Enzymes

Question 1

Enzymes

Answer 1

• large globular proteins
• catalyze chemical reactions in biological systems
• efficient
• specific (one to one)
• unchanged by the reaction
• lower activation energy required to reach transition state

Question 2

Active site

Answer 2

• part of the enzyme, where the substrate binds

- specific AA side chains at the active site

Question 3

what are the 2 models for specificity

Answer 3

lock and key

induced fit - substrate approaches and induces a change in active site so that it fits

Question 4

Coenzymes

Answer 4

• many are derived from vitamins (all water soluble vitamins have some coenzyme role)
• Coenzymes are not specific to one enzyme, they can assist a number of different enzymes even though those enzyme catalyze different reactions
• so one coenzyme can play a role in many rxns!

Question 5

Water Soluble Vitamins:

• *Nicotinic Acid
• *Riboflavin (B2)
• Thiamin (B1)
• Folic Acid/cobalamin (B12)
• Pyridoxine, pyridoxal, pyridoxamine (B6)

Answer 5

= NAD+/NADP+ - hydrogen and electron carriers in oxidation and reduction

=FAD/FMN - hydrogen and electron carriers in oxidation and reduction

=TTP - decarboxylation and acyl transfer

=TH4 - one carbon transfer, rearrangements, methyl-transfers

=CoASH - Transamination, decarboxylation, acyl transfer, carboxylation

Question 6

Cofactors

Answer 6

-metal ion assisting the enzyme in the catalytic process

Question 7

Oxidoreductases

Answer 7

oxidation reduction rxns

Question 8

Transferases

Answer 8

transfer functional groups

-creatine kinase

Question 9

Hydrolases

Answer 9

Hydrolysis rxns

Question 10

Lyases

Answer 10

group elimination to form double bonds

Question 11

Isomerases

Answer 11

Isomerization

Question 12

Ligases

Answer 12

bond formation coupled with ATP hydrolysis

-DNA ligase

Question 13

Define Turnover number

Answer 13

The rate of conversion of substrate to product (when the enzyme is fully saturated)
(amount of substrate that one enzyme can convert to product in a certain time)

Question 14

What are the factors that affect enzyme activity?

Answer 14

PH - bell shapped (denaturation at PH extremes)
Temperature (faster until the protein denatures)
Enzyme concentration (more enzyme = faster rxn)
Substrate concentration (increases rxn rate until approaching vmax)

Question 15

Substrate concentration

Answer 15

At low concentration rxn is first order

Near the maximum concentration the rxn is zero order (constant rate)

Question 16

Km

Answer 16

substrate concentration at half the Vmax

• small Km reflects a HIGH affinity of enzyme for substrate (it doesn’t take a lot of substrate to reach half the max vel)
• large Km reflects a LOW affinity of enzyme for substrate

Question 17

Types of enzyme inhibitors

Answer 17

reversible (competitive)

irreversible (non-competitive)

Question 18

irreversible

Answer 18

-change Vmax!

Organophosphates

• block Ach-esterase
• by covalently binding a serine side chain at active site
• causes paralysis
• examples: Malathion (insecticide); Sarin (chemical weapon)

Aspirin (NSAID)

• inhibits cyclooxygenase (by covalently modifying it)
• without this enzyme can generate the clotting factors
• without clotting factors platelets don’t aggregate
• once platelets die effects of aspirin are lost
• good for acute treatment of gout (allopurinol for long term treatment)

Question 19

reversible

Answer 19

competitive inhibitors don’t affect Vmax
however the Km of the enzyme is usually increased

examples:
sulfamides (first antibacterial agents - inhibit folic acid synthesis in bacteria
methotrexate (cancer therapy - inhibit folate activation)
Warfarin (used as an anti-coagulent)
Statins (inhibit rate limiting step of cholesterol synthesis)
Viagra
ACE inhibitors (cant convert to Ang II) - lower blood pressure - captopril / enalopril
Ibuprofen and Acetaminophen - transient effects like aspirin

Question 20

example questions:

Alcohol can increase level s of uric acid (bc it contains high levels of purine

Other question a competitive inhibitor does what?

Answer 20

• allopurinol was the answer?

- increases the apparent Km

Question 21

sulfonamides

Answer 21

bacterial infections

Dihydropteroate synthetase

Question 22

methotrexate

Answer 22

various neoplasms (especially leukemia)
Dihydrofolate reductase

Question 23

*Allopurinol

Answer 23

gout

Xanthine oxidase

Question 24

Ace inhibitors (captopril, enalopril)

Answer 24

high blood pressure

Angiotensin converting enzyme

Question 25

Warfarin (coumadin, dicumarol)

Answer 25

Thrombosis

glutamate carboxylase

Question 26

Statins (lovastatin, simvastatin, mevastatin)

Answer 26

Elevated plasma cholesterol

HMG-CoA reductase

Question 27

Aspirin

Answer 27

Inflammation, pain, CAD

cyclo-oxygenase

Question 28

enzyme diagnosis

Answer 28

enzymes level paint an up to date picture because if treated enzyme levels return to normal

Question 29

Myocardial Infarction

Answer 29

AST (aspartate aminotransferase)
CK (creatine kinase)
LDH (lactate dehydrogenase)

Question 30

*Obstructive Liver Disease (alcoholics)

Answer 30

GGT (glutamyl transferase)

Question 31

Acute pancreatitis

Answer 31

*Lipase

amylase (also for mumps)

Question 32

Prostate CANCER, bone disease

Answer 32

alkaline phosphatase

Question 33

hepatitis (alcoholics)

Answer 33

AST > ALT

Question 34

hepatitis (viral)

Answer 34

ALT > AST

Question 35

Duchenne muscular dystrophy

Answer 35

CK