Enzyme kinetics

Question 1

3 characteristics of enzymes in a reaction

Answer 1

1. Regenerated during course of reaction 2. Do NOT change difference in free energy between reactants and products (_G: Energy of reactants - energy of products) 3. Do NOT change equilibrium of reactants and products

Question 2

4 catalytic mechanisms

Answer 2

1. Transition state stabilization 2. Bond strain 3. Proximity and orientation 4. Covalent catalysis

Question 3

Transition state stabilization

Answer 3

Stability prevents transition state from going back to substrate and increases concentration of intermediate and rate of product formation

Question 4

Catalysis by bond strain

Answer 4

Binding of substrate to enzyme produces bond strain which makes it easier to get to the transition state

Question 5

Covalent catalysis

Answer 5

Covalent intermediate forms between enzyme and substrate due to orientation of active sites on enzymes

Question 6

V0

Answer 6

Initial velocity. V0=_[P]/_t Can only be measured at the very beginning of a reaction when very little product made (<5% [S] converted to [P])

Question 7

Effect of heat and pH on enzymes

Answer 7

Optimal temp and pH ranges where enzymes have the most activity. Outside this range can denature and die

Question 8

Enzyme saturation

Answer 8

Occurs at high [S], hyperbolic curve

Question 9

Steady state

Answer 9

At beginning of reaction [ES] builds up but over time reaches state where [ES] remains constant which will persist until almost all of substrate consumed

Question 10

M-M rate equation 3 assumptions

Answer 10

1. [S]»>[E] so only small amount of S bound to E 2. [ES] is unchanged, stays at steady state 3. Initial velocity (V0) used (so reverse reaction not a factor)

Question 11

M-M equation

Answer 11

v=Vmax_[S]/Km+[S]

Question 12

Km

Answer 12

[S] at _Vmax Constant for a given enzyme. Estimate of the equilibrium constant for S binding to E. Small Km means tight binding and large Km means weak binding

Question 13

Vmax

Answer 13

Theoretical maximum velocity. Constant for a given enzyme. To reach Vmax requires ALL of enzyme molecules to have tightly bound substrate

Question 14

Kcat

Answer 14

Kcat=Vmax/Et (total enzyme) Turnover number. Measure of catalytic activity under saturating substrate conditions. Maximum number of substrate molecules converted to product per enzyme molecule per unit of time. Values range from <1/sec to millions/sec

Question 15

Lineweaver and Burk plot

Answer 15

Used M-M equation to produce a linear plot of catalyzed reactions. Useful for analyzing enzyme inhibition.

Question 16

Competitive enzyme inhibitor

Answer 16

Binds the catalytic site and competes with substrate for binding with dynamic equilibrium-like process. Reversible by substrate.

Question 17

Vmax and Km with competitive inhibitors

Answer 17

Vmax is unchanged (could add a ton of substrate and still get close to Vmax). Km is increased.

Question 18

Vmax and Km with non-competitive inhibitors

Answer 18

Vmax is decreased. Km is unchanged.

Question 19

Non-competitive enzyme inhibitor

Answer 19

Binds E or ES complex at site other than the catalytic site. Substrate binding unaltered but ESI cannot form products. Not reversible by substrate.

Question 20

ACE inhibitors

Answer 20

Angiotensin-converting enzyme inhibitors. Primarily treat HTN and congestive heart failure. Inhibit ACE (component of the blood pressure regulating renin-angiotension system.

Question 21

What causes high blood pressure?

Answer 21

Overactivation of the renin-angiotension-aldosterone system

Question 22

Methotrexate

Answer 22

Anti-metabolite and anti-folate drug. Used in cancer treatment, autoimmune diseases by competitively inhibiting the synthesis of DNA, RNA, thymidylates, and proteins.

Question 23

Aspirin

Answer 23

Supresses production of prostaglandins and thromboxanes due to irreversible inactivation of cyclooxygenase (PTGS) enzyme required for prostaglandin and thromboxane synthesis.

Question 24

Allosteric enzymes

Answer 24

Most are ogliomeric enzymes (consist of multiple subunits). Located near branch points in metabolic pathways, directing substrates along metobolic paths.

Question 25

2 types of effectors for allosteric enzymes

Answer 25

1. Positive and negative heterotropic 2. Substrate itself

Question 26

Heterotropic effectors

Answer 26

Can be positive or negative. Vast diversity of chemical forms and not identical to the substrate.

Question 27

What 2 things can the binding of the Allosteric Regulator alter?

Answer 27

1. Vmax (maximal catalytic activity) 2. Km (affinity for the substrate)

Question 28

Positive feedback

Answer 28

Rate of a process increases as the concentration of the product increases. Goes away from target setpoint.

Question 29

Negative feedback

Answer 29

Controls the rate of a process to avoid accumulation of a product. Goes towards target setpoint.

Question 30

Isoleucine synthesis

Answer 30

Series of reactions starting from threonine regulated by negative feedback

Question 31

Ion channels as enzymes

Answer 31

Catalyze the transmembrane flux of ions. Share features with enzymes including narrow clefts lined with protein loops, specific binding of transition intermediates during catalysis.