Seminar 8: Enzymes & Energy Flashcards
what is the catalytic unit
polypeptide in quaternary structure with the active site
what is the regulatory unit?
polypeptide in quaternary structure with the allosteric site
why does reaction rate speed up as sites become sequentially activated? (Enzymes w/ subunits w/ own active sites)
when enzymes have multiple subunits w/ active sites:
1. binding to 1 active site causes ALLOSTERIC effects (slight change in protein structure)
2. this influences the adj subunit, making it MORE LIKELY to bind to substrate
how does a cell stop a metabolic pathway if they no longer need a product?
- have the final product of the pathway inhibit the enzyme that catalyses the commitment step (often allosterically, non-competitive inhibitor)
AKA feedback inhibition/end-product inhibition
the synthesis of cholesterol involves a biochemical pathway that begins w/ HMG-CoA reductase. Statins are drugs that are widely used to inhibit cholesterol synthesis/ How do you suppose statins work?
- statins bind to the enzyme, inhibiting it
- substrate can no longer bind, prevents enzyme from catalysing the reaction
- pathway to synthesise cholesterol cannot progress, decreases synthesis
how to inactivate most enzymes after they’ve been activated?
- reverse phosphorylation
- protein phosphatase catalyse hydrolysis & removal of phosphate grp so that enzyme is inactive again
inside the cell, pH of cytosol ~ 7.2, but in lysosome ~ 4.8. A protease which catalyses hydrolysis of proteins is active w/in lysosome but inactive in cytosol. How can this occur?
- Due to compartmentalisation, different parts of a cell can have different internal environ
- protease has an optimal pH range w/in acidic conditions therefore it can only func in pH<7
- in the cytosol, protease would denature, there would be a change in its 3D tertiary shape due to change in ionisation of R-grps &/or carboxyl & amino grps
what happens to carboxyl grps in neutral/basic pH?
COOH looses H+ & becomes COO-
what happens to amino grps in neutral/acidic pH?
NH2 accepts H+ & becomes NH3+
how are polysaccharides broken down for energy?
- hydrolysed to glucose
- glucose passes through glycolysis & cellular respiration
- energy captured as ATP
how are lipids broken down for energy?
- hydrolysed into F.A & glycerol
- Glycerol converted to dihydroxyacetone phosphate (DHAP) - intermediate in glycolysis
- F.A reduced to molecules that are converted to acetyl CoA - in mitochondrion, by series of oxidation enzymes (beta-oxidation)
- Acetyl CoA enters citric acid cycle, catabolised to CO2
how are proteins broken down for energy?
- hydrolysed into A.A
- feed into glycolysis or citric acid cycle @ diff points depending on their structures
what is gluconeogenesis
metabolic process that creates glucose from non carbohydrate sources (A.A, glycerol etc)
what is Acetyl CoA form?
- pigments
- plant growth substances
- steroid hormones
- rubber
how to regulate each step in a biochemical pathway?
- changing amount of active enzyme : cell can increase expression of gene encoding an enzyme
- changing enzyme activity by covalent modifications : adding phosphate grps by kinase can alter enzyme activity
- feedback inhibition : final product allosterically binds to enzyme, inhibits it
- substrate availability : if substrate used by another enzyme, 1st one can’t function anymore, pathway shuts down
