Chap 6

Question 1

enzyme function

Answer 1

provide mechanism for acceleration,regulation, and coordination of chemical reactions

Question 2

enzyme contribute to human health as

Answer 2

causes of diseases;
therapeutic targets;
indicators of disease

Question 3

enzyme as causes of diseases

Answer 3

gain, loss or change of function of ana enzyme can have pathological consequences

Question 4

enzyme as therapeutic targets

Answer 4

many therapeutic drugs target activity of specific enzymes

Question 5

enzyme as indicators of disease

Answer 5

biomarkers to inform disease susceptibility,prognosis and treatment

Question 6

enzymes are all ___except for a small group of __

Answer 6

proteins;

catalytic RNA molecules

Question 7

some enzyme’s protein component is fully __,others need___or ___for activity

Answer 7

active;
co-factors;
co-enzymes

Question 8

prosthetic group

Answer 8

a co-enzyme or co-factor that is tightly associated with the enzyme

Question 9

catalysts functions

Answer 9

lower the amount of energy required for a reaction to proceed;
speed up attainment of equilibrium but do not change equilibrium;
are unchanged by the reaction, recycled to participate in another reaction

Question 10

Circe effect

Answer 10

some enzyme are able to catalyze reaction faster than predicted by diffusion-control limits

Question 11

enzyme work by___

Answer 11

catalyze the inter-conversion of substrate and product ;

E+S<>ES<>E+P

Question 12

substrate

Answer 12

molecule to be acted upon by the enzyme

Question 13

product

Answer 13

what is produced by the enzyme

Question 14

active site

Answer 14

the portion of the enzyme responsible for binding the substrate leading to the formation of an enzyme-substrate complex

Question 15

structurally: active site is ____ formed from groups that come from ____. It takes up ____of the enzyme

Answer 15

a 3D cleft;
different parts of the polypeptide chain;
a small part of the total volume

Question 16

reaction: active sites are _______, water is usually _____ the active site.

Answer 16

unique microenvironments;

excluded from

Question 17

reaction: substrates are bound to enzyme by _____.

Answer 17

multiple weak interactions

Question 18

structure: specificity of substrate binding depends on the _____ the active site; substrate binding can cause ___ or _____.

Answer 18

precisely defined arrangement of atoms in;
induced fit;
conformation selection

Question 19

how enzyme work: by influencing ___ but not _____, therefore, didn’t influence the ____.

Answer 19

activation energy (delta G++);
free energy (delta G);
equilibrium of the reaction

Question 20

the delta G of a reaction depends only on the ___ ( ) the ____. the delta G of a reaction is independent of the _____.

Answer 20

free energy of the product;
minus;
free energy of the reactants;
steps of the transformation

Question 21

the delta G provides no information about ______.

Answer 21

rate of a reaction

Question 22

enzyme catalytic capabilities result from chemical effects 
1.\_\_\_\_
2.\_\_\_\_
and binding properties
1.\_\_\_\_\_
2.\_\_\_\_\_

Answer 22

acid/base catalysis;
covalent catalysis;
substrate binding;
transition-state stabilization;

Question 23

binding effects: binding of reactants in enzyme active sites provides ___ and ___

Answer 23

substrate specificity;

catalytic power

Question 24

substrate binding: enzyme properly __ and __ substrates, makes the formation of the transition state more __ and ___.

Answer 24

gather; position;

frequent; lowers the energy of activation

Question 25

substrate binding promotes reactions by

Answer 25

1. reducing entropy 2. removal of water molecules to expose reactive groups; 3. alignment of reactive functional groups of the enzyme with the substrate 4. distortion of substrates 5. induced fit of the enzyme in response to substrate binding

Question 26

transition-state (TS) stabilization: the essence of catalysis is stabilization of __. enzyme bind to transition state __ than substrates

Answer 26

transition state; | much more tightly

Question 27

transition-state analogs (TSAs) are _.

