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

Lipolysis

2014-10-10T03:50:46Z

140001668: Created page with "Lipolysis is the breakdown of lipids."

Lipolysis is the breakdown of [[Lipid|lipids]].

2D gel electrophoresis

2014-10-09T03:19:24Z

140001668:

It is a powerful method of separating [[Protein|protein]] along a tubular gel using [[Isoelectric focusing|iso-electric focusing]] and [[SDS polyacrylamide-gel electrophoresis|sodium dodecyl sulphate polyacrylamide gel]]. The sample undergoes [[Isoelectric focusing|iso-electric focusing]] first; an electrical current is passed through a gel with a [[pH gradient|pH gradient]], and the proteins stop moving when they reach the pH at which they have no net charge - this is known as the [[Isoelectric point|Iso-electric point]] (pI). The sample is then placed horizontally on top of [[SDS-PAGE|SDS-PAGE]] and spreads across. The sample then moves vertically down again to yield the second dimension based on the size of the protein, producing a 2D pattern. So the sample has been separated by virtue of [[Isoelectric point|Iso-electric point]] (pI), when they move horizontally and by virtue of their size; when they move down vertically. 

Because of the specificity of this method, it is possible to identify over one thousand proteins on the same gel, in one experiment <ref>Stryer, Lubert; Tymoczko, John L.; Berg, Jeremy M., (2012) Biochemistry, 7th Edition, New York: WH Freeman and Co. Page 74</ref>. 

=== References ===

<references />

Gene linkage

2013-11-23T12:11:50Z

140001668:

Gene linkage is a phenomenon that occurs when two or more genes situated at different loci on the same chromosome segregate together during anaphase of [[Meiosis|meiosis]] and become distributed into the same gamete. The loci are usually close to each other. Linked genes segregate together unless [[Recombination|recombination]] occurs. Gene linkage is an exception to [[Mendel's Second Law|Mendel's second law of inheritance]], the law of [[Principle of Independent Assortment|independent assortment]].

The distance between loci can be estimated by calculating the recombination frequency (RF) ,in %, in offspring in a genetic cross and is measured in [[Centimorgan|centimorgan]] (cM) or map unit (m.u.). The greater the distance between loci, the greater the chance of genes being separated into different gametes due to [[Recombination|recombination]] and crossing over. RF cannot be greater than 50%. Linked genes have RF of less than 50% or distance of less than 50cM whereas unlinked genes have RF of 50% and can be more than 50cM apart. 

Sodium-calcium Exchanger

2013-11-17T16:55:19Z

140001668: Created page with "The sodium-calcium exchanger is an antiporter in theplasma membrane of a cell that transports sodium ions into the cell and calcium ions out of..."

The sodium-calcium exchanger is an [[Antiporter|antiporter]] in the[[Plasma_membrane|plasma membrane]] of a cell that transports sodium ions into the cell and calcium ions out of the cell by [[secondary active transport|secondary active transpor]]t. It uses the downward Na+ gradient into the cell created by [[Sodium_potassium_pump|sodium pumps]] using ATP to power the uphill transport of Ca2+ out of the cell. It is effective at high Ca2+ concentrations.

The sodium-calcium exchanger is important in the regulation of calcium ions in a cell. Cytosolic calcium concentration is kept low because calcium ions can act as a trigger for many processes, such as [[muscle contraction|muscle contraction]] and [[Cell_signalling_pathways|cell signalling pathway]].

Polyploidy

2013-11-17T16:19:49Z

140001668: Created page with "Polyploidy is a rare condition in which there are more than two sets of chromosomes in an organism. An organism with polyploidy is known as a polyploid. Polyploids are usually in..."

Polyploidy is a rare condition in which there are more than two sets of chromosomes in an organism. An organism with polyploidy is known as a polyploid. Polyploids are usually infertile. Polyploidy is usually due to nondisjunction during meiosis in parental cells, although it may also occur by abnormalities in mitosis.

Gene linkage

2013-11-15T13:42:54Z

140001668:

Gene linkage is a phenomenon that occurs when two or more genes situated at different loci on the same chromosome segregate together during anaphase of [[Meiosis|meiosis]] and become distributed into the same gamete. The loci are usually close to each other. Linked genes segregate together unless [[Recombination|recombination]] occurs. Gene linkage is an exception to [[Mendel's Second Law|Mendel's second law of inheritance]], the law of [[Principle of Independent Assortment|independent assortment]].

The distance between loci can be estimated by calculating the recombination frequency (RF) ,in %, in offspring in a genetic cross and is measured in centiMorgan(cM) or map unit(m.u.). The greater the distance between loci, the greater the chance of genes being separated into different gametes due to [[Recombination|recombination]] and crossing over. Linked genes have RF of less than 50% whereas unlinked genes have RF of more than 50%.

Recombination

2013-11-15T13:37:04Z

140001668:

Recombination is a process that involves crossing over between chromosomes which subsequently results in exchange of genetic material between the chromosomes. There are three types of genetic recombination and they are homologous recombination, site-specific recombination and somatic recombination. The process normally involves strand invasion followed by strand breakage, which leads to formation of Holliday junction. Resolution of Holliday junction gives rise crossover or noncrossover products. Mismatch repair of heteroduplexes which usually occurs after that may lead to gene conversion. There are several models for genetic recombination, and they include the Double Holliday Junction(DHJ) model and Synthesis-Dependent Strand Annealing(SDSA) model 

 

Homologous recombination, [[Principle of Independent Assortment|independent assortment]] of chromosomes during meiosis and random fertilisation of parental gametes are the main contributors of genetic variation in offspring.

 

Homologous recombination during meiosis may prevent [[Gene_linkage|gene linkage]].

