enzymes

Question 1

define hydrolases

Answer 1

general term for enzymes that catalyse hydrolytic cleavage reactions
nucleases (break down nucleic acids) and proteases (“ proteins) are subsets

Question 2

define kinases. what enzyme has the opposite function?

Answer 2

enzymes that catalyse the addition of phosphate groups to molecules
phosphatases do the opposite - hydrolytic removal of phosphate group

Question 3

how are ligands bound to enzymes?

Answer 3

by many weak bonds at the active site. selectivity and affinity to a ligand depends on the formation of these weak bonds.

Question 4

how can proteins have catalytic properties?

Answer 4

neighbouring chemical groups on their surface interact in ways that enhance the chemical reactivity of amino acid side chains

Question 5

two ways that chemical groups on proteins interact to enhance chemical reactivity

Answer 5

1. restrict water access to protein-ligand binding site - because water easily forms H-bond that compete
2. clustering polar amino acid chains - eg. cluster of -ve, greater affinity for +vely charged ligand

Question 6

how do enzymes speed up reactions?

Answer 6

by selectively stabilising transition states (by increasing local conc of substrate or holding atoms in correct orientation)
the highest energy transition state determines activation energy and hence ROR

Question 7

function of a lysozyme and how it works

Answer 7

destroys bacterial cell walls by hydrolysing sugar linkages in peptidoglycan

Question 8

substrate and products of lysozyme catalysis

Answer 8

substrate: 6-sugar oligosaccharide

product: 4-sugar oligosaccharide + disaccharide (ie. sugar link hydrolysed)

Question 9

steps in lysozyme catalysis

Answer 9

1. substrate binding (lysozyme attaches to cell wall, distorts polysaccharide residue)
2. Covalent catalysis (cleave C-O bond)
3. Covalent intermediate
4. Water binding (hydrolysed, residues released)

Question 10

side chain present in active site of lysozyme

Answer 10

Asp 52

Question 11

what is the catalytic triad found in many serine proteases?

Answer 11

Asp, His, Ser
aspartic side chain, histidine, serine

Question 12

Asp / His / Ser catalytic triad mechanism

Answer 12

Asp induces the Histidine to remove the proton from Serine, activating it so that it has a -ve on the O

(basically, H bond rearrangements –> reactive serine can react with a ligand)

Question 13

describe the activity profile of an enzyme as pH changes

Answer 13

a bell shaped curve - greatest activity and stability in the middle
low pH = lots of protons, proteins positively charged
high pH = lots of hydroxyl ions, proteins negatively charged

Question 14

define coenzyme