Answer 27

stable compounds whose structures resemble unstable transition states

Question 28

TSA application as therapeutics

Answer 28

1. competitive inhibitors | 2. generation of catalytic antibodies

Question 29

competitive inhibitors

Answer 29

bind the active site of a target enzyme active site with high affinity, preventing substrate binding

Question 30

catalytic antibodies (Abzymes)

Answer 30

antibodies generated against a TSA may also bind the substrate, catalyzing the reaction by promoting formation of the transition state

Question 31

chemical effects often involve

Answer 31

1. polar, ionizable residues at the active site | 2. anions and cations of certain a.a.

Question 32

acid-base catalysis: achieved by catalytic transfer of __. ___, with a pKa near ___, is often involved in acid/base catalysis.

Answer 32

a proton; histidine physiological pH

Question 33

covalent catalysis: involve __ steps ( ); an example will be___.

Answer 33

2; 1. forms a covalent linkage to the enzyme; 2. regenerate the free enzyme; eg. glucose-fructose+Pi<=>fructose+glucose-P

Question 34

enzyme kinetics definition:___ ; | equation:____

Answer 34

study of the rates at which reactions occur; | V= delta [P]/ delta t

Question 35

variables influence reaction rates:

Answer 35

T, pH (affects all protein) enzyme concentration substrate concentration

Question 36

initial velocity (Vo):

Answer 36

velocity at the beginning of an enzyme catalyzed reaction, prior to product accumulation

Question 37

initial velocity equation

Answer 37

Vo= [ES] k2 | k2: rate constant of formation of product from ES

Question 38

Michaelis-Menten eqution

Answer 38

Vo = _Vmax [S]_ | Km + [S]

Question 39

Km represents

Answer 39

[S] required to reach 1/2 Vmax

Question 40

Vmax represents

Answer 40

maximum velocity of the enzyme

Question 41

when [S] < Km,

Answer 41

enzymes are highly sensitive to changes in substrate concentration but have very little activity

Question 42

when [S] > Km

Answer 42

enzymes have high activity but are insensitive to changes in substrate concentration

Question 43

when [S] =Km

Answer 43

enzyme has significant activity and is responsive to changes in substrate concentration

Question 44

Lineweaver-Burke plot equation:__ | , it is used to determine___

Answer 44

1/Vo = Km/Vmax[S] + 1/Vmax; | Vmax and Km

Question 45

in the lineweaver-Burke plot, the slope= __, x-intercept = __, y-intercept = ___.

Answer 45

Km/Vmax; (-)1/Km; 1/Vmax

Question 46

enzyme turnover number (aka, __) _________, calculated by ___.

Answer 46

Kcat; equals the number of molecules of substrate converted to product per unit time under saturating conditions; Vmax / [Et]

Question 47

inhibitors can prevent formation of __ or the ___.

Answer 47

ES; | breakdown to E and P

Question 48

reversible inhibitors bind to the enzyme by ____; we will consider these classes of it: ____

Answer 48

non-covalent interactions; competitive; uncompetitive; noncompetitive

Question 49

competitive inhibitor___, they bind to ___ not ___; | Vmax ___ and Km____

Answer 49

``` resemble the substrate; free enzyme only; ES; be same ; increases ```

Question 50

uncompetitive inhibitors bind to __; Vmax ___ and Km ___.

Answer 50

ES complex only; decreases by conversion of ES to ESI; also decreases

Question 51

noncompetitive inhibitor bind to ___; Vmax __ and Km ___.

Answer 51

both E and ES; decreases; doesn't change

Question 52

irreversible enzyme inhibitors form ___ with the enzyme; ___ the enzyme; useful for study ____.

Answer 52

stable interactions or covalent bonds; permanently inactivate; reaction mechanisms

Question 53

suicidal inactivators: specific type of _____. they are initially __ but are converted to a ___ that ___ the enzyme.

Answer 53

irreversible