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Flashcards in Enzymology Deck (30):
1

What are enzymes

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

2

Properties of enzymes:

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

3

Components of a protein enzyme:

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.

4

Many vitamins are precursors of

coenzymes

5

What is the transition state

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

6

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

equal

7

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

activation energy

8

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

inversely and exponentially

9

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

temperature

10

The higher the AE =

slower rate

11

The lower the AE=

faster rate

12

Enzymes ____activation energy

lower

13

What is the active site of an enzyme

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

14

Active site features:

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

15

How is activation energy reduced

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

16

Activation energy -binding energy =

catalyzed activation energy

17

What is the lock and key hypothesis

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

18

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

T

19

What is the induced fit hypothesis

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

20

Weak interactions between enzyme and substrate are optimized in the

transition state

21

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

slower

22

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

argenine and glycine

23

What is catalysis

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

24

3 common types of catalysis involving functional groups are

1. acid base
2. covalent
3. metal ion

25

Positively charged intermediates:

remove proton (base)

26

Negatively charged intermediates:

add proton (acid)

27

Specific acid/base catalysis:

acid or base from water

28

General acid/base catalysis:

proton donor/acceptor

29

What is covalent catalysis

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

30

What is metal ion catalysis

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.