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Flashcards in Enzyme Catalysis Deck (44):
1

Enzymes are biological catalysts. Describe what a catalyst does

increases rate of reaction but does not effect the equilibrium constant

2

A catalyst decreases activation energy. True or false?

true

3

Does an enzyme effect the free energy of a reaction?

no

4

Reaction rates of enzymatically catalyzed reactions are generally how much greater than non-catalyzed reactions? non-enzymatically catalyzed reactions?

10^6 - 10^12; 10^3

5

Enzymatic reactions have milder reaction conditions. Describe some of these conditions

occur at atmospheric pressure, neutral pH, and temperatures less than 100 degrees celsius

6

Enzymatic reactions have tremendous reaction specificity that results in what?

very rarely occurring side products

7

True or false?
Enzyme activity can vary in response to biological molecules other than the enzyme's substrates or products

true

8

What is a unit of enzyme activity?

the amount of substrate converted to product in a given amount of time

9

What is a specific activity of an enzyme?

the number of units per mg protein

10

Most human enzymes have a temperature optimum of about ___ degrees celsius

37

11

Pepsin is an enzyme in the stomach and has a pH optimum of about ___. Trypsin is an enzyme active in the small intestine and has a pH optimum of about ___

2; 8

12

What type of reaction does an oxidoreductase enzyme catalyze? give some examples of oxidoreductase enzymes

oxidation-reduction reactions; dehydrogenases, oxidases, reductases, peroxidases, catalase, oxygenase, hydroxylase

13

What type of reaction does a transferase enzyme catalyze? give some examples of transferase enzymes

catalyze transfer of a group such as glycosyl, methyl, or phosphoryl; transaldolase, transketolase, acyl transferase, kinases, phosphomutases

14

What type of reaction do hydrolases catalyze? give some examples of hydrolase enzymes

catalyze hydrolytic cleavage of C-C, C-O, C-N, and other bonds; esterase's, glycosides, peptidases, phosphotases, etc

15

What type of reaction do lyases catalyze? give some examples of lyase enzymes

catalyze cleavage of C-C, C-O, C-N, and other bonds by atom elimination, leaving double bonds; decarboxylases, aldolases, hydratases, dehydratases, synthases

16

What type of reaction do isomerases catalyze? give some examples of isomerase enzymes

catalyze geometric or structural changes within a molecule; racemases, epimerases, isomerases, some mutases

17

What type of reaction do ligases catalyze? give some examples of ligase enzymes

catalyze the joining together of two molecules coupled to the hydrolysis of ATP; synthetases and carboxylases

18

Define active site

a specific region on the enzyme where the reaction occurs

19

The ___ of the enzyme is critical for the appropriate structure of the active site

structure

note: lock and key - enzyme has to fit

20

Changes in the enzyme structure (due to AA composition) may or may not have major effects on the activity of the enzyme. True or false?

true

21

In regards to catalysis by proximity, in order for molecules to react, they must come within ____ ____ distance of each other

bond forming

22

In regards to catalysis by proximity, the active site of an enzyme binds substrates creating a ___ local concentration

high

23

In regards to catalysis by proximity, the substrates are also bound in a ___ ___ conducive to reaction

specific orientation

24

In regards to acid-base catalysis, ____ functional groups of AA side chains may participate in catalysis by acting as acids and/or bases

ionizable

25

In regards to catalysis by strain, enzymes which catalyze reactions which break bonds may bind substrates in what type of manner?

in such a way to destabilize the bond to be broken

26

In regards to covalent catalysis, a ___ bond is established between substrate and enzyme

covalent

27

In regards to covalent catalysis, the covalently modified enzyme essentially then becomes a ___ for the reaction

substrate

28

In regards to covalent catalysis, the reaction of covalently modified enzyme to product is more ___ ____ than the reaction of substrate to product

energetically favorable

29

What are cofactors, coenzymes, and prosthetic groups? (in general as a group)

small, non-protein molecules and metal ions which participate directly in the enzymatic process

30

Many cofactors, coenzymes, and prosthetic groups are derived from what?

vitamins

31

Prosthetic groups are tightly and stably incorporated into the protein, sometimes by ___ bonds

covalent

32

metal ions are the most common prosthetic groups. give some examples

Co, Cu, Mg, Mn, and Zn

33

enzymes containing a metal prosthetic group are called _____

metalloenzymes

34

Pyroxial phosphate is a prosthetic group derived from what?

vitamin pyrodoxine, B6

35

Thiamine pyrophosphate is a prosthetic group derived from what?

thiamine, B1

36

FMN and FAD are prosthetic groups derived from what?

riboflavin, vitamin B2

37

Cofactors bind _____ to either the substrate or the enzyme but are nonetheless required for activity

transiently

38

What is the most common cofactor?

Mg2+

note: it is required for enzymes which involve ATP

39

Coenzymes serve as "___", accepting a group from one reaction and supplying the group in other reactions

shuttles

40

Coenzyme A transfers what?

acyl groups

41

Folates transfer what?

one carbon groups

42

Isoenzymes are physically distinct enzymes, meaning they are different proteins with different AA sequences which catalyze what?

the same reaction

43

What are some of the different properties between isoenzymes?

kinetic differences (substrate affinities), differences in activity regulation

44

Isoenzymes may be differentially expressed by different tissues. Give an example

the heart isoenzymes of creatine kinase may be distinguished form the skeletal muscle isoenzymes of creatine kinase