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

Michaelis menten equation

2014-10-22T10:36:38Z

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The Michaelis-Menten equation is used to work out the '''rate''' '''of [[Enzyme|enzyme]] reactions''' and is written as follows: 

'''                                                     V = Vmax [S] '''

'''                                                           Km + [S]''' 

'''V''''''max''' is the maximum rate of an [[Enzyme|enzyme]] reaction, occurs when all substrate is saturated. 

'''Km''' is the Michaelis-Menten constant and is the substrate concentration at half Vmax . (Higher the Km value, lower the affinity) 

Vmax and Km can also be shown on a graph, the graph which shows this best is a '''double reciprocal plot '''([[Lineweaver-Burk|Lineweaver-Burk]] plot). You can obtain the results by plotting 1/V against 1/[S] <ref>Molecular Biology of the Cell, Alberts et al., 5th Edition (2007) Garland Science, New York Chapter 3 p162-163</ref>.

=== References ===

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F plasmid

2014-10-22T10:34:17Z

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The F plasmid is an example of a large [[Plasmid|plasmid]] which contains genes that allow the plasmids [[DNA|DNA]] to be transferred between cells. It is found in the bacterium [[E. coli|''E. coli'']]; [[E. coli|''E. coli'']] containing this F factor are known as F+ and those without are known as F-. The F stands for fertility and the F factor is around 100000 bases in length. The F+ cells have a tube like structure called a [[Pilus|pilus]] which allows it to make contact with F- cells. This joining via a pilus in order to transfer DNA between bacteria is known as [[Reproduction by Conjugation|conjugation]]. Therefore the F plasmid is known as a [[Conjugative plasmid|conjugative plasmid]]. Within the [[E. coli|''E. coli'']] cells, the F plasmid has one or two copies making it a low-copy number plasmid. During the cell cycle, it replicates once and segregates to both daughter cells <ref>Information and ideas gained from chapter 9, pgs304-305, HartlL. and RuvoloM., (2011) Genetics: Analysis of Genes and Genomes, 8th Edition, Burlington, Jones &amp;amp;amp;amp; Bartlett Learning.</ref>. 

=== Transmission of the F plasmid. ===

Within the F factor are genes which governs the maintenance and transmission of the F plasmid. As already mentioned, the F plasmid is transferred via [[Reproduction by Conjugation|conjugation]] which occurs due the [[Pilus|pilus]] known as the F pilus. All the proteins that are associated with the F pilus are [[Transcription|transcribed]] and [[Translation|translated]] from genes within the F factor. The F plasmid is not transferred to a F- cell via the F pilus, the F pilus merely pulls the two cells together allowing a [[Conjugative junction|conjugative junction]] to form which contains a pore that allows the DNA to pass from the F+ cell to the F- cell. During transfer, the F plasmid unwinds and the outer strand breaks which will be the one that is transferred to the F- cell via the pore in the [[Conjugative junction|conjugative junction]]. Replication of the plasmid then takes place in order to make both single strands of DNA into double stranded DNA plasmids. In the original F+ cell, the sigle strand merely undergoes [[Rolling circle replication|rolling circle replication]] to once again become double stranded. In the recipeint cell, the linear single stranded DNA is replicated into a double strand and becomes a circular F plasmid containing the F factor <ref>Information and Ideas gained from chapter 9, pgs304-305, HartlL. and RuvoloM. (2011) Genetics: Analysis of Genes and Genomes, 8th edition, Burlington, Jones &amp;amp;amp;amp;amp; Bartlett Learning.</ref>. 

Both ''[[E. coli|E. coli]]'' cells are now considered to be F+ cells and therefore can both now transfer the F plasmid and therefore the F factor. This transfer only requires a few minutes although is not effiecent in natural conditions meaning only 10% of naturally occurring ''E. coli'' cells contain the F plasmid and hence the F factor <ref>Information and ideas gained from Chapter 9, pgs 304-305, HartlL. and RuvoloM.(2011)Genetics: Analysis of Genes and Genomes, 8th edition, Burlington, Jones &amp;amp;amp;amp;amp; Bartlett Learning.</ref>. 

NB: F plasmids are unusally large and can accept large scale inserts (up to 300kB) 

=== References: ===

<references />

Plasmid

2014-10-22T10:32:54Z

130066442:

Plasmids are [[Supercoiled|supercoiled]] [[DNA|DNA]] molecules present in most species of [[Bacteria|bacteria]]. These are not integrated into the host [[Chromosome|chromosome]] and are much smaller in length.

Plasmids are not necessary for the survival of a [[Bacteria|bacteria]] but can contain [[Gene|genes]] that are advantageous in changing environmental conditions, an example would be [[Antibiotic resistance|antibiotic resistance]] [[Gene|genes]] <ref>Maloy (1987), Microbial Genetics, 2nd edition, Jones and Bartlett Publishers.</ref>.

Plasmids have no replication machinery of their own and are reliant upon the host for duplication.

Plasmids are very useful as vectors and in [[Recombinant DNA Technology|recombinant DNA techniques]]. Desired [[Genes|genes]] can be inserted in and amplified up.

