Enzymology

Question 1

What are enzymes

Answer 1

a molecular catalyst in a biological system. Most but not all are proteins

Question 2

Properties of enzymes:

Answer 2

1. Have immense catalytic power
2. Highly specific
3. Usually catalyze only single chemical reaction or a set of closely related chemical reactions.

Question 3

Components of a protein enzyme:

Answer 3

1. 1 or more polypeptide chains.
2. Cofactor: an additional non peptide component of an enzyme
3. Coenzyme: a complex organic or metalloorganic cofactor
4. Prosthetic group: covalently bound cofactor
5. Holoenzyme: a complete, catalytically active enzyme
6. Apoenzyme: protein portion of holoenzyme.

Question 4

Many vitamins are precursors of

Answer 4

coenzymes

Question 5

What is the transition state

Answer 5

the configuration (of atoms, bonds, electrons) along the reaction coordinate corresponding to the highest energy

Question 6

At the transition state, there is an ____probability of forming reactants or products

Answer 6

equal

Question 7

Change in free energy from reactants to transition state is called the

Answer 7

activation energy

Question 8

Rate constant of a reaction (k) is ____ and ___ proportional to the activation energy

Answer 8

inversely and exponentially

Question 9

Activation energy determines the rate of a reaction at a given:

Answer 9

temperature

Question 10

The higher the AE =

Answer 10

slower rate

Question 11

The lower the AE=

Answer 11

faster rate

Question 12

Enzymes ____activation energy

Answer 12

lower

Question 13

What is the active site of an enzyme

Answer 13

the location on enzyme where substrate(s) bind. Provides specific environment for reactions

Question 14

Active site features:

Answer 14

1. 10 or fewer aa
2. water usually excluded from site
3. Non polar envmt, so aa side chains become highly active

Question 15

How is activation energy reduced

Answer 15

Loaned energy from weak, non covalent interactions between the substrate and active site. Each interaction releases a small amount of energy that can be offset against activation energy. The sum of these energies released by substrate active site interaction is called the binding energy

Question 16

Activation energy -binding energy =

Answer 16

catalyzed activation energy

Question 17

What is the lock and key hypothesis

Answer 17

Proposed that shape of substrate and active site must match in order for substrate to fit side

Question 18

T/F There is a problem if weak interactions between enzymes and substrates are optimized in the enzyme substrate complex

Answer 18

T

Question 19

What is the induced fit hypothesis

Answer 19

Once substrate bound, structure of enzyme shifts so active site assumes closer fit

Question 20

Weak interactions between enzyme and substrate are optimized in the

Answer 20

transition state

Question 21

poorer fit –> lower binding energy–> higher activation energy–> ____reaction rate

Answer 21

slower

Question 22

Thrombin is a proteolytic enzyme and only cleaves between ____ and ____

Answer 22

argenine and glycine

Question 23

What is catalysis

Answer 23

The active site can provide functional groups that interact transiently with the substrates

Question 24

3 common types of catalysis involving functional groups are

Answer 24

1. acid base
2. covalent
3. metal ion

Question 25

Positively charged intermediates:

Answer 25

remove proton (base)

Question 26

Negatively charged intermediates:

Answer 26

add proton (acid)

Question 27

Specific acid/base catalysis:

Answer 27

acid or base from water

Question 28

General acid/base catalysis:

Answer 28

proton donor/acceptor

Question 29

What is covalent catalysis

Answer 29

A transient covalent link is formed between the enzyme and substrate or intermediate

Question 30

What is metal ion catalysis

Answer 30

Metal ions can be tightly bound to enzyme or taken up with substrate. Ionic interactions between metal ion and substrate help orient substrate and/or stabilize charged transition state.