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Heart attack

2014-10-16T11:16:13Z

130077415: Created page with "= What is a Heart Attack? = A heart attack, or myocardial infarction is the consequence of poor blood flow to the heart, which means that the muscle does not receive the amount ..."

= What is a Heart Attack? =

A heart attack, or myocardial infarction is the consequence of poor blood flow to the heart, which means that the muscle does not receive the amount of oxygen that it needs. This is commonly due to the blockage of one of the coronary arteries which supplies the heart muscle with blood.

== Symptoms ==

Someone suffering a heart attack can often present with chest pain, but can also suffer from:

*sweating
*anxiety
*shortness of breath
*feeling of weakness
*fatigue

== Prevention ==

Lifestyle choices can have a major contribution to the risk of myocardial infarction. Tobacco smoking, high alcohol consumption and a diet high in saturated fat all appear to increase the risk of heart attacks.

Regular exercise and a balanced healthy diet low in saturated fat may help to reduce the risk of a heart attack.

DNA

2013-11-16T15:19:29Z

130077415:

[[Image:BASE PAIRINGS.png|left|DNA Helix]]

DNA (deoxyribonucleic acid) is the genetic information found in the [[Nucleus|nuclei]] of most [[Organism|organisms]]. It is arranged into structures called [[Chromosome|chromosomes]]. The structure of DNA was first identified as having a 'double-helix' structure by [[Watson|Watson]] and [[Crick|Crick]] in 1953. DNA is composed of 4 [[Base|bases]]: the [[Purine|purines]]: [[Adenine|adenine]] (A) and [[Guanine|guanine]] (G); and the [[Pyrimidine|pyrimidines]]: [[Thymine|thymine]] (T) and [[Cytosine|cytosine]] (C) <ref>HARTL AND JONES,2009:41, GENETICS : ANALYSIS OF GENES AND GENOMES SEVENTH EDITION.</ref>. These form complementary base pairs of AT and GC. DNA also contains a [[Phosphates|phosphate]] group connected to a [[Deoxyribose sugar|deoxyribose sugar]]. The phosphate group is attached to the sugar through a [[Phosphodiester bond]].  

=== Structure of DNA ===

DNA is a chain of monomers (repeating units) called "nucleotides". A [[nucleotide]] consists of: a [[Deoxyribose|2` deoxyribose sugar]] (A five ([[Pentose|pentose]]) [[Carbon|carbon]] sugar  similar to that of [[Ribose|ribose]] sugar found in [[RNA|RNA]]. Its chemical formula is C5H10O4), a [[Phosphate group|phosphate group]] (contains one [[Phosphorus|phosphorus]] [[Atom|atom]], bonded to 4 [[Oxygen|oxygens]] and forms a [[Phosphodiester bond|phosphodiester bond]], which connects 2 [[Deoxyribose|deoxyribose sugars]] together resulting in the formation of a chain) and a nitrogenous base (one from A, C, G or T, which forms a side chain branching from the 2` deoxyribose sugar).

The 2` deoxyribose sugar/phosphate group region is regarded as the 'backbone' of DNA strands due to its structural purpose and the sequence of bases carries the gentic information. In order to produce a double stranded DNA structure, interactions occur between complementary bases. The complementary base pairs in DNA interact with one another via [[Hydrogen bonds|hydrogen bonds]]: A-T interactions consist of 2 intermolecular [[Hydrogen bonds|hydrogen bonds]], whereas G-C interactions consist of 3 intermolecular [[Hydrogen bonds|hydrogen bonds]]. These interactions form bridges between two DNA chains, thus creating a double stranded 'ladder' shaped structure. Each strand acts as a template for the other one in DNA replication. DNA is copied into [[MRNA|mRNA]] (messenger RNA) which carries the information from the original DNA template strand to be involved in protein synthesis.  The process of DNA being copied into mRNA is termed [[Transcription]] . The transcripted mRNA is then translated in a process called [[Translation]] by [[TRNA]].

Despite many other theories, in 1953 [[James watson|James Watson]] and Frances Crick discovered the true structure of a double stranded DNA molecule to be a 'Double Helix'. This was solved as a result of 'stick-and-ball' models they created, along with utilising the work of fellow scientists [[Rosalind Franklin|Rosalind Franklin]] and [[Maurice Wilkins|Maurice Wilkins]] on [[X-ray crystallography|X-ray crystallography]]<ref>http://nobelprize.org/educational/medicine/dna_double_helix/readmore.html</ref> . The [[X-ray diffraction|X-ray diffraction]] photographs obtained from [[DNA|DNA]] fibres, displayed a unique X-shape, which illustrates a helical stucture, although they indicated a repeating structure of 3.4 Å apart per turn of the helix, each base is roated 36 degrees from the next one. The diameter of the helix is 20Â. They found that the sugar-phosphate backbone was on the outside and the bases are positioned on the inside of the helix <ref>http://www.chm.bris.ac.uk/motm/dna/dna.htm</ref><ref>J.Berg, J.Tymoczko, L.Stryer;, 113-115, 2012 Freeman; Biochemistry</ref>. 

