Enzymes

Question 1

how do enzymes catalyze reactions?

Answer 1

• increase chemical reaction rate
• reduce the free energy needed to drive a chemical reaction
• increase the probability of reaction occurence

Question 2

describe simple enzymatic reactions

Answer 2

• enzyme reacts with a substrate
• enzyme reacts with a product
• can be bidirectional or unidirectional

Question 3

vast majority of enzymes are?

Answer 3

large globular proteins, with the exception of catalytic RNAs

Question 4

are substrates and binding pockets selective?

Answer 4

• yes

- once bound, conformational change occurs

Question 5

what do coenzymes do?

Answer 5

bind to protein to allow binding of substrate

Question 6

what are cofactors?

Answer 6

inorganic ions that bind to enzymes to allow binding of substrate

Question 7

what is a holoenzyme?

Answer 7

• a catalytically active enzyme with coenzymes and cofactors bound
• classified by reaction type

Question 8

what do oxidoreductases do?

Answer 8

-transfer of electrons

Question 9

what do transferases do?

Answer 9

group transfer reactions

Question 10

what do hydrolases do?

Answer 10

hydrolysis reactions

Question 11

what do lyases do?

Answer 11

cleavage of C-C, C-O, C-N, or other bonds

Question 12

what do isomerases do?

Answer 12

transfer of groups within molecules to yield isomeric forms

Question 13

what do ligases do?

Answer 13

formation of C-C, C-S, C-O, and C-N bonds by condensation reactions

Question 14

How do enzymes enhance reaction rates?

Answer 14

-reduce activation energies by lowering free energy thresholds

Question 15

T or F:

enzymes covalently change chemical structure

Answer 15

true

Question 16

T or F:

substrate complementation would decrease free energy demands

Answer 16

false

increase

Question 17

T or F:

enzymes shift substrates into the transition state

Answer 17

true

Question 18

T or F:

strong bonding is optimal in the transition state

Answer 18

false

weak binding

Question 19

T or F:

strong bonding releases free energy

Answer 19

false

weak bonding

Question 20

T or F:

weak bonding drives enzyme catalysis

Answer 20

true

Question 21

Name the 4 activation barriers that enzymes overcome

Answer 21

• entropy of molecules in a solution
• solvation shell
• substrate conformation
• substrate orientations

Question 22

Name the 4 binding energies needed for enzymes to overcome the 4 activation barriers

Answer 22

• organize substrates, reduce entropy to overcome entropy of molecules in a solution
• weak bonds desolvate substrates to overcome solvation shell
• weak bonds alter conformation to overcome substrate conformation
• enzymes induce fit to overcome substrate orientations

Question 23

what do enzyme kinetics do?

Answer 23

-they regulate the rate at which enzymes create products

Question 24

what do kinetic studies allow?

Answer 24

• identification of mechanism
• rate limiting steps of product formation
• identification of inhibitors
• this all measures the velocity

Question 25

what is velocity?

Answer 25

• the primary measure of reaction rate
• initial velocity (rate within first few second of reaction) and maximum velocity (max speed at which reaction can occur)

Question 26

what is velocity affected by?

Answer 26

• [enzyme]
• [substrate]
• cofactors and coenzymes
• enzyme modifications
• pH
• temperature

Question 27

what is the Michaelis-Mentin constant?

Answer 27

-the substrate concentration needed for initial velocity to reach 1/2 of the maximum velocity

Question 28

what are the 4 assumptions in Michaelis-Mentin kinetics?

Answer 28

1) single substrate enzyme reaction
2) free diffusion of substrate
3) substrate concentration is below Vmax
4) constant conditions

Question 29

what do allosteric enzymes do?

Answer 29

• increase or decrease enzyme efficiency by binding and changing conformation
• do not follow Michaelis-Menten kinetics
• consequence of globular proteins having complex structures

Question 30

in what ways are allosteric enzymes post-translationally modified?

Answer 30

• phosphorylation
• methylation
• myristoylation
• acetylation
• ubiquitination

Question 31

in what way do allosteric enzymes not follow michaelis-menten kinetics?

Answer 31

• homotropic and heterotropic regulation

- regulation occurs at a separate site from substrate binding

Question 32

what is the difference between homotropic regulation and heterotropic regulation

Answer 32

• homotropic regulation - substrate regulates enzyme function
• heterotropic regulation - non-substrate molecule regulates enzyme function

Question 33

what 2 major processes do enzymes drive?

Answer 33

metabolism and signal transduction

Question 34

name 7 characteristics of enzymes

Answer 34

1) most commonly globular proteins, with the exception of catalytic RNAs
2) substrate selective
3) can have coenzymes
4) weak interactions
5) cofactors
6) classified by reaction type
7) can become holoenzymes