Examples of plasmids include the puC18, or the F plasmid. Note that the F plasmids are unusually large. This property allows large scale genetic exchange between bacteria. 

=== References ===

<references />

Glutamic acid

2013-11-27T16:37:59Z

130066442:

Glutamic acid (also known as [[Glutamate|Glutamate]]) is a negatively charged [[amino acid|amino acid]] with an [[acidic side chain|acidic side chain]]. It is a vital component in the excitatory pathways of the nervous system in mammals with it's [[gated ion channel|gated ion channels]] being the most common [[ion channels|ion channels]] found in the [[brain|brain]]. Glutamate ion channels found in the [[hippocampus|hippocampus]] are responsible for most of the depolarizing currents of [[Excitatory_postsynaptic_potential|Excitatory PostSynaptic Potentials]] (EPSPs)<ref>ALBERTS, B. (2008). Molecular biology of the cell. New York [etc.], Garland Science. p691</ref>. 

=== ===

Furthermore, Glutamic acid (Glutamate) is involved in Long Term Potentiation (LTP.) LTP is an example of synaptic plascitity.  Glutamate is firstly released from the pre-synaptic neuron. Glutamate then binds to 2 inotropic receptors AMPA and NMDA (the NMDA at this point is currently blocked by magnesium ions though.) 

The AMPA receptor is a Na+ channel so an EPSP is triggers. The EPSP is converted to an action potential is the threshold value (-55mV) is reached.  The depolarization caused as a result trigges the Mg2+ to be ejected from the NMDA receptor. This causes the NMDA receptor to open. As a result, Ca2+ ions flow through the NMDA receptor. 

The Ca2+ activates secondary messenger pathways, and so post-synaptic cell becomes more sensitive to glutamate. The release of Ca2+ causes enhanced neurotransmitter release (so enhanced glutatmate from the pre-synaptic cell.) For example, the Ca2+ can trigger a phorphorylation cascade, causing the phosphorylation of the glutamate receptor channels (AMPA and NMDA.) 

LTP leads to an increase in the quality (and quantity) of synaptic transmission.

=== References ===

''''''(not mentioned). (2013). The Molecular Basis of Learning and Memory. Available: http://www.learner.org/courses/biology/textbook/neuro/neuro_9.html. Last accessed 27th November, 2013.

Gram negative

2013-11-27T11:42:45Z

130066442:

Bacteria are categorised into two main subgroups 'Gram negative' and '[[Gram positive]]' bacteria (with the exception of [[Mycobacterium Tuberculosis]] which falls into neither of the two groups.) The Gram method of classification is dependent upon cell wall structure. In this article I am going to focus on the 'Gram negative' wall structure.

A Gram negative bacteria has a base lipid bi-layer similar to an [[Eukaryotic|eukaryotic]] plasma membrane, surrounded by the [[Periplasmic space|periplasmic space]]. A thin [[Peptidoglycan|peptidoglycan]] layer, much thinner in comparison to that of the gram positive bacteria then arises seperating the two periplasmic compartments. Peptidoglycan is a polymer made up of two repeating units of [[N-acetylmumaric acid|N-acetylmumaric acid and]] [[N-acetylglucosamine|N-acetylglucosamine which]] form linear chains due to cross linkages formed by the tetrapeptide side chains of the monomers. The outermost external barrier of a gram negative bacteria is a lipid like bi-layer, but this is highly disimilar from that of an eukaryotic plasma membrane. The inner leaflet of this outer membrane is studded with [[Lipoproteins|lipoproteins]] which associate to the [[Cytoskelton|cytoskelton]] and peptidoglycan layer. The outer leaflet is made up of [[LPS lipidpolysaccharide|LPS lipidpolysaccharide]]; composed of [[Lipid A|Lipid A]] a fucntional [[Endotoxin|endotoxin]] when released and an [[O polysacharide tail|O polysacharide tail]].

Due to the lipid characteristics of the outermost membrane of the cell wall the gram negative bacteria are stained pink when [[Gram staining|gram stained]].

Gram-negative refers to a classification of bacteria based upon their cell wall structure. Gram-negative bacteria appear red as a result of Gram testing, whereas Gram-positive stain purple.

The structure of the Gram-negative bacterial cell wall is what distinguishes it from [[Gram positive|Gram-positive]] bacteria. Gram-negative bacteria contain a much thinner layer of [[Peptidoglycan|Peptidoglycan]] in comparison to a Gram-positive bacterial cell wall. The Gram-negative cell wall consists of a unique outer membrane, containing [[Lipopolysaccharides|lipopolysaccharides]], murein [[Lipoproteins|lipoproteins]] and porin channels. There is also a periplasmic space between the peptidoglycan cell wall, and the cell membrane.

Gram-negative bacteria exhibit stronger resistance to Antibiotics such as [[Lysozyme|Lysozyme]] and pennicillin G, as well as greater resistance to dyes and detergents. The lipopolysaccharide consists of a core polysaccharide, Lipid A and O-antigen. This lipolysaccharide layer is important in excluding large hydrophobic susbstances from interacting with the cell. Lipid A attaches to the outer membrane ensuring that the lipopolysaccharide remains attached to the cell . References