The DNA of the Indian muntjac which is an Asiatic deer has the longest length ( approximately 3 billion nucleotides) among all the known DNA molecules of other organisms.<ref name="null">Berg, J.M, Biochemistry, 7th ed, 2012:117</ref>

=== Replication ===

The double stranded nature of DNA is essential to the method of replication, called; "semi-consrvative replication". In this process, the [[enzyme]] DNA helicase unwinds the double helix by breaking the hydrogen bonds between the complementary bases on each strand revealing the 2 seperate strands. On these strands are the revealed bases, which attract complementary bases on free nucleotides. The free nucleotides are joined together by an [[enzyme]] DNA polymerase. The joining of nucleotides forms a new strand of DNA which is identical to the other double strand of DNA, as it uses one of the original strands as a template for replication. Each daughter double strand of DNA is made up of a parent strand and a newly sythesised strand. 

=== References ===

<references />

DNA

2013-11-16T15:17:52Z

130077415:

[[Image:BASE PAIRINGS.png|left|DNA Helix]]

DNA (deoxyribonucleic acid) is the genetic information found in the [[Nucleus|nuclei]] of most [[Organism|organisms]]. It is arranged into structures called [[Chromosome|chromosomes]]. The structure of DNA was first identified as having a 'double-helix' structure by [[Watson|Watson]] and [[Crick|Crick]] in 1953. DNA is composed of 4 [[Base|bases]]: the [[Purine|purines]]: [[Adenine|adenine]] (A) and [[Guanine|guanine]] (G); and the [[Pyrimidine|pyrimidines]]: [[Thymine|thymine]] (T) and [[Cytosine|cytosine]] (C) <ref>HARTL AND JONES,2009:41, GENETICS : ANALYSIS OF GENES AND GENOMES SEVENTH EDITION.</ref>. These form complementary base pairs of AT and GC. DNA also contains a [[Phosphates|phosphate]] group connected to a [[Deoxyribose sugar|deoxyribose sugar]]. The phosphate group is attached to the sugar through a [[Phosphodiester bond]].  

=== Structure of DNA ===

DNA is a chain of monomers (repeating units) called "nucleotides". A [[nucleotide]] consists of: a [[Deoxyribose|2` deoxyribose sugar]] (A five ([[Pentose|pentose]]) [[Carbon|carbon]] sugar  similar to that of [[Ribose|ribose]] sugar found in [[RNA|RNA]]. Its chemical formula is C5H10O4), a [[Phosphate group|phosphate group]] (contains one [[Phosphorus|phosphorus]] [[Atom|atom]], bonded to 4 [[Oxygen|oxygens]] and forms a [[Phosphodiester bond|phosphodiester bond]], which connects 2 [[Deoxyribose|deoxyribose sugars]] together resulting in the formation of a chain) and a nitrogenous base (one from A, C, G or T, which forms a side chain branching from the 2` deoxyribose sugar).

The 2` deoxyribose sugar/phosphate group region is regarded as the 'backbone' of DNA strands due to its structural purpose and the sequence of bases carries the gentic information. In order to produce a double stranded DNA structure, interactions occur between complementary bases. The complementary base pairs in DNA interact with one another via [[Hydrogen bonds|hydrogen bonds]]: A-T interactions consist of 2 intermolecular [[Hydrogen bonds|hydrogen bonds]], whereas G-C interactions consist of 3 intermolecular [[Hydrogen bonds|hydrogen bonds]]. These interactions form bridges between two DNA chains, thus creating a double stranded 'ladder' shaped structure. Each strand acts as a template for the other one in DNA replication. DNA is copied into [[MRNA|mRNA]] (messenger RNA) which carries the information from the original DNA template strand to be involved in protein synthesis.  The process of DNA being copied into mRNA is termed [[Transcription]] . The transcripted mRNA is then translated in a process called [[Translation]] by [[TRNA]].

