Metabolic pathways
Metabolic pathways consist of chains and cycles of enzyme-catalyzed reactions.
Metabolic pathways consist of chains and cycles of enzyme-catalyzed reactions.
Induced-fit model
When enzymes and substrates bind, active
site is not completely rigid and may undergo conformational change in shape to
better fit substrate. Structure of substrate is also altered, changed in
traditional state. Changes help weaken + break bonds in substrate and lower
activation energy and catalyze reaction.
Enzymes lower activation energy
Enzymes speed rate of biochemical reaction by lowering activation energy. Binding of substrate to enzyme lowers overall energy level of transition state, activation energy is therefore reduced.
Enzymes speed rate of biochemical reaction by lowering activation energy. Binding of substrate to enzyme lowers overall energy level of transition state, activation energy is therefore reduced.
Difference between competitive and non-competitive inhibition
Competitive inhibition: inhibitor is
structurally and chemically similar to substrate and binds to active site of
enzyme; prevents substrate from binding; increasing concentration of substrate
overcomes.
Example: oxygen competing with carbon dioxide
for active site for Rubisco.
Non-Competitive inhibition: molecule not
structurally and chemically similar in structure to substrate reacts with bulk
of enzyme, reducing accessibility of active site; increasing concentration of substrate
cannot overcome.
Example: Cyanide ions blocking cytochrome
oxidase in terminal oxidation in cellular aerobic respiration.
End Product Inhibition (ibbio.ninja.com.au)
Metabolic pathways by end-product inhibition
End product inhibition form of negative
feedback - increased levels of product decrease rate of product formation;
product can regulate rate of own production by inhibiting an earlier enzyme in
the metabolic pathway.
- Product binds to allosteric site of
enzyme (non-competitive inhibition).
- Enzyme non-functional - rate of product
formation will decrease (less product comes less enzyme inhibition).
Example: ATP formation by
phosphofructokinase (enzyme glycolysis); ATP inhibits phosphofructokinase, so
when ATP levels are high, glucose is not broken down (stored as glucose).
- When ATP is low, phosphofructokinase is
activated and glucose is broken down to make more ATP.
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