Lecture 3 -Enzymes

Question 1

Oxioreductases

Answer 1

Oxidation-reduction reactions

Question 2

Transferases

Answer 2

Transfer of C, N, or P containing groups

Question 3

Hydrolases

Answer 3

Cleavage of bonds by addition of water

Question 4

Isomerases

Answer 4

Racemization of optical or geometric isomers

Question 5

Ligases

Answer 5

Formation of bonds between carbon and O, S, N coupled to hydrolysis of high energy phosphates

Question 6

Lyases

Answer 6

Cleavage of C-C, C-O, and C-S and certain C-N bonds

Question 7

Isoenzymes

Answer 7

Different enzymes that catalyze same reaction, usually in different tissues
-hexokinase/glucokinase -lactate dehydrogenase -creatine kinase

Question 8

Proenzyme/Zymogen

Answer 8

Inactive enzymes w extra protein sequence activated by cleavage of of protein synthesis
-Digestive proteases -Blood coagulation enzymes

Question 9

Apoenzyme

Answer 9

Inactive form of enzyme

Question 10

Holoenzyme

Answer 10

Active form, enzyme + cofactor

Question 11

Cofactor Types

Answer 11

Metal ions: -Bind substrate or participate in oxidation-reduction
-Small orgnic molecules (coenzyme): -Transfer of chemical groups or oxidation-reduction (usually enzymes)

Question 12

Vmax

Answer 12

• Theoretical maximum velocity
• Directionally proportional w enzyme concentration
• 1/Vmax is Y intercept on linearized Michaelis-Menten equation (small y-intercept = large Vmax)

Question 13

Km

Answer 13

• Substrate concentration that permits reaction velocity of Vmax/2
• Inversely related to affinity of enzyme for substrate (high Km=low affinity, low Km = high affinity
• 1/Km is X-intercept on linearized plot (small x intecept = large Km = low affinity)

Question 14

Product Inhibition

Answer 14

Product of enzymatic reaction is an inhibitor of the enzyme, regulates own synthesis
-Heme

Question 15

Allosteric Regulation

Answer 15

Regulators bind outside of active site and cause conformational change that alter enzyme activity positively or negatively
-Can change Vmax or Km

Question 16

Homotropic Effector

Answer 16

• Substrate itself is allosteric effector in multisubunit enzyme
• Binding of substrate to one subunit changes binding of substrate to other units (ex. Binding of O2 to hemoglobin increases affinity)
• Changes shape of curve

Question 17

Heterotropic Effector

Answer 17

• Allosteric effector is different from substrate
• Doesnt compete for active site (Ex. 2,3-BPG decreases O2 affinity, but doesnt bind active site)
• Changes Km

Question 18

Phospohorylation/dephosphorylation

Answer 18

Kinases/phosphotases add/remove phosphate groups to enzymes -Changes enzymatic activity depending on enzyme
-Ex. Gycogen synthase phosphorylated is inhibited, glycogen phosphorylase phosphorylated is activated

Question 19

Proteolytic Processing

Answer 19

-Enzymes are produced in proenzyme (inactive) form -Cleavage of proenzyme leaves active form

Question 20

Regulation of Enzyme Levels

Answer 20

• Transcription, translation, degredation of enzyme are regulated
• Heme

Question 21

Negative Feedback Inhibition

Answer 21

End product of pathway regulates first step in pathway

Question 22

Reversible Enzyme Inhibitors

Answer 22

Bind non-covalently to enzyme, so can be dissociated from enzyme

• Competitive
• Noncompetetive

Question 23

Competetive

Answer 23

Inhibitor competes with the substrate at the active site

Drugs: -Statins -Ibuprofen -Catopril

Question 24

Non Competetive

Answer 24

Inhibitor does NOT compete w enzyme at active site

Question 25

Irreversible Enzyme Inhibitors

Answer 25

Bind very tightly (usually covalently) to active site and prevent substrate binding - Transition-state (Active site-directed) - Suicide Inhibitors (Enzyme-activated)

Question 26

Transition-state (Active site-directed)

Answer 26

Inhibitor (without alteration in its structure) forms covalent linkage w catalytic site Drugs: -Organophosphates -Aspirin

Question 27

Suicide Inhibitors (Enzyme-activated)

Answer 27

Enzyme modifies inhibitor, inhibitor binds very tightly to active site and cant be displaced Drugs: -Penicillin -Allopurinol

Question 28

AST

Answer 28

-Aspartate Aminotransferase -Aspartate -> glutamate Tissue: heart, skeletal muscle, liver, brain Diagnostic Use: liver disease

Question 29

ALT

Answer 29

-Alanine Aminotransferase -Alanine -> glutamate Tissue:Liver Diagnostic Use: Liver disease (ALT> AST)

Question 30

Amylase

Answer 30

Tissue: Pancreas, Salivary gland | Diagnostic Use: Acute pancreatitis, biliary obstruction

Question 31

CK

Answer 31

-Creatine Kinase Tissue: Skeletal muscle, heart, brain Diagnostic Use: Muscular dystrophy, MI

Question 32

GGT

Answer 32

Tissue: Liver | Diagnostic Use: hepatitis, cirrhosis

Question 33

LDH

Answer 33

Tissue: Heart, liver erythrocytes | Diagnostic Use: Lymphoma, hepatitis

Question 34

Lipase

Answer 34

Tissue: Pancreas | Diagnostic Use: Acute pancreatitis, biliary obstruction

Question 35

Alkaline Phosphatase

Answer 35

Tissue: Osteoblast | Diagnostic Use: bone disease/tumors

Question 36

Acid Phosphatase

Answer 36

Tissue: Prostate | Diagnostic Use: Prostate cancer