Despite many other theories, in 1953 [[James watson|James Watson]] and Frances Crick discovered the true structure of a double stranded DNA molecule to be a 'Double Helix'. This was solved as a result of 'stick-and-ball' models they created, along with utilising the work of fellow scientists [[Rosalind Franklin|Rosalind Franklin]] and [[Maurice Wilkins|Maurice Wilkins]] on [[X-ray crystallography|X-ray crystallography]]<ref>http://nobelprize.org/educational/medicine/dna_double_helix/readmore.html</ref> . The [[X-ray diffraction|X-ray diffraction]] photographs obtained from [[DNA|DNA]] fibres, displayed a unique X-shape, which illustrates a helical stucture, although they indicated a repeating structure of 3.4 Å apart per turn of the helix, each base is roated 36 degrees from the next one. The diameter of the helix is 20Â. They found that the sugar-phosphate backbone was on the outside and the bases are positioned on the inside of the helix <ref>http://www.chm.bris.ac.uk/motm/dna/dna.htm</ref><ref>J.Berg, J.Tymoczko, L.Stryer;, 113-115, 2012 Freeman; Biochemistry</ref>. 

The DNA of the Indian muntjac which is an Asiatic deer has the longest length ( approximately 3 billion nucleotides) among all the known DNA molecules of other organisms.<ref name="null">Berg, J.M, Biochemistry, 7th ed, 2012:117</ref>

=== Replication ===

The double stranded nature of DNA is essential to the method of replication, called; "semi-consrvative replication". In this process, the enzyme DNA helicase unwinds the double helix by breaking the hydrogen bonds between the complementary bases on each strand revealing the 2 seperate strands. On these strands are the revealed bases, which attract complementary bases on free nucleotides. The free nucleotides are joined together by an enzyme DNA polymerase. The joining of nucleotides forms a new strand of DNA which is identical to the other double strand of DNA, as it uses one of the original strands as a template for replication. Each daughter double strand of DNA is made up of a parent strand and a newly sythesised strand. 

=== References ===

<references />

DNA

2013-11-16T15:11:59Z

130077415:

[[Image:BASE PAIRINGS.png|left|DNA Helix]]

DNA (deoxyribonucleic acid) is the genetic information found in the [[Nucleus|nuclei]] of most [[Organism|organisms]]. It is arranged into structures called [[Chromosome|chromosomes]]. The structure of DNA was first identified as having a 'double-helix' structure by [[Watson|Watson]] and [[Crick|Crick]] in 1953. DNA is composed of 4 [[Base|bases]]: the [[Purine|purines]]: [[Adenine|adenine]] (A) and [[Guanine|guanine]] (G); and the [[Pyrimidine|pyrimidines]]: [[Thymine|thymine]] (T) and [[Cytosine|cytosine]] (C) <ref>HARTL AND JONES,2009:41, GENETICS : ANALYSIS OF GENES AND GENOMES SEVENTH EDITION.</ref>. These form complementary base pairs of AT and GC. DNA also contains a [[Phosphates|phosphate]] group connected to a [[Deoxyribose sugar|deoxyribose sugar]]. The phosphate group is attached to the sugar through a [[Phosphodiester bond]].  

=== Structure of DNA ===

DNA is a chain of monomers (repeating units) called "nucleotides". A nucleotide consists of: a [[Deoxyribose|2` deoxyribose sugar]] (A five ([[Pentose|pentose]]) [[Carbon|carbon]] sugar  similar to that of [[Ribose|ribose]] sugar found in [[RNA|RNA]]. Its chemical formula is C5H10O4), a [[Phosphate group|phosphate group]] (contains one [[Phosphorus|phosphorus]] [[Atom|atom]], bonded to 4 [[Oxygen|oxygens]] and forms a [[Phosphodiester bond|phosphodiester bond]], which connects 2 [[Deoxyribose|deoxyribose sugars]] together resulting in the formation of a chain) and a nitrogenous base (one from A, C, G or T, which forms a side chain branching from the 2` deoxyribose sugar).

The 2` deoxyribose sugar/phosphate group region is regarded as the 'backbone' of DNA strands due to its structural purpose and the sequence of bases carries the gentic information. In order to produce a double stranded DNA structure, interactions occur between complementary bases. The complementary base pairs in DNA interact with one another via [[Hydrogen bonds|hydrogen bonds]]: A-T interactions consist of 2 intermolecular [[Hydrogen bonds|hydrogen bonds]], whereas G-C interactions consist of 3 intermolecular [[Hydrogen bonds|hydrogen bonds]]. These interactions form bridges between two DNA chains, thus creating a double stranded 'ladder' shaped structure. Each strand acts as a template for the other one in DNA replication. DNA is copied into [[MRNA|mRNA]] (messenger RNA) which carries the information from the original DNA template strand to be involved in protein synthesis.  The process of DNA being copied into mRNA is termed [[Transcription]] . The transcripted mRNA is then translated in a process called [[Translation]] by [[TRNA]].

