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Biochemistry I > Enzymes > Flashcards

Flashcards in Enzymes Deck (35)
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1

Most enzymes are...

Globular proteins

2

Examples of enzyme cofactors

Inorganic (Mg+, Zn+), organic (called coenzymes), prosthetic groups, apoenzymes.

3

Types of coenzymes

Coenzyme A and NAD+.

4

Coenzyme bound to enzyme protein =

Prosthetic group.

5

Apoenzyme

Without coenzyme

6

Holoenzyme

With coenzyme.

7

How does an apoenzyme become active

By binding of coenzyme or cofactor to enzyme. Holoenzyme is formed when it binds to the active site.

8

Oxidoreductases

Catalyze the transfer of electrions.

9

Transferases

Catalyze group transfer reactions.

10

Hydrolases

Catalyze hydrolysis reactions.

11

Lyases

Catalyse cleavage of C-C, C-O, and C-N or other bonds by elimination. Leave behind double bonds or rings.

12

Isomerases

Catalyze the transfer of groups within molecules to yield isomeric forms.

13

Ligases

Catalyze the formation of C-C, C-S, C-O and C-N bonds by condensation reaction coupled to cleavage of ATP or similar cofactor.

14

Enzymes do not...

Affect equilibrium, cannot change free energy.

15

Enzymes do affect...

Rates of reaction, decrease activation energy.

16

How do enzymes lower activation energy?

They organize reactive groups into close proximity and proper orientation (into a fairly rigid ES complex) by using enzyme substrate binding energy.

17

Enzyme active sites are complimentary too...

The transition state of the reaction.

18

Enzyme substrate binding results in...

Reduction of entropy, hindering the reaction.

19

Acid-base catalysis

Give and take protons

20

Covalent catlysis

Change reaction paths. Requires a nucleophile on the enzyme

21

Metal ion catalysis

Use redox cofactors, pKa shifters. Stabilizes negative charges.

22

In steady state conditions...

ES formed = ES consumed

23

ES association and dissociation depend on...

Constants (K) which reflect E and E properties.

24

Reaction rate is proportional to...

ES complex.

25

Kcat

Turnover rate, number of S molecules converted to P per time. Unit is 1/s .

26

Kcat and Km reflect the...

Cellular environment.

27

Enzyme efficieny

The specificity constant, Kcat/Km.

28

Enzyme efficient is limited by...

Specificity.

29

Kinetic mechanism

The order of binding of substrates and release products

30

Competitive inhibition

Competes with substrate for binding, binds to active site, does not affect catalysis. No change in Vmax, apparent increase in Km.