Chapter 13 & 14- Enzyme Specificity and Kinetics

Question 1

Enzymes are _____ that increase _______ but are not _______

Answer 1

catalysts, reaction rate, consumed

Question 2

Most enzymes are _____, except ____- which are catalytic RNA

Answer 2

proteins, ribozymes

Question 3

What is the active site?

Answer 3

the pocket on the enzyme where the reaction takes place

Question 4

Substrate definition

Answer 4

molecule bound in the active site and acted upon

Question 5

How are enzymes different from ordinary chemical catalysts?

Answer 5

• Higher Reaction Rates
• Operate under mild reaction conditions
• Greater reaction specificity
• Capacity for Control

Question 6

Enzyme-catalyzed reaction rates are _______ than with chemical catalysts

Answer 6

several orders of magnitude higher

Question 7

Enzymes are named by adding the suffix ____

Answer 7

-ase

Question 8

Enzymes are named for their _____

Answer 8

broad function

Question 9

A substrate binds _____ to an enzyme at a specific site

Answer 9

non-covalently

Question 10

Driving force of substrate binding

Answer 10

water release

Question 11

Interactions and forces involved with substrate binding?

Answer 11

• Van der Waals
• Electrostatic interactions
• H-bonding
• Hydrophobic interactions

Question 12

What is geometric complementarity

Answer 12

the substrate is complementary in shape to the active site

Question 13

what is electronic complementarity

Answer 13

binding site attracts the substrate

Question 14

Substrate specificity: of serine proteases

Answer 14

catalyze hydrolysis of amide bonds via a serine

Question 15

Substrate specificity of Chymotrypsin

Answer 15

specific for a bulky hydrophobic residue

Question 16

substrate specificity of trypsin

Answer 16

specific for a positively charged residue

Question 17

substrate specificity of elastase

Answer 17

specific for a small neutral residue

Question 18

Enzymes vary in their degree of _____

Answer 18

geometric specificity

Question 19

characteristics of Geometric specificity of enzymes

Answer 19

• some are very specific
• some have more relaxed specificity

Question 20

Enzymes bind ______ substrates

Answer 20

chiral

Question 21

Enzymes catalyze reactions in a _____

Answer 21

stereospecific manner

Question 22

Enzymes and ligands exhibit some degree of ______ fit

Answer 22

induced

Question 23

What does induced fit mean

Answer 23

Enzymes change shape around the substrate when they bind and the substrate adapts to the protein

Question 24

Enzymes must be complementary to the ________ state

Answer 24

reaction transition

Question 25

Thermodynamics predict _____, it does not say anything about the _____

Answer 25

whether a reaction is spontaneous rate of the reaction

Question 26

Enzymes kinetics are important for:

Answer 26

- Elucidation of catalytic mechanism - Role of a specific enzyme in a metabolic process - Determine binding affinities of substrates or inhibitors to enzymes - determine how much enzyme is present

Question 27

How can the rate of a unimolecular reaction be determined?

Answer 27

measuring [A] or [P] as a function of time

Question 28

For the reaction to occur, the existence of a high energy (unstable) complex is needed which is an _____

Answer 28

activated complex

Question 29

The gibbs free energy of activation is also called the _____

Answer 29

activation barrier

Question 30

Ways to increase the reaction rate

Answer 30

1. raising the temp 2. lowering gibbs free energy

Question 31

Catalysts act by _____

Answer 31

lowering the activation barrier

Question 32

The kinetic barrier is lowered by the _______ for both the forward and the reverse reactions

Answer 32

same amount

Question 33

The equillibrium constant for the reaction _____ when catalyzed

Answer 33

remains the same

Question 34

The slowest step in the reaction has the _____

Answer 34

highest activation barrier

Question 35

If K1< K2 then ____

Answer 35

1st step is the slowest

Question 36

If K1>K2 then ____

Answer 36

2nd step is the slowest

Question 37

The slow step acts as a _____ which is the ______ of the reaction

Answer 37

bottleneck, rate-determining step

Question 38

Assumption of steady state

Answer 38

substrate is in great excess over enzyme

Question 39

[ES] remains ~ _______ until the substrate is nearly exhausted

Answer 39

constant

Question 40

The rate of synthesis of ES must _____ its rate of consumption

Answer 40

equal

Question 41

[ES] maintains a steady stade which means the change in [ES]=? not that [ES]=?

Answer 41

0

Question 42

Vmax occurs when [S] is very ___

Answer 42

high

Question 43

Steps to determine V0

Answer 43

1. measure appearance of the product 2. plot signal vs. time 3. repeat for different [S] ([E] is the same for each experiment) 4. determine d[S]/t or d[P]/t.

Question 44

Km is the substrate concentration at which the reaction velocity is ______

Answer 44

half maximal

Question 45

Km is a measure of the _____ of the enzyme for the substrate

Answer 45

affinity

Question 46

If one step is the rate limiting step, then Kcat is ____ to the rate constant for the limiting step

Answer 46

equivalent

Question 47

A higher value of the specificity constant means ____

Answer 47

a higher catalytic effeceincy

Question 48

two enzymes may have the same Kcat but the rate of the uncatalyzed reactions may be ____

Answer 48

different

Question 49

Virtual catalytic perfection def

Answer 49

Enzyme with Kcat/Km in thsi range must catalyze the reaction every time it encounters the substrate