Despite many other theories, in 1953 [[James watson|James Watson]] and Frances Crick discovered the true structure of a double stranded DNA molecule to be a 'Double Helix'. This was solved as a result of 'stick-and-ball' models they created, along with utilising the work of fellow scientists [[Rosalind Franklin|Rosalind Franklin]] and [[Maurice Wilkins|Maurice Wilkins]] on [[X-ray crystallography|X-ray crystallography]]<ref>http://nobelprize.org/educational/medicine/dna_double_helix/readmore.html</ref> . The [[X-ray diffraction|X-ray diffraction]] photographs obtained from [[DNA|DNA]] fibres, displayed a unique X-shape, which illustrates a helical stucture, although they indicated a repeating structure of 3.4 Å apart per turn of the helix, each base is roated 36 degrees from the next one. The diameter of the helix is 20Â. They found that the sugar-phosphate backbone was on the outside and the bases are positioned on the inside of the helix <ref>http://www.chm.bris.ac.uk/motm/dna/dna.htm</ref><ref>J.Berg, J.Tymoczko, L.Stryer;, 113-115, 2012 Freeman; Biochemistry</ref>. 

The DNA of the Indian muntjac which is an Asiatic deer has the longest length ( approximately 3 billion nucleotides) among all the known DNA molecules of other organisms.<ref name="null">Berg, J.M, Biochemistry, 7th ed, 2012:117</ref>

=== Replication ===

The double stranded nature of DNA is essential to the method of replication, called; "semi-consrvative replication". In this process, the enzyme DNA helicase unwinds the double helix by breaking the hydrogen bonds between the complementary bases on each strand revealing the 2 seperate strands. On these strands are the revealed bases, which attract complementary bases on free nucleotides. The free nucleotides are joined together by an enzyme DNA polymerase. The joining of nucleotides forms a new strand of DNA which is identical to the other double strand of DNA, as it uses one of the original strands as a template for replication. Each daughter double strand of DNA is made up of a parent strand and a newly sythesised strand. 

=== References ===

<references />

DNA

2013-11-16T14:56:17Z

130077415:

[[Image:BASE PAIRINGS.png|left|DNA Helix]]

DNA (deoxyribonucleic acid) is the genetic information found in the [[Nucleus|nuclei]] of most [[Organism|organisms]]. It is arranged into structures called [[Chromosome|chromosomes]]. The structure of DNA was first identified as having a 'double-helix' structure by [[Watson|Watson]] and [[Crick|Crick]] in 1953. DNA is composed of 4 [[Base|bases]]: the [[Purine|purines]]: [[Adenine|adenine]] (A) and [[Guanine|guanine]] (G); and the [[Pyrimidine|pyrimidines]]: [[Thymine|thymine]] (T) and [[Cytosine|cytosine]] (C) <ref>HARTL AND JONES,2009:41, GENETICS : ANALYSIS OF GENES AND GENOMES SEVENTH EDITION.</ref>. These form complementary base pairs of AT and GC. DNA also contains a [[Phosphates|phosphate]] group connected to a [[Deoxyribose sugar|deoxyribose sugar]]. The phosphate group is attached to the sugar through a [[Phosphodiester bond]].  

=== Structure of DNA ===

DNA is a chain of monomers (repeating units) called "nucleotides". A nucleotide consists of: a [[Deoxyribose|2` deoxyribose sugar]] (A five ([[Pentose|pentose]]) [[Carbon|carbon]] sugar  similar to that of [[Ribose|ribose]] sugar found in [[RNA|RNA]]. Its chemical formula is C5H10O4), a [[Phosphate group|phosphate group]] (contains one [[Phosphorus|phosphorus]] [[Atom|atom]], bonded to 4 [[Oxygen|oxygens]] and forms a [[Phosphodiester bond|phosphodiester bond]], which connects 2 [[Deoxyribose|deoxyribose sugars]] together resulting in the formation of a chain) and a nitrogenous base (one from A, C, G or T, which forms a side chain branching from the 2` deoxyribose sugar).

