CBI6 - Enzymes and Kinetics of Biocatalysis Flashcards
Define basic mechanism of an enzyme substrate reaction.
Enzyme and substrate bond to form enzyme-substrate reaction. Following this a product is released leaving the enzyme ready for re-use.
Define notation for Gibbs activation energy.
Delta G with transition state symbol.
Discuss how a catalyst works.
Lowers activation energy by providing alternative pathway. Not used up itself so can be reused.
Which enzymes are not proteins.
Ribozymes - enzymes made up RNA not a protein.
How can you define an irreversible reaction by Gibbs energy.
Largely negative change in Gibbs energy.
How many numbers are used for enzyme classification.
4 numbers.
Discuss kinetics of enzyme catalysed reaction with no inhibitor at low and high substrate concentration.
Low [S] - first order - directly proportional.
High [S] - zero order - no proportionality.
Define Vmax.
Maximum velocity of enzyme reaction when all enzymes are saturated with substrate. Approached but never reached.
Define kcat.
No. Of substrate molecules that are turned over by enzymes in a second.
Define Michaelis Menten equation.
V = Vmax[S]/(Km + [S])
Is Km the same for all enzymes and what is it.
Different for each enzyme but is independent of [E].
Km is [S] needed to reach half Vmax
What does a low Km indicate.
High affinity of enzyme for the substrate.
How can a Lineweaver Burk ploy be obtained from the Michaelis Menten equation.
Taking double reciprocal forming linear equation in y=Mx+c format.
What formula can be used to describe catalytic efficiency.
Kcat/Km.
What factors are taking into consideration with catalytic efficiency.
Combines catalytic potential with the ability to bind substrate at low [S].
Name three types of inhibitor.
Competitive. Uncompetitive. Non-competitive.
What is the difference between reversible and irreversible enzyme reactions.
Formation of temporary bonds vs permanent covalent bonds.
Discuss effects of a competitive inhibitor.
Binds to active site of enzyme. Degree of inhibitor depends on [S]. Effect of inhibitor can be overcome by increasing [S].
Discuss effects of uncompetitive inhibitors.
Binds to E-S complex. Prevents release of product. Cannot be overcome by increasing [S].
Discuss effects of non-competitive inhibitor.
Binds at allosteric site of enzyme. Prevents enzyme from carrying out its catalytic function.
What is an enzyme cofactor.
Small non protein chemicals or metals. Aid function of enzyme. Commonly drives from vitamins.
How do the active sites of enzymes aid the function of enzymes as catalysts.
Active sites lower activation energy by stabilising the transition state.
Give numbers and associated class names for first number of enzyme classification.
- Oxidoreductases.
- Transferases.
- Hydrolases.
- Lyases.
- Isomerases.
- Ligases.
What is km.
(K-1 + k2)/k1 where:
K-1 = ES -> E + S
K2 = ES -> P
K1 = E + S -> ES
What combination of kcat and km gives highest efficiency of enzyme.
Larger kcat and smaller km
How do competitive inhibitors affect Km and Vmax.
Vmax remains same.
Km increases.
How do uncompetitive inhibitors affect Vmax and Km.
Vmax decreases.
Km decreases.
How do non competitive inhibitors affect Vmax and Km.
Vmax is decreased
Km remains same
What are two conditions affecting enzymes.
Temperature and pH.
How does pH affect enzymes.
Enzymes have own optimal pH. Too high or too low means it will be denatured.
How does temperature affect enzyme.
Optimum temperature needed. Temperature too high breaks bonds in enzyme causing it to become denatured.
Give types of reversible covalent modifications.
Phosphorylation, acetylation, methylation, carboxylation.
Give name of enzyme that adds phosphate group to a molecule.
Kinase.
Give type of enzyme that removes phosphate group from molecule.
Phosphatase.
Define an allosteric inhibitor.
Inhibitors that act on enzymes by binding to the allosteric site.
Which type of inhibitor is always an allosteric inhibitor.
Non competitive inhibitors are all allosteric inhibitors.
What effect on enzyme activity can allosteric inhibitors have.
Either cause inhibition of enzyme activity or activation of enzyme activity.
How do allosteric inhibitors work on enzyme activity.
Upon binding, cause conformational change which either gives correct active site (activating enzyme) or distorts active site (inhibiting enzyme).
What graph shape is obtained for allosteric enzymes and discuss enzyme kinetics.
Sigmoidal. At low [S], very gradual increase in velocity. One substrate binds to enzyme causing conformational change allowing more substrate to bind. Eventually all sites become saturated. Graph plateaus.
Give examples of enzyme following allosteric sigmoid shape.
Haemoglobin binding to oxygen.