Recombination

2013-11-15T13:29:22Z

140001668:

Recombination is a process that involves crossing over between chromosomes which subsequently results in exchange of genetic material between the chromosomes. There are three types of genetic recombination and they are homologous recombination, site-specific recombination and somatic recombination. The process normally involves strand invasion followed by strand breakage, which leads to formation of Holliday junction. Resolution of Holliday junction gives rise crossover or noncrossover products. Mismatch repair of heteroduplexes which usually occurs after that may lead to gene conversion.  

Homologous recombination, [[Principle_of_Independent_Assortment|independent assortment]] of chromosomes during meiosis and random fertilisation of parental gametes are the main contributors of genetic variation in offspring.

Recombination

2013-11-15T13:26:00Z

140001668: Created page with "Recombination is a process that involves crossing over between chromosomes which subsequently results in exchange of genetic material between the chromosomes. There are three typ..."

Action potential

2013-11-15T13:09:05Z

140001668:

An action potential is a message in the form of an electrical impulse caused by a rapid change in a cell's membrane potential.

When a stimulus reaches the threshold at the [[Axon hillock|axon hillock]], an action potential begins.

An action potential relies on many [[Protein|protein]] channels.  In a neurone, the [[Potassium leak channel|Potassium leak channel]] and [[Sodium pump|Sodium pump]] maintain the resting potential. The [[Sodium voltage-gated ion channels|voltage gated sodium channel]] and the [[Voltage gated potassium channels|voltage gated potassium channel]] are involved in the progression of an action potential along the membrane.

The action potential progression can be separated into a several steps; 

#Voltage channels are closed and the Potassium leak channel and the sodium pump maintain the resting membrane potential of -70 mV by the movement of .
#The [[Neurone|neurone]] becomes stimulated. The [[Voltage gated sodium channels|voltage gated sodium channels]] begin to open and the membrane potential begins to slowly depolarises and sodium enters the cell down its concentration gradient. All the voltage gated Sodium channels open when the membrane potential reaches around -55 mV and there's a large influx of Sodium, causing a sharp rise in voltage. As the potential nears +30mV, the rate of depolarisation slows down as the voltage gated Sodium channels become saturated and inactivate, preventing further sodium ions from entering the cell.
#[[Voltage gated potassium channels|Voltage gated potassium channels]] open, and [[Potassium|potassium]] leaves the cell down its concentration gradient. The depolarisation of the cell stops and repolarisation can occur through these voltage gated Potssium channnels.
#Voltage gated sodium channels are completely deactivated and potassium floods out through the [[Voltage gated potassium channels|voltage gated potassium channels]],
#Voltage gated potassium channels are slow to close, and therefore [[Hyperpolarisation|hyperpolarisation]] occurs. This is where the membrane potential drops below the resting potential of -70 mV as potassium continues to leave.
#Once the [[Voltage gated potassium channels|voltage gated potassium channels]] close, the resting state can be re-established through the Potassium leak channel and Sodium pump. 

The action potential travels along the neurone's [[Axon|axon via]] current loops in order to reach the [[Axon terminal|axon terminal]].

An action potential is a transient, electrical signal, which is caused by a rapid change in [[Resting membrane potential|resting membrane potential ]](-70 mV). This occurs when the [[Threshold potential|threshold potential]] (-55 mV) is reached, this causes a rapid opening in the voltage gated sodium channels leading to a influx of sodium into the cell.  The [[Threshold potential|threshold potential]] also causes a slow opening of voltage gated potassium channels leading to the eflux of potassium out of the cell. This causes the cell to [[Depolarisation|depolarise]], meaning the inside of the cell is now positive compared to the outside.

The action potenial starts in the axon hilock as there is a high density of voltage gated sodium channels here, it is also where [[Graded potentials|graded potentials]] need to reach the threshold potential to cause a action potential. If the do not reach the [[Supratheshold|supratheshold level]], then an Action Potenitial is not triggered and the graded potenital is known as [[Subthreshold|subthreshold]]. Above threshold, increase in the strength of a stimulus will not increase the size of the corresponding action potential. The strength of a stimulus, or the size of a graded potential, is indicated by frequency of action potentials travelling along a neurone.

The action potential travels via current loops. In myelinated axons its jumps from [[Node of ranvier|node of ranvier]] to node of ranvier, this is known as [[Saltatory conduction|saltatory conduction]].

The higher the density of the [[Myelin Sheath|myelin sheaths]] and higher the membrane resistance of the myelinated axon, the faster the axon potential can travel.

The point at which the membrane of an axon is depolarised causes a local circuit to be set up between the depolarised region and the region either side of it. This causes the resting at regions either side to become depolarised also. In this way the action potential sweeps along the axon.

The [[Refractory Period|refractory period prevents]] the action potential from travelling backwards. There are two types of refractory periods, the absolute refractory period and the relative refractory period. The absolute refractory period is when the membrane cannot generate another action potential no matter how large the stimulus is, this is because the voltage- gated sodium ion channels are inactivited. The relative refactory period is when the membrane can produce another action potential if the stimulus is larger than normal, this is because the voltage-gated soduim ion channels have recoveredand the voltage-gated potassium ion channels are still open. The relative refractory period is the period of hyperpolarisation after an action potential <ref>The McGill Physiology Virtual Lab, Refractory Period. Available at: http://www.medicine.mcgill.ca/physio/vlab/cap/refract.htm (Last accessed 9.11.13)</ref>.

=== References ===

<references />

Gene linkage

2013-11-15T12:53:41Z

140001668:

Gene linkage

2013-11-15T12:52:30Z

140001668: Created page with "Gene linkage is a phenomenon that occurs when two or more genes situated at different loci on the same chromosome segregate together during anaphase of meiosis and be..."