The 2` deoxyribose sugar/phosphate group region is regarded as the 'backbone' of DNA strands due to its structural purpose and the sequence of bases carries the gentic information. In order to produce a double stranded DNA structure, interactions occur between complementary bases. The complementary base pairs in DNA interact with one another via [[Hydrogen bonds|hydrogen bonds]]: A-T interactions consist of 2 intermolecular [[Hydrogen bonds|hydrogen bonds]], whereas G-C interactions consist of 3 intermolecular [[Hydrogen bonds|hydrogen bonds]]. These interactions form bridges between two DNA chains, thus creating a double stranded 'ladder' shaped structure. Each strand acts as a template for the other one in DNA replication. DNA is copied into [[MRNA|mRNA]] (messenger RNA) which carries the information from the original DNA template strand to be involved in protein synthesis.  The process of DNA being copied into mRNA is termed [[Transcription]] . The transcripted mRNA is then translated in a process called [[Translation]] by [[TRNA]].

Despite many other theories, in 1953 [[James watson|James Watson]] and Frances Crick discovered the true structure of a double stranded DNA molecule to be a 'Double Helix'. This was solved as a result of 'stick-and-ball' models they created, along with utilising the work of fellow scientists [[Rosalind Franklin|Rosalind Franklin]] and [[Maurice Wilkins|Maurice Wilkins]] on [[X-ray crystallography|X-ray crystallography]]<ref>http://nobelprize.org/educational/medicine/dna_double_helix/readmore.html</ref> . The [[X-ray diffraction|X-ray diffraction]] photographs obtained from [[DNA|DNA]] fibres, displayed a unique X-shape, which illustrates a helical stucture, although they indicated a repeating structure of 3.4 Å apart per turn of the helix, each base is roated 36 degrees from the next one. The diameter of the helix is 20Â. They found that the sugar-phosphate backbone was on the outside and the bases are positioned on the inside of the helix <ref>http://www.chm.bris.ac.uk/motm/dna/dna.htm</ref><ref>J.Berg, J.Tymoczko, L.Stryer;, 113-115, 2012 Freeman; Biochemistry</ref>. 

The DNA of the Indian muntjac which is an Asiatic deer has the longest length ( approximately 3 billion nucleotides) among all the known DNA molecules of other organisms.<ref name="null">Berg, J.M, Biochemistry, 7th ed, 2012:117</ref>

=== References ===

<references />

DNA

2013-11-16T14:55:17Z

130077415:

[[Image:BASE PAIRINGS.png|left|DNA Helix]]

DNA (deoxyribonucleic acid) is the genetic information found in the [[Nucleus|nuclei]] of most [[Organism|organisms]]. It is arranged into structures called [[Chromosome|chromosomes]]. The structure of DNA was first identified as having a 'double-helix' structure by [[Watson|Watson]] and [[Crick|Crick]] in 1953. DNA is composed of 4 [[Base|bases]]: the [[Purine|purines]]: [[Adenine|adenine]] (A) and [[Guanine|guanine]] (G); and the [[Pyrimidine|pyrimidines]]: [[Thymine|thymine]] (T) and [[Cytosine|cytosine]] (C) <ref>HARTL AND JONES,2009:41, GENETICS : ANALYSIS OF GENES AND GENOMES SEVENTH EDITION.</ref>. These form complementary base pairs of AT and GC. DNA also contains a [[Phosphates|phosphate]] group connected to a [[Deoxyribose sugar|deoxyribose sugar]]. The phosphate group is attached to the sugar through a [[Phosphodiester bond]].  

=== Structure of DNA ===

DNA is a chain of monormers (repeating units) called "nucleotides". A nucleotide consists of: a [[Deoxyribose|2` deoxyribose sugar]] (A five ([[Pentose|pentose]]) [[Carbon|carbon]] sugar  similar to that of [[Ribose|ribose]] sugar found in [[RNA|RNA]]. Its chemical formula is C5H10O4), a [[Phosphate group|phosphate group]] (contains one [[Phosphorus|phosphorus]] [[Atom|atom]], bonded to 4 [[Oxygen|oxygens]] and forms a [[Phosphodiester bond|phosphodiester bond]], which connects 2 [[Deoxyribose|deoxyribose sugars]] together resulting in the formation of a chain) and a base (one from A, C, G or T, which forms a side chain branching from the 2` deoxyribose sugar).

