web_L25_08BIO311C - BIO 311C March 24, 2008 A large...

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BIO 311C March 24, 2008
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A large fraction of all chemical reactions that occur in cells fall into one of four broad categories: Protonation / de-protonation * isomerization Hydrolysis / dehydration oxidation-reduction * * Protonation and de-protonation reactions are sometimes not treated as chemical reactions since they require the movement of only a single proton. However, the protonated and de-protonated forms of functional groups have very different physical and chemical properties, and therefore act very different from each other biologically. Thus, in this course we will consider protonation and de-protonation processes to be chemical reactions.
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Example of a Protonation / De-protonation: de-protonation (a half-reaction) protonation (a half-reaction) Protonation/de-protonation reactions do not need an enzyme to proceed very rapidly. A protonation half-reaction always must be coupled to a de-protonation half- reaction in order to produce the complete reaction. complete reaction * Sum of the 2 half-reactions
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Example of an Isomerization: D-glyceraldehyde (an aldotriose) dihydroxyacetone (a ketotriose) C 3 H 6 O 3 C 3 H 6 O 3 isomerase * I somerase enzymes rearrange atoms in a substrate molecule, but do not change the atomic composition of the molecule. i.e. the chemical formula of the molecule is not changed. Most isomerization metabolic reactions require an isomerase enzyme in order to proceed.
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Example of a Hydrolysis/Dehydration: glucose + P i glucose-6 -P + H 2 O hydrolysis dehydration glucose-6-phosphatase Dehydration reactions are the reverse of hydrolysis reactions. Most dehydration/hydrolysis metabolic reactions require an enzyme in order to proceed at a reasonably rapid rate. * + + glucose-6-phosphatase This dehydration reaction is endergonic. Thus its reverse, a hydrolysis, is exerbonic. An alternative way of illustrating the reaction shown above:
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e - A molecular species is said to be oxidized if it loses one or more electrons.
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web_L25_08BIO311C - BIO 311C March 24, 2008 A large...

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