Enzyme Catalysis

Question 1

Enzymes are biological catalysts. Describe what a catalyst does

Answer 1

increases rate of reaction but does not effect the equilibrium constant

Question 2

A catalyst decreases activation energy. True or false?

Answer 2

true

Question 3

Does an enzyme effect the free energy of a reaction?

Answer 3

no

Question 4

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

Answer 4

10^6 - 10^12; 10^3

Question 5

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

Answer 5

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

Question 6

Enzymatic reactions have tremendous reaction specificity that results in what?

Answer 6

very rarely occurring side products

Question 7

True or false?

Enzyme activity can vary in response to biological molecules other than the enzyme’s substrates or products

Answer 7

true

Question 8

What is a unit of enzyme activity?

Answer 8

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

Question 9

What is a specific activity of an enzyme?

Answer 9

the number of units per mg protein

Question 10

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

Answer 10

37

Question 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 ___

Answer 11

2; 8

Question 12

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

Answer 12

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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

Define active site

Answer 18

a specific region on the enzyme where the reaction occurs

Question 19

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

Answer 19

structure

note: lock and key - enzyme has to fit

Question 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?

Answer 20

true

Question 21

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

Answer 21

bond forming

Question 22

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

Answer 22

high

Question 23

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

Answer 23

specific orientation

Question 24

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

Answer 24

ionizable

Question 25

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

Answer 25

in such a way to destabilize the bond to be broken

Question 26

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

Answer 26

covalent

Question 27

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

Answer 27

substrate

Question 28

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

Answer 28

energetically favorable

Question 29

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

Answer 29

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

Question 30

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

Answer 30

vitamins

Question 31

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

Answer 31

covalent

Question 32

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

Answer 32

Co, Cu, Mg, Mn, and Zn

Question 33

enzymes containing a metal prosthetic group are called _____

Answer 33

metalloenzymes

Question 34

Pyroxial phosphate is a prosthetic group derived from what?

Answer 34

vitamin pyrodoxine, B6

Question 35

Thiamine pyrophosphate is a prosthetic group derived from what?

Answer 35

thiamine, B1

Question 36

FMN and FAD are prosthetic groups derived from what?

Answer 36

riboflavin, vitamin B2

Question 37

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

Answer 37

transiently

Question 38

What is the most common cofactor?

Answer 38

Mg2+ note: it is required for enzymes which involve ATP

Question 39

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

Answer 39

shuttles

Question 40

Coenzyme A transfers what?

Answer 40

acyl groups

Question 41

Folates transfer what?

Answer 41

one carbon groups

Question 42

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

Answer 42

the same reaction

Question 43

What are some of the different properties between isoenzymes?

Answer 43

kinetic differences (substrate affinities), differences in activity regulation

Question 44

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

Answer 44

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