The 2` deoxyribose sugar/phosphate group region is regarded as the 'backbone' of DNA strands due to its structural purpose and the sequence of bases carries the gentic information. In order to produce a double stranded DNA structure, interactions occur between complementary bases. The complementary base pairs in DNA interact with one another via [[Hydrogen bonds|hydrogen bonds]]: A-T interactions consist of 2 intermolecular [[Hydrogen bonds|hydrogen bonds]], whereas G-C interactions consist of 3 intermolecular [[Hydrogen bonds|hydrogen bonds]]. These interactions form bridges between two DNA chains, thus creating a double stranded 'ladder' shaped structure. Each strand acts as a template for the other one in DNA replication. DNA is copied into [[MRNA|mRNA]] (messenger RNA) which carries the information from the original DNA template strand to be involved in protein synthesis.  The process of DNA being copied into mRNA is termed [[Transcription]] . The transcripted mRNA is then translated in a process called [[Translation]] by [[TRNA]].

Despite many other theories, in 1953 [[James watson|James Watson]] and Frances Crick discovered the true structure of a double stranded DNA molecule to be a 'Double Helix'. This was solved as a result of 'stick-and-ball' models they created, along with utilising the work of fellow scientists [[Rosalind Franklin|Rosalind Franklin]] and [[Maurice Wilkins|Maurice Wilkins]] on [[X-ray crystallography|X-ray crystallography]]<ref>http://nobelprize.org/educational/medicine/dna_double_helix/readmore.html</ref> . The [[X-ray diffraction|X-ray diffraction]] photographs obtained from [[DNA|DNA]] fibres, displayed a unique X-shape, which illustrates a helical stucture, although they indicated a repeating structure of 3.4 Å apart per turn of the helix, each base is roated 36 degrees from the next one. The diameter of the helix is 20Â. They found that the sugar-phosphate backbone was on the outside and the bases are positioned on the inside of the helix <ref>http://www.chm.bris.ac.uk/motm/dna/dna.htm</ref><ref>J.Berg, J.Tymoczko, L.Stryer;, 113-115, 2012 Freeman; Biochemistry</ref>. 

The DNA of the Indian muntjac which is an Asiatic deer has the longest length ( approximately 3 billion nucleotides) among all the known DNA molecules of other organisms.<ref name="null">Berg, J.M, Biochemistry, 7th ed, 2012:117</ref>

=== References ===

<references />

Enzyme

2013-11-15T14:46:51Z

130077415:

Enzymes <ref>Molecular Biology of the Cell 5th ed (2007) Alberts et.al. 159-169</ref> act as specific [[Catalysts|catalysts]]. That is to say each enzyme accelerates one or more specific chemical reactions without affecting the final [[Equilibrium|equilibrium]] concentrations of reactants and products, in addition the enzyme is never used up during the reaction it catalyses, and so is always available to catalyse more of the same reaction if needed. In [[Thermodynamics|thermodynamic]] language, enzymes reduce the [[Activation energy|activation energy]] of a reaction but do not affect the [[Free energy|free energy]] change of the overall reaction. Many enzymes are so effective that they will [[Catalyse|catalyse]] intracellular reactions which are too slow to be observed at all under comparable conditions in the absence of enzyme catalysis. Enzymes are often highly specific, both for the [[Molecule|molecules]] they will accept as [[Substrate|substrates]] and for the precise chemical changes that they will catalyse, and the presence of active enzymes is essential to form most of the [[Molecule|molecules]] in the [[Cell|cell]].

Enzyme reactions can be either [[Anabolic|anabolic]] or [[Catabolic|catabolic]] in nature <ref>Nigel P. O. Green (1989). Biological Science. 2nd ed. Cambridge: Cambridge University Press. p.167.</ref>.  

Enzymes and substrates must first interact to form an [[Enzyme-substrate complex|enzyme-substrate complex]] before any reaction can occur. This happens through molecular motions where all of the molecules in a cell are constantly moving and colliding; however only a few collisions will result in a reaction. Enzymes will remain unchanged after catalysing the reaction. The rate of encounter between the enzyme and the substrate is primarily dependant on the concentration on the substrate; meaning that, to increase the enzyme activity you must increase the substrate concentration. 

=== The mechanism of Enzyme Action: ===

Enzymes increase the rate of reaction between 2 reactants in various possible ways:

*They improve the Proximity of the substrate being that they increase the local concentration of the substrate
*They affect the orientation and hold the [[Atom|atoms]] in positions that favour the reaction
*They produce strain distortion; they put strains on the bonds that are associated with the reaction
*In acid-base catalysis they aid in the exchange of H+ or generation of –OH <ref>Molecular Biology of the Cell 5th ed (2007) Alberts et.al. 159-169</ref>
*They provide an alternative route of reaction with a lower activation energy

=== Specificity ===

Enzymes are specific to the point of being able to distinguish between optical isomers.

