Enzymes II Flashcards
What are perfect enzymes? [1 marks]
Enzymes where the reaction is so efficient that the reaction rate is limited by diffusion of the substrate.
Why can’t all enzymes in the body by perfect? [1 mark]
All of the energy would be burnt up for metabolism.
How can you make a reaction from a perfect enzyme more efficient? [1 mark]
Make all the transition state energies as high as the diffusion step.
What is trypsin’s binding pocket like? [3 marks]
- The binding pocket is negative to attract positive amino acid residues (e.g. lysine, arginine)
- Positive side chains are very long so they reach into a pocket.
- This stabilises binding of the side chains.
What is chymotrypsin’s binding pocket like? [1 mark]
- Hydrophobic pocket to attract aromatic rings.
What is elastase’s binding pocket like? [2 marks]
- Narrow opening
- So only small amino acids can bind to it.
What’s the difference between catalysed and non catalysed proteolysis with serine proteases? [2 marks]
CATALYSED: Serine’s OH is attacking the peptide bond before the water does.
NON-CATALYSED: Water has to come directly to attack the peptide bond.
How is ATP synthesised? [2 marks]
- Via a proton driven rotary ATP synthase
- Because the inner membrane is impermeable to protons.
Structure of ATP synthase [2 marks]
- 3 active sites activated by a rotating spindle
- Central core has 6 subunits held together by a protein complex
What is the purpose of topoisomerase II and what would happen without it? [2 marks
- Enzyme that unlinks tangled chromosomes.
- Without this, chromosomes would fragment.
How does topoisomerase II work? [4 marks]
- Binds to a chromosome and makes the double strand break in one chromosome.
- Passes DNA through the chromosome.
- ATP binds to the binding sites of a clamp.
- When ATP is hydrolysed, the clamp opens.
