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Enzymes lecture notes
The Human Body (PY4010)
Kingston University
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Enzymes (N) 1
Enzymes (N)
Enzymes Proteins that speed up (catalyse) specific chemical reactions. Enzyme defects cause disease. Functions of enzymes Digestion, blood clotting, defence, movement and nerve conduction. Types of enzymes Proteases ⇒ enzymes that break down proteins Nucleases ⇒ enzymes that break down nucleotides Polymerases ⇒ enzymes that synthesise long chains of polymers Kinases ⇒ adds phosphate groups to other molecules Key enzyme properties Increase reaction rate Show specificity Unchanged at end of reaction Do not alter reaction equilibrium Reducing the free energy of activation (△G) These properties Provide a reaction of lower energy and bring molecules together in the active site. As well as preventing substrate movement and straining bonds in the substrate to make breakage easier. Enzymes are drug targets Antibiotics e. penicillin ⇒ inhibit cell wall synthesis Anti-inflammatory agents e. aspirin ⇒ blocks prostaglandin synthesis Anticancer drugs e. methotrexate ⇒ interferes with synthesis of DNA precursors The active site
Enzymes (N) 2
A 3D cavity/cleft that binds specifically to a substrate(s). Formation of an enzyme-substrate (ES) complex at the active site is the first step in enzyme catalysis. Evidence for active sites comes from X-ray crystallography and kinetic studies of enzyme activity. Lock-and-key model The enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. Enzymes are highly specific. Induced fit model Both the substrate and the active site of the enzyme change in conformation until the substrate is completely bound to the enzyme, at which point the final shape and charge is determined. This activates the enzyme into performing its catalytic function. Most enzymes work via induced fit. Km and Vmax Km is the substrate concentration which is equal to half its maximum value. Vmax is the point where all the active sites are bound to substrate.
Competitive inhibition Decreases rate of reaction ⇒ similar shape to substrate ⇒ competes for active site so substrates can’t bind ⇒ fewer E-S complexes. Increasing substrate concentration reduces effect of inhibitor. Km is increased and Vmax is unaltered. Non-competitive inhibition Decreases rate of reaction ⇒ binds to site away from the active site (allosteric site) ⇒ the active site changes shape so substrate can’t bind ⇒ fewer E-S complexes. Increasing substrate concentration has no effect on rate of reaction as causes permanent change to active site. Km is unaltered and Vmax is reduced.
Enzymes lecture notes
Module: The Human Body (PY4010)
University: Kingston University