The [[Amino acids|amino acids]] forming the active site mainly determine the specificity of the enzyme; a change in only a few [[Amino acids|amino acids]] in this region can result in a large change in the shape of the active site and this could then vastly change to affinity for the substrate or even change the substrate the enzyme is specific for. 

The specificity of enzymes is exhibited in the ‘Lock and Key’ mechanism: 

 

[[Image:Lock and key.jpg]] 

 

Taken from [http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=stryer&part=A1031 http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=stryer&part=A1031] <ref>http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=stryer</ref>

This illustrates the Lock and Key mechanisms and how the shape of the substrate is exactly complememtary to the shape of the active site. However the lock and key model doesn't fully explain enzymatic activity. The model indicates that the enzyme and substrate are unable to change shape.

A modification to the Lock and Key Model of enzymes is the Induced Fit Hypothesis, also known as the "Hand-shake Model" <ref>http://www.portlandpress.com/pp/books/online/glick/searchresdet.cfm?Term=induced-fit%20theory%20%28rack%20model%29</ref>. This hypothesis states that the structure of both the enzyme and substrate can change on binding. In essence the enzyme can wrap itself around the substrate molecule, untill the substrate is completley bound. This produces an enzyme-substrate complex, which places strain on a particular bond, therefore weakening said bond; to a point where it can interact with the enzyme amino acid groups, further non-organic groups or further bound substrates.

The change in the shape of the enzyme is known as a conformational change; the purpose of which is two fold:

#As mentioned above, the conformational change places strain on the desired bond, allowing for a more efficient reaction to take place,
#The new conformation brings amino acid groups essential to the enzyme reaction, which in the unbound conformation may distant from the active site, into the active site. These groups ensure the catalytic reaction will be optimal <ref>The World of the Cell, 3rd Edition, (1996) Becker et.al. p146, p147</ref>. The most common groups to be brought into the Active Site of the Enzyme are those relating to Acid/Base chemistry - therefore promoting the reaction and ensuring optimal conditions <ref>The World of the Cell, 3rd Edition, (1996) Becker et.al. p146</ref>.

=== Substrates and the Active Site ===

Whether an enzymatic reaction will occur is dependant on the substrate colliding and binding to the active site. Once a substrate binds onto the active site, it is held there by a variety of interactions. These interactions take place between charged residual groups of the amino acids in the conformed active site. Hydrogen Bonds and Ionic bonds generally occur - however they are very weak. These weak interactions are of the order of '''3 - 12 kcal mol-1 (12.5 - 50.2 kJ mol''''''-1'''''') '''<ref>Royal Society of Chemistry [RSC]fckLRfckLRhttp://www.rsc.org/ebooks/archive/free/SP9780851869209/SP9780851869209-FP015.pdf</ref> this is of the order of 1/10th the strength of an, on average, single covalent bond <ref>The World of the Cell, 3rd Edition, (1996) Becker et.al. p146</ref>. 

This ensures that enzyme-substrate formation is a reversible process.

=== Allostery ===

An allosteric enzyme couples the effector levels to enzyme activity; it couples signal to functionality. Allosteric enzymes have multiple binding sites (allosteric sites) and show cooperative binding <ref>J.Mol.Biol. (2004) 336, 263-273</ref>.

Allosteric control of enzymes can be positive or negative and can have effects such as up regulate or down regulate activity.

Types of Allosteric control:

#Homotropic - The modulator is a substrate for the target enzyme aswell as the egulator e.g. Oxygen acting on Haemoglobin.
#Heterotropic - The modulator is the regulatory molecule but is not also the enzymes substrate. 

=== Enzyme Types ===

There are many enzymes used in labs, each has it's own unique active site and so will catalyse a specific reaction. Restriction enzymes are one type of enzymes that are frequently used.

Restriction [[Endonucleases|endonucleases]] are used naturally in a wide range of [[Prokaryotes|prokaryotes]] as a self-defence mechanism against foreign [[DNA|DNA]] [[Molecule|molecules]].  The prokaryotes own [[DNA|DNA]] is methylated so it will not be cut by the enzyme.They recognise a specific 4-8 base pair [[Palindromic sequence|palindromic sequence]] and by carrying out a hydrolysis reaction cut at that specific point. They may cut to form a blunt end or a sticky end. A blunt end is when the enzyme cut the [[DNA|DNA]] symmetrically. Asymmetrical cleavage leaves sticky end, these are unpaired bases. These sticky end can anneal to complementary bases on another strand <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman</ref>. 

