Lecture 3: Enzymes Flashcards
1
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enzymes
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biological catalyst that speed up a chemical reaction without being consumed in the process
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chemical nature
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they are globular proteins except for a small group of RNA molecules
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properties of enzymes
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- are not consumed in reactions
- highly specific
- reaction catalysed is reversible
- do not affect equilibria of reaction
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mechanism
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- speed up a reaction by providing alternative pathway of reaction with lower activation energy facilitating formation of transition state
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Gibbs free energy(ΔG’)
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difference in free energy between the transition state and substrate state
aka activational barrier
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endorgenic reaction
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- does not release free energy
- requires input of energy to proceed
- +ΔG
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exergonic reation
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- -ΔG
- gives off free energy
- reaction is spontaneous i.e proceeds without input of energy
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ΔG=0
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reaction is in equilibrium
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Active site
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- 3D cleft lined with amino acid residues that are critical in making and forming bonds, binding to a substrate ligand
- where the transition state occurs
- takes a small part of the enzyme
- H bonds, electrostatic forces, VDW forces and hydroohobic interactions
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Thermodynamic equation
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ΔG=ΔG*’ +RTln[prod]/[reactants]
* Keq=[prod]/[reactants]
R= 1.987×10^-3Kcalmol-1k-1
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Lock and key model
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- active site is lined up with amino acid residues complementary to the subrate in terms of shape size, charge
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Nonfunctional enzymes
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- arise from destruction of cells, leukocytes, erythrocytes etc
- tissue damage or disease is accompanied by increase of these
- hence they can aid in diagnosis
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Induced fit model
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- exposure of enzyme to the substrate induces a conforational change in enzyme
- changing the shape of active site
- allowing substrate and eznyme to bind tightly
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functional enzymes
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refers to enzymes of known physiological function which are produced by the liver
lipoprotein lipase, pseudo cholinsterase
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