Enzymes

Question 1

Biochemists are interested in enzyme kinetics because…

Answer 1

• elucidation of catalytic mechanisms
• understanding the roles of enzymes
  within metabolic processes.
• optimization of enzyme-catalyzed
  processes (PCR, chemical synthesis,
  ethanol production, etc).

Question 2

Kinetics is concerned with…

Answer 2

the rates of chemical
reaction.

– Enzyme kinetics addresses the biological roles of
enzymatic catalysts and quantifies the remarkable
functions of biological enzymes

Question 3

Enzyme kinetics information can be exploited…

Answer 3

– to control and manipulate the course of metabolic events

• Pharmaceuticals or drugs are often special inhibitors targeted at a particular enzyme.

– the science of pharmacology relies on such information

Question 4

Enzymes:

Answer 4

• Living organisms must be able to carry out
  chemical reactions which are
  thermodynamically very unfavorable.

– Break and form covalent bonds

– Move large structures

– Effect three dimensional structure

– Regulate gene expression

• They do so through enzyme catalysis

Question 5

Enzymes can have massive effects:

Answer 5

• Most common biological reactions can take
  place without enzyme catalysis

– Can take 750,000,000 years

• Versus: With enzyme 22 milliseconds
• A bag of sugar can be stored for years with
  very little conversion to CO2
  and H2O

– Yet this conversion is basic to life

– When sucrose is consumed by cells, it is
converted to chemical energy very fast

Question 6

Catalysis carried out by…

Answer 6

very highly specialized class of proteins: Enzymes

– Specialized to perform specific chemical
reactions

– Specialized to work in specific environments

Question 7

Enzymes have immense importance in…

Answer 7

a number of
fields.

– Genetic diseases are frequently defects in enzymes or increased/decreased levels of enzymes

• Important diagnostic tools

– Drugs exert effects by interacting with enzymes

• MAO inhibitors

– Used in food processing and in chemical industry

– Enzyme inhibitors are a foundation of biological
weapons

Question 8

Hydrolysis of ATP is…

Answer 8

thermodynamically favorable but ATP is kinetically stable

Question 9

Transition state =

Answer 9

intermediate chemical state Required for reactants to form products = higher energy than reactants

Question 10

Activation energy (EA
) =

Answer 10

minimum energy required to form transition state

Question 11

Number of molecules possessing energy > EA =

Answer 11

numbers of molecules able to form product

Question 12

Number of molecules possessing energy > EA =

Answer 12

numbers of molecules able to form product

Question 13

Life depends upon the…

Answer 13

high activation
energies that prevent most cellular
reactions occurring at appreciable rates
without a catalyst.

-Allows reactions to
be regulated.

Question 14

Enzymes accelerate reactions by…

Answer 14

decreasing G‡.

• Catalysts get the reaction to the equilibrium faster, but don’t affect Keq

Question 15

Biological catalysts / Enzymes do NOT…

Answer 15

change direction of reaction

• DO increase the rate of reaction by
  lowering EA
• Form transient complex with substrate(substrate = substance upon which an enzyme acts)

Question 16

Catalysis occurs at the…

Answer 16

active site.

Question 17

Active site:

Answer 17

• Substrate binds to enzyme at active site
• Usually groove or pocket
• Substrate fits with high specificity
• Usually only 5% of protein
• Amino acids in active site often not contiguous

Question 18

Enzymes are sophisticated
catalysts (4)

Answer 18

• Active Site
  – Is complementary in shape
  and functionality with the
  substrate.
• Catalytic Efficiency
  – Rate increased 103
  -108
• Specificity
  – Reactions are extremely
  specific in both the substrates
  and the products.
• Regulation

Question 19

Kinetics Is the science that describes…

Answer 19

the properties of a chemical reaction including those mediated by enzymes (catalysis)

Question 20

Kinetics measures…

Answer 20

the concentration of substrate
and/or products of a reaction to determine the velocity of the reaction

• Measures the effects of concentration,
  temperature, pH, etc. to characterize the
  properties of the enzyme catalyzing the
  reaction

Question 21

Enzyme Kinetics Is…

Answer 21

• An approach to understanding the mechanism of action of enzymes
• An approach to understanding how mutations may effect function
• An approach to understanding how changes in the
  physical and chemical environments change function

Question 22

Enzymes Do…

Answer 22

1. Lower energy of activation of forward
   and reverse reactions
2. Reduce the time required to reach equilibrium
3. Stabilize the Transition State
4. Conduct a specific reaction with no side products

Question 23

Enzymes Don’t…

Answer 23

1. Change the ΔG of a Reaction
2. Change the Equilibrium Position of a Reaction
3. Change the Energy Yield
   (or requirement) of a Reaction

Question 24

Enzyme Definition:

Answer 24

A protein (or RNA) molecule that has the property of a catalyst, sometimes called a
biocatalyst.

Question 25

Substrate Defnition:

Answer 25

The target of the enzyme’s action. The molecule that will undergo chemical change as a result of the enzyme.

Question 26

Enzyme activity definition:

Answer 26

A measure of the enzyme’s
catalytic effectiveness as manifested by the rate of the reaction catalyzed.

Question 27

Cofactor Definition:

Answer 27

A component that works with the enzyme in effecting catalysis. Any chemical factors that assist the activity of an enzyme-catalyzed reaction.

Question 28

Coenzyme Definition:

Answer 28

Related to cofactor, but generally used to describe molecules that are derived from B-vitamins.

Question 29

Enzyme kinetics Definition:

Answer 29

A branch of enzymology that deals with mechanism as studied by factors that affect the
rate of enzyme reactions.

Question 30

Active Site Definition:

Answer 30

That region on the enzyme surface or
within a crevice where the substrate binds and
catalysis is performed.