=== Kinetics ===

Kinetic parameters:

Two important enzyme parameters in a simple enzyme catalysed reaction are the [[Michaelis-Menten constant|Michaelis-Menten constant]] ([[Michaelis-Menten constant|K]][[Michaelis-Menten constant|m]]) and the [[Maximum reaction|maximum reaction]] velocity ([[Maximum reaction|V]][[Maximum reaction|max]])

*Km is the approximate measure of the enzyme affinity for the substrate. This can be calculated from the graph as ½ Vmax. Generally a lower Km value signifies a higher affinity for the substrate.
*Kd is the dissociation constant for substrate binding to enzyme
*Kcat is the turnover number for the enzyme
*Vmax is the maximal activity of the enzyme when all of the active sites are saturated.

The michaelis-menten equation:

 V = Vmax [S]/Km [S]

 To obtain Vmax and Km the enzyme activity must be recorded and then plotted on a double reciprocal plot, a [[Lineweaver-Burk plot|Lineweaver-Burk plot]], and the Michaelis Menten equation is then rearranged to look like this: 1/V = (Km/Vmax)(1/S)+1/Vmax <ref>Molecular Biology of the Cell 5th ed (2007) Alberts et.al. 159-169</ref>.

[[Image:350px-Lineweaver-Burke plot svg.png]] 

Taken from [http://www.search.com/reference/Lineweaver-Burk_plot www.search.com/reference/Lineweaver-Burk_plot] <ref>http://www.search.com/reference/Lineweaver-Burk_plot</ref> A Lineweaver-Burk plot showing all the necessary parameters. 

=== Inhibition ===

Enzymes can be inhibited by denaturing which is when a protein is changed in structure to form a randomly coiled peptide which exhibits none of its usual functions. Denaturing can result from extreme temperatures and [[PH|pHs]], as these alter the bonding in the molecule.

Inhibition can also be initiated by the binding of specific molecules called inhibitors. These can be split into categories:

#Irreversible Inhibitors are molecules that permanently bind to the enzyme's active site or specific side chain, commonly to the serine (CH2OH) or cysteine (CH2SH) by [[Covalent|covalent]] bonds. Thsi inactivates the enzyme so the substrate cannt bind.
#Competitive Inhibitors are competing molecules that will have a very similar structure to that of the natural substrate and thus will be complementary to the enzyme active site. Vmax stays the same, but Km increases This type of inhibition can be overcome by an increase in substrate concentration.
#Non-competitive inhibitors bind to a region on the enzyme other than the active site, causing changes to enzyme shape resulting in disruption of the active site. This decreases the turnover number of the enzyme rather than preventing substrate binding- Vmax decreases but Km stays the same. This cannot be overcome with an increase in substrate concentration.
#Uncompetitive inhibitors only bind to an enzyme-substrate complex; so both Km and Vmax decreaae as it takes longer for the substrate to leave the active site. This also cannot be overcome by an increase in substrate concentration. We are able to distinguish the types of inhibition occurring by looking at the graph of enzyme activity <ref>Biochemistry 6th (2006) Stryer et.al. pg51</ref>.

[[Image:Inhibitor graph.jpg]] Taken from [http://ibhow.files.wordpress.com/2010/06/7-6-4.jpg?w=399&h=275 http://ibhow.files.wordpress.com/2010/06/7-6-4.jpg?w=399&h=275] <ref>http://ibhow.files.wordpress.com/2010/06/7-6-4.jpg?w=399&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;h=275</ref>

Competative Inhibitors show the same Vmax value however we see an increased Km value and non-competitive inhibitors show a decreased Vmax but the same Km. 

=== Targets for drug action ===

We are able to exploit these mechanisms of inhibition to engineer drugs with therapeutic effects. By targeting an enzyme in drug therapy we have the ability to change whole metabolic reactions that are catalysed by that particular enzyme. We can investigate possible new drugs by exploring drug-reaction interactions and drug-pathway interactions <ref>BMC Bioinformatics 2010, 11:501</ref>.  Some examples of Drug Inhibitors:

*Irreversible drug inhibitors: [[Penicillin|Penicillin]] the antibiotic which inhibits transpeptidate in bacteria rendering them unable to synthesise cell walls. Aspirin which decreases the inflammatory response by inhibiting Cyclooxegenase.
*[[Competitive inhibitors|Competitive inhibitors]]: Methotrexate which inhibits dihydrofolate reductase which is involved in the synthesis of [[Purine|purines]] and [[Pyrimidine|pyrimidines]].
*[[Non-competative inhibitor|Non-competitive inhibitor]]: NNRT1 in the treatment of HIV <ref>Biochemistry 6th (2006) Stryer et al.</ref>. 

=== References ===

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