Lecture 4

Question 1

enzymes

Answer 1

complex biological molecules that behave as biological catalysts

Question 2

functions of enzymes

Answer 2

-highly specialized proteins
-can accelerate chemical reactions

Question 3

active site

Answer 3

one region on the enzyme directly responsible for interactions with the reacting molecules

Question 4

enzyme classification:

oxidation-reduction reactions

Answer 4

oxidoreductases

Question 5

enzyme classification:

transfer of functional groups

Answer 5

transferases

Question 6

enzyme classification:

hydrolysis reactions

Answer 6

hydrolases

Question 7

enzyme classification:

group elimination to form double bonds

Answer 7

lyases

Question 8

enzyme classification:

isomerization

Answer 8

isomerases

Question 9

enzyme classification:

bond formation coupled with ATP hydrolysis

Answer 9

ligases

Question 10

ligand

Answer 10

molecules that reversibly binds to a macromolecules

Question 11

what are the two things interaction specificity between ligand and enzyme are based on?

Answer 11

shape (geometric), charge (electronegativity)

Question 12

the _ _____ of amino acids contribute to the shape and charge of both the ligand and the enzyme active sites

Answer 12

R groups

Question 13

where does enzyme catalysis occur?

Answer 13

binding or active site

Question 14

an enzyme and substrate can be modeled as a …

Answer 14

lock and key

Question 15

what are the 2 models of ligand binding?

Answer 15

lock and key, induced fit model

Question 16

which model is this?

the shape of a ligand or substrate must match exactly to the shape of the active site of an enzyme

Answer 16

lock and key model

Question 17

which model is this?

a loosely bound ligand can interact with functional groups on the protein and cause the protein to alter its conformation so as to better fit and bind the ligand more tightly

Answer 17

induced fit model

Question 17

how do enzymes accelerate reactions?

Answer 17

by stabilizing the transition state and reducing the free energy of the transition state

Question 17

in the induced model, the enzyme can be seen as …

Answer 17

clay because of how it will mold to the substrate’s form

Question 18

what type of catalysis is a proton donor?

Answer 18

acid catalysis

Question 19

what type of catalysis is a proton acceptor?

Answer 19

base catalysis

Question 20

covalent catalysis

Answer 20

a transient covalent bond forms between the enzyme and the substrate during formation of the transition state

Question 21

simply binding substrates facilitates reactions in 2 ways:

Answer 21

1. bring substrates into contact with each other and catalytic groups
   2.enzymes bind substrates with a specific orientation that aligns the substrate and catalytic groups

Question 22

what kind of catalysis involves metals tightly bound to the enzyme?

Answer 22

metal ion catalysis

Question 23

what are common metal cofactors?

Answer 23

Fe2+, Fe3+, Cu2+, Mn2+, Co2+

Question 24

what kind of reversible changes do metal ions do to mediate oxidation-reduction reactions?

Answer 24

-the metal’s oxidation state
-orient the substrate for reaction
-stabilize or shield negative charges

Question 25

digestive enzymes that cleave peptide bonds have _____ catalytic mechanisms but _____ in substrate specificity

Answer 25

similar; differ

Question 26

what type of curve results from when an enzyme becomes saturated as [S] increases

Answer 26

hyperbolic

Question 27

Km measures…

Answer 27

substrate concentration

Question 28

what is Km inversely related to?

Answer 28

the affinity of an enzyme for its substrate

the higher the affinity the lower the Km

Question 29

what is the Michaelis-Menten equation?

Answer 29

V0= Vmax[S]
————
Km+[S]

Question 30

What is the catalytic constant or Turnover number?

Answer 30

Kcat

Question 31

what does Kcat describe?

Answer 31

-describes how quickly an enzyme can act
-how fast the ES complex proceeds to E + P

Question 32

what does Kcat/Km represent?

Answer 32

catalytic efficiency

Question 33

what does the catalyic efficiency describe?

Answer 33

-how avidly the enzyme binds its substrate
-how rapidly it converts it to product

Question 34

what are two types of enzyme inhibition?

Answer 34

irreversible and reversible

Question 35

what kind of inhibition results from binding to the enzyme so tightly that activity is blocked?

Answer 35

irreversible inhibition

Question 36

what are the 3 types of reversible inhibition?

Answer 36

competitive, uncompetitive, mixed

Question 37

small molecules that bind an enzyme at sits different than the substrate binding site and effects, positively or negatively, the activity of that enzyme

Answer 37

allosteric effectors

Question 38

what are the two types of allosteric effectors?

Answer 38

allosteric activators
allosteric inhibitors

Question 39

1 molecule acts as both the ligand and the allosteric modulator

Answer 39

homotropic enzyme

Question 40

modulators are different than ligands with different binding sites

Answer 40

heterotrophic enzyme

Question 41

what preferentially binds to a high affinity R state

Answer 41

ATP

Question 42

what preferentially binds to a low affinity T state

Answer 42

CTP