Enzymes Flashcards
What is a transition state?
An unstable, high energy intermediate in a chemical reaction. Stabilising the transition state in one way that enzymes can speed up a reaction.
What is chymotrypsin?
An endopeptidase, it catalyses the cleavage of an internal peptide bond within a polypeptide chain.
What substrates does chymotrypsin prefer to bond with?
Substrates where the carboxyl group is presented by an amminoacid with an aromatic side chain.
What does aspartate do in the catalytic triad of chymotrypsin?
Forces histidine to be in the right orientation and tautomeric form by creating a strong hydrogen bond
What is substrate specificity?
Shape of the pocket next to the catalytic site determines substrate preferences. Some cannot accommodate big bulky side chains
Enzymes will usually:
-Catalyse only one type of reaction and act on only a few related molecules
What will the substrate alcohol dehydrogenase catalyse?
Oxidise primary alcohols to aldehydes
What do hydrolases catalyse?
Formation of two products from a substrate for hydrolysis.
-Example= trypsin
What do lyses catalyse?
Non hydrolytic addition or removal of groups from substrates
- example= aldolase
What weak bonds are enzymes structures stabilized by?
H-bonds, electrostatic salt bridges, van der waals and hydrophobic interactions
What are the effects of a change in pH on the enzyme?
- Unfolding of the enzyme- complete inactivation
- changes in ionization state of active site residues leading to changes in Km and Vmax
What is a typical enzyme that causes pH changes?
Pepsin in stomach acid
What is hyperbolic kinetics?
At low substrate concentration, the reaction rate is directly proportional to substrate.
-At high concentration, the reaction rate is independent of substrate concentration
(pic)
What is the best way to compare catalytic efficiency?
Report the ratio between Kcat and Km
What do competitive inhibitors increase?
Km, do not alter Vmax
