Enzymes I Flashcards
What are some functions of enzymes? [5 marks]
- Digestion
- Blood clotting
- Defence
- Movement
- Nerve conduction
What causes phenylketonuria? [1 mark]
Reduced levels of the enzyme phenylalanine hydroxylase.
What processes can be affected in glycogen storage diseases? [3 marks]
- Glycogen synthesis
- Glycogen breakdown
- Glycolysis
What happens in Tay-Sachs disease and what causes it? [2 marks]
- Cerebrosides build up in the brain.
- This is caused by insufficient activity in hexosaminidase A.
What does penicillin inhibit? [1 mark]
Cell wall synthesis
What does aspirin block? [2 marks]
- Cyclooxygenase (COX)
- This is involved in the synthesis of prostagladins.
How does methotrexate help treat cancer? [2 marks]
- Inhibits dihydrofolate reductase (which is needed to produce a folic acid precursor)
- Prevents thymine from being made and prevents DNA synthesis in cancer cells.
What are the key properties of enzymes? [5 marks]
- Increases reaction rate
- Specific
- Unchanged at the end of reactions
- Doesn’t alter reaction equilibrium
- Decrease the free energy of activation
When is free energy at its highesr? [1 mark]
At the transition state.
What does the lock and key model explain and what does it fail to explain? [2 marks]
- Explains specificity
- Doesn’t explain stabilisation of the transition state.
What does the induced fit model explain? [2 marks]
- Specificity
- Stabilisation of the induced fit (via confirmational change of the active site)
What is the binding energy? [1 mark]
The free energy that is released by the formation of weak interactions between a substrate and enzyme.
What is the binding energy used for? [5 marks]
- Freeze the substrate in place
- Stabilise charges in the transition state
- Provide a reaction pathway with a lower energy
- Strain specific bonds in the substrate
- Use cofactors
What is V-max? [2 marks]
- Maximum initial velocity
- Unit: μmol/min
What is Kcat/K3? [2 marks]
- The turnover number
- Divide V-max by the number of enzymes to get this
What is Km? [2 marks]
- Michaelis constant
- Substrate concentration at half V-max
How is the V-max and Km affected with a competitive inhibitor? [2 marks]
- V-MAX: Unaffected
- Km: Decreased
How is the V-max and Km affected with a non-competitive inhibitor? [2 marks]
- V-max: Decreased
- Km: Unaffected
How is enezyme activity regulated? [5 marks]
- Control of gene expression
- Control of amount of enzyme
- Compartmentalisation
- Covalent modification to change enzyme shape and activity
- Allosteric modification
Do allosteric enzymes demostrate Michaelis-Menten kinetics and why/why not? [2 marks]
- No (V v. S plots are sigmodal)
- Effectors binding to allosteric regions affect enzyme activity
What is the definition of feedback inhibition? [1 marks]
When the product of a pathway inhibits enzymes involved in its synthesis.
What is ATCase? [1 mark]
Aspartate Carbamoyl Transferase is involved in the synthesis of pyrimidine.
What is the structure of ATCase? [4 marks]
- 12 catalytic subunits with active sites
- 6 catalytic subunits form a hemisphere (2 in total)
- 6 regulatory subunits
- regulatory dimers hold catalytic hemispheres together
What happens when cytidine triphosphate binds to ATCase? [1 mark]
Catalytic hemispheres come together
