Activation Free Energy, Activation Enthalpy and Activation Entropy for GTPase Reactions. Chemical Physics. 2004;307:227–232.</ref>, making it a more reactive substrate and thus speeding up hydrolysis. By doing this it allows G-protein coupled receptors to be activated more frequently within the cell<ref>Scheffzek, K. et al. The Ras-RasGAP Complex: Structural Basis for GTPase Activation and Its Loss in Oncogenic Ras Mutants. Science. 1997;277:333–338.</ref>. 

=== Classification<br> ===

==== Monomeric<br> ====

GAPs that act on small GTP-binding proteins of the Ras family, have conserved structures and use similar mechanisms.<br>

==== Heterotrimeric<br> ====

GAPs that act on alpha subunits of [[Heterotrimeric G-proteins|heterotrimeric G proteins]], these GAPs belong to the RGS protein family <ref>Das S, Ghosh R, Maitra U. Eukaryotic translation initiation factor 5 functions as a GTPase-activating protein. Journal of biological chemistry. 2001; 276: 6720-6726.</ref>.<br>

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GTPase

2017-12-02T19:39:13Z

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== Overview ==

GTPases are a group of [[Enzyme|enzymes]] which hydrolyse [[GTP|GTP]] to [[GDP|GDP]] (a [[Phosphate|phosphate]] group is removed). They play an important roll in [[Cell signalling|cell signalling]] pathways for example, GTP/GDP bound [[G-proteins|G proteins have intrinsic ]][[GTPase|GTPase]] activity to slowly reset themselves to their resting state state once it has fullfilled its function <ref>Berg J, Tymoczko J and Stryer L, 2007. Biochemistry, 6th Edition, New York: W.H.Freeman &amp;amp;amp;amp;amp;amp;amp;amp;amp; Co Ltd. (page 387)</ref> (Please note not all G proteins have an active intrinsic GTPase activity and require association with [[GAP (GTPase-activating proteins)|GAP]] in order to hydrolyse GTP. They are also involved in the synthesis of [[Proteins|proteins]] at the [[Ribosomes|ribosome]] <ref>Berg J, Tymoczko J and Stryer L, 2007. Biochemistry, 6th Edition, New York: W.H.Freeman &amp;amp;amp;amp;amp;amp;amp;amp; Co Ltd. (page 881)</ref>. They also have roles in [[Vesicle|vesicle]] movement and [[Cell division|cell division]].<br>

The [[G protein alpha subunit|alpha subunit of]] the heterotrimeric G-protein is a GTPase. <ref>Hardin J., Bertoni G., Kleinsmith L., 2011 Beckers World Of The Cell. 8th Edition, San Fransisco: Pearson Education</ref>

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Epinephrine

2017-12-02T19:33:54Z

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Epinephrine is also known as [[Adrenaline|adrenaline]]. It is a [[Steroid hormone|steroid hormone]] which is released by [[Chromaffin cells|chromaffin cells]] in the [[Adrenal gland|adrenal glands]] as part of the 'fight or flight' response. Epinephrine is an amino acid derivative of [[Tyrosine|tyrosine]] secreted from the [[Adrenal medulla|adrenal medulla]]. The polarity of the epinephrine [[Molecule|molecule]] allows it to bind to a stimulatory [[G-proteins|G protein]] which is coupled to [[Beta-adrenergenic receptor|Beta-adrenergenic receptors]] on the surface of the [[Liver|liver]]<ref>Lodish H, Berk A, Zipursky S, Mastudaira P, Balitmore D, Darnell J, Molecular Cell Biology, Section 20.3, 4th edition, W.H. Freeman, 2000</ref>. Initially, the G protein is inactive with guanosine diphosphate ([[GDP|GDP]]) bound. Once epinephrine binds the GDP molecule is released and guanosine triphosphate ([[GTP|GTP]]) is attached, activating the G protein. The [[G protein alpha subunit|alpha subunit]] of the G protein binds to and activates [[Adenylyl cyclase|adenylyl cyclase]] catalysing the conversion of [[ATP|ATP]] to [[CAMP|cAMP]]. cAMP converts [[Phosphorylase α|phosphorylase α]] into [[Phosphorylase β|phosphorylase β]], activating protein kinase A ([[PKA|PKA]])<ref>Citric cycle, Krantz B, Principles of Biochemistry, “Principles of Metabolic Regulation” Chapter 15, Berkeley, 2008</ref>. PKA goes on to phosphorylate other target proteins making [[Glycogen synthase|glycogen synthase]] less active by [[Phosphorylation|phosphorylation]] using a phosphate from ATP resulting in less [[Glycogen|glycogen]] being synthesised<ref>Diwan J, Glycogen Metabolism, 2007 https://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/glycogen.htm, cited on 12/11/2016</ref>. PKA also adds a phosphate to [[Phosphorylase kinase|phosphorylase kinase]]<ref>Diwan J, Glycogen Metabolism, 2007 https://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/glycogen.htm, cited on 12/11/2016</ref>. This activates [[Glycogen phosphorylase|glycogen phosphorylase]], increasing breakdown of glycogen into [[Glucose|glucose]] releasing lots of energy rapidly. One epinephrine-binding molecule can cause activation of hundreds of phosphorylations through amplification of the cell signalling cascade and can produce a permanent change in [[Enzyme|enzyme]] molecules. <sup></sup>This response can be induced by stress or other stimuli in the environment and causes many physiological effects such as increased heart rate, increased blood sugar levels (due to the conversion of [[Glycogen|glycogen]] to [[Glucose|glucose]] in the [[Liver|liver]]); increased breathing rate, constriction of peripheral blood vessels and dilation of the pupils<ref>Alberts et al. (2008:G2), Molecular Biology of the Cell, 5th edition, New York: Garland Science</ref><ref>The American Society of Health-System Pharmacists (2015). https://www.nlm.nih.gov/medlineplus/druginfo/meds/a603002.html date visited 20/10/2015</ref>.

Epinephrine injections can cause side effects such as :

*difficulty breathing
*pounding, fast, or irregular heartbeat
*nausea
*vomiting
*sweating
*dizziness
*nervousness, anxiety, or restlessness
*weakness
*pale skin
*headache
*uncontrollable shaking of a part of your body<ref>American Society of Health-System Pharmacists (2012). https://www.nlm.nih.gov/medlineplus/druginfo/meds/a603002.html</ref>

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