Enzymes 2 Flashcards
How are enzyme reaction rates no longer limited by the chemical steps?
Evolution has acted on it
What is now the limiting factor of enzyme reaction rates?
Limited by diffusion rates
What is k1?
The binding step
What is k3?
The conversion of the substrate to its product and the release from the active site
Give the method for proof on the limiting factor reaction of enzymes
Put enzyme and a small amount of substrate and follow the ROR to make the enzyme and product
Why cant you do the enzyme reaction with big amounts of substrate?
The substrate will be bound up in E-S complexes so you’d be measuring the K3 not the K1
What would affect the ROR if the binding was the limiting factor?
Viscosity of the solution
How could you change the viscosity of a solution?
Add glycerol
What should the intrinsic rate constant be for a diffusion-limited reaction?
10^8
How else can you find out whether an enzyme reaction is diffusion limited (not practical)?
Through theoretical calculations
What do you need to take into account when working out the intrinsic rate constant of an enzyme recation?
The size of the substrate and the enzyme
What is one of the best understood examples of a perfect enzyme?
Triose phosphate isomerise
In glycolysis, what is the conversion of the C-6 molecule to 2x C-3 molecules catalysed by?
Aldenase
What does triose phosphate isomerase do in glycolysis?
Converts the dihydroxyacetone phosphate and the glyceraldehyde 3-phosphate meaning that both can be fed down the glycolytic pathway
Which proteases hydrolyse peptide bonds?
Serine, cysteine, aspartyl and metallo-proteinases
How do serine proteases break peptide bonds?
The very reactive serine attacks the peptide bond to form an acyl-enzyme
Which residue in chymotrypsin is a serine?
195
How does residue 195 on chymotrypsin react with the peptide bond?
Forms an acyl bond intermediate which can be hydrolysed very easily. This results in the cleavage of the peptide bond
What is a catalytic triad?
Constellation of active side groups which come together to make the serine very reactive
Why don’t serine proteases cleave all of the peptide bonds?
They have a sequence specificity that is determined by the nature of the residue on the N-terminal side of the peptide bond that will be cleaved
When will chymotrypsin cleave peptide bonds?
When the asterisked residue is a phenylalanine, tryptophan or tyrosine
What is the same about all of the chymotrypsin asterisked residues?
Hydrophobic
