Chapter 8

Question 1

what are four basic catalytic strategies used by many enzymes?

Answer 1

covalent catalysis; general acid base catalysis; metal ion catalysis; catalysis by approximation and orientation

Question 2

many isolated enzymes if incubated at 37 degrees C will be denatured. however, if the enzymes are incubated at 37 degrees C in presence of substrate the enzymes are catalytically active. explain paradox.

Answer 2

3D structure of enzyme is stabilized by interactions with substrate, reaction intermediates, and products
stabilization minimizes thermal denaturation

Question 3

How can group specific reagents be used to determine the mechanism of action of an enzyme?

Answer 3

if particular amino acid side chain suspected of participating in catalytic mechanism, covvalent modification of residue by group specific reagent may alter it sufficiently that the enzyme activity is altered/inhibited

Question 4

Competitive Inhibition

Answer 4

vmax remains same but kmapp increases, sulfanilamide, inhibitor binds at substrate

Question 5

Uncompetitive Inhibition

Answer 5

binds to enzyme substrate complex only, lowers vmax and kmapp, and roundup

Question 6

Noncompetitive Inhibition

Answer 6

inhibitor and substrate can bind simultaneously, doxycycline, inhibitor binds at active site

Question 7

what are the four key types of irreversible inhibitors that can be used to study enzyme function?

Answer 7

group specific inhibitors, suicide inhibitors, affinity analogs, and transition state analogs

Question 8

some bacteria produce enzyme beta-lactamase, which cleaves and opens lactam rings. how would presence of beta-lactamase affect bacterial sensitivity to penicillin?

Answer 8

lactam ring of penicillin reacts with serine residue in glycopeptide transpeptidase, an enzyme that stabilizes bacterial cell wall. if lactam were destroyed, penicillin would be ineffective. presence of beta-lactamase confers penicillin resistance

Question 9

what is the catalytic triad and what are the roles of the individual components in chymotrypsin activity?

Answer 9

catalytic triad composed of serine 195, histidine 57, and aspartate 102 resides at active site of chymotrypsin
histidine residue polarizes hydroxyl group so ready for deprotonation
in presence of substrate, histidine accepts proton from serine hydroxyl group
withdrawal of proton from hydroxyl group generates alkoxide ion which is more powerful nucleophile than hydroxyl.
aspartate helps orient histidine and make it better proton acceptor

Question 10

what is the purpose of the oxyanion hole in chymotrypsin?

Answer 10

it is a structure at the active site of chymotrypsin that stabilizes the tetrahedral intermediate in the proteolysis reaction and facilitates the formation of acyl enzyme intermediate

Question 11

what caused a “burst” of activity followed by steady state reaction when chymotrypsin was studied in milliseconds subsequent to mixing enzyme and substrate?

Answer 11

chymotrypsin cleaves peptide bonds in a 2 step reaction
step 1: formation of acyl enzyme intermediate
step 2: hydrolysis
step 1 is faster

Question 12

if chymotrypsin is such an effective protease, why doesnt it digest itself?

Answer 12

chymotrypsin recognizes large hydrophobic groups, which are usually buried in the enzymes core owing to hydrophobic effects

Question 13

what type of bisubstrate reaction is chymotrypsin?

Answer 13

double displacement (ping pong) catalysis by chymotrypsin involves substituted enzyme intermediate