enzymes 1

Question 1

describe the unusual temperature dependence of enzymes

Answer 1

initially, increasing temp will increase rate (2x per 10*C) until temp is too high and enzyme begins to denature, then enzyme activity will decrease

Question 2

discuss the significance of G6P dehydrogenase mutation

Answer 2

enzyme is impt in RBC membrane, d/t the mutation of G6PD, less NADPH is formed and bc less NADPH is formed, there is less to participate in the reduction of glutathione, leading to less GSH. when GSH levels are low, peroxides and free radicals accumulate, leading to cell damage

Question 3

which aa form covalent intermediates? (4)

Answer 3

cysteine
lysine
serine
histidine

Question 4

which aa participate in acid-base catalysis? (2)

Answer 4

histidine

aspartate

Question 5

which aa stabilize anions? (3)

Answer 5

peptide backbone-NH
arginine-NH
serine-OH

Question 6

which aa stabilize cations? (1)

Answer 6

aspartate- COO-

Question 7

function of lyases

Answer 7

add/remove groups to form double bonds

Question 8

vitamin B1

Answer 8

thyamine pyrophosphate
-aldehyde transfer
- beri-beri if deficient
used by pyruvate dehydrogenase

Question 9

vitamin B2

Answer 9

riboflavin (FAD)

• Redox
• chellosis, dermatitis

Question 10

vitamin B6

Answer 10

pyridoxal phosphate
- group transfer to and from aa
- depression, confusion if deficient
used in liver to keep toxic NH2 from accumulating in the blood

Question 11

nicotinic acid

Answer 11

NAD

• Redox
• pellagra (dermatitis, depression, diarrhea) if deficient

Question 12

biotin

Answer 12

activates and transfers CO2

Question 13

coenzyme A

Answer 13

used to transfer acyl groups or thiol esters

Question 14

cofactor used by alcohol dehydrogenase

Answer 14

NAD

Question 15

in the active site of alcohol dehydrogenase (3)

Answer 15

Zn, serine and histidine

Question 16

stereospecificity of alcohol dehydrogenase

Answer 16

enzyme is steroespecific in that H and D forms are not equal

Question 17

catalysis and motion

Answer 17

enzymes help to catalyze run by restricting motion, the more restricted the motion, the faster the rate of rxn

Question 18

4 aa found in the active site of all of the serine proteases

Answer 18

serine
histidine
glycine
asparagine

Question 19

which other enzyme has identical catalytic site to serine proteases?

Answer 19

acetylcholinesterase

Question 20

MOA of chymotrypsin (9)

Answer 20

• substrate binds to substrate-specificity site
• His activates Ser for nucleophilic attack
• Ser attacks at carbonyl carbon and oxyanion tetrahedral intermediate is formed between Ser, Gly and substrate
• peptide bond is cleaved, amino portion released
• covalent act-intermediate between Ser and substrate
• hydrolysis
• formation of second oxyanion intermediate
• acid-base catalysis with histidine breaks acyl-enzyme bond
• product dissociates

Question 21

different binding sites for the serine proteases (3)

Answer 21

chymotrypsin- open for large, hydrophobic substrates
trypsin- has aspartate in site (-), so attracts (+) substrate
elastin- has valine and threonine blocking binding site, only allows small substrates like glycine

Question 22

enzyme that activates trypsinogen –> trypsin

Answer 22

enteropeptidase

Question 23

3 enzymes activated by trypsin

Answer 23

proelastase –> elastase
procarboxypeptidase –> carboxypeptidase
chymotrypsin –> p-chymotrypsin

Question 24

what causes the formation of a-chymotrypsin?

Answer 24

p-chymotrypsin (both forms are active)