Biochem - Enzymes

Question 1

6 major classes of enzymes:

Answer 1

• Ligases
• Lyases
• Hydrolyases
• Isomerases
• Oxidoreductase
• Transferases

Question 2

What 4 things affect enzyme reactions?

Answer 2

• enzyme
• substrate
• effectors
• temperature

Question 3

Do enzymes get used up?

Answer 3

No; they are catalysts

Question 4

4 reasons biocatalysts are preferred over inorganic catalysts:

Answer 4

• greater reaction specificity: avoid side products
• higher reaction rates: biologically useful timeframes
• milder reaction conditions: conducive to cell conditions
• capacity for regulation: control biological pathways

Question 5

What 2 reaction conditions are compatible with life?

Answer 5

• 37 degrees C
• pH of 7

Question 6

Ligases (synthetases)

Answer 6

• join 2 molecules at the expense of ATP
• require energy

Question 7

Lyases

Answer 7

remove atoms to form double bonds or add atoms to double bonds

Question 8

Hydrolyases

Answer 8

cleave bonds with addition of water

Question 9

Isomerases

Answer 9

• move functional groups within a molecule
• only one substrate and one product
• think racemic mixtures or epimers

Question 10

Oxidoreductases (dehydrogenases)

Answer 10

catalyze oxidation-reduction reactions

Question 11

Transferases (kinases)

Answer 11

• move functional groups between molecules
• induces kinases

Question 12

Exergonic

Answer 12

• neg (-) delta G
• spontaneous
• favorable

Question 13

Endergonic

Answer 13

• pos (+) delta G
• non spontaneous
• nonfavorable
• must be coupled to exergonics in order to form a net delta G that is favorable

Question 14

H:

Answer 14

• amount of heat absorbed or released
• aka exothermic or endothermic

Question 15

Exothermic

Answer 15

releases heat -> -

Question 16

Endothermic

Answer 16

absorbs heat -> +

Question 17

S:

Answer 17

• entropy
• state of disorder and randomness

Question 18

What info does delta G provide?

Answer 18

• only spontaneity
• NOT reaction rate

Question 19

Do enzymes alter delta G?

Answer 19

No

Question 20

Do catalysts alter reaction equilibria?

Answer 20

No

Question 21

What do enzymes affect?

Answer 21

they decrease the free activation energy (delta G) of a reaction

Question 22

Which model goes through a conformational change? (Lock-and-key OR Induced-fit)

Answer 22

Induced-fit

Question 23

What kinase is in all tissues?

Answer 23

hexokinase

Question 23

Which model does hexokinase go through?(Lock-and-key OR Induced-fit)

Answer 23

Induced-fit

Question 24

What kinase is in liver cells?

Answer 24

glucokinase

Question 25

Michaelis-Menten equation

Answer 25

Question 26

Km is the substrate concentration that yields what?

Answer 26

1/2 Vmax

Question 27

Kcat:

Answer 27

how many substrate molecules can one enzyme molecule convert per second

Question 28

Km:

Answer 28

measure of a substrates affinity for an enzymes

Question 29

Kcat / Km

Answer 29

measure of catalytic efficiency

Question 30

2 types of kinetic mechanisms

Answer 30

• sequential (random and ordered): requires ternary complex
• ping-pong: no ternary complex is required

Question 31

sequential mechanism graph

Answer 31

lines intersect

Question 32

ping pong mechanism graph

Answer 32

lines are parallel

Question 33

What type of inhibitor is used in drugs?

Answer 33

reversible inhibitor

Question 34

What type of in inhibitor is a powerful toxin

Answer 34

irreversible inhibitor

Question 35

competitive inhibition

Answer 35

• competes with substrate for binding; binds active site
• no change in Vmax; decrease in Km
• lines intersect at y axis

Question 36

uncompetitive inhibition

Answer 36

• only binds to ES complex (does not affect substrate)
• decrease in Vmax; decrease in Km
• lines are parallel

Question 37

mixed inhibition

Answer 37

• binds enzyme w or wo substrate
• decrease in Vmax; change in Km
• lines intersect LEFT of y axis
• Non-comepetitive inhibitors are mixed inhibitors (no change in Km)

Question 38

Competitive, noncompetitive, and uncompetitive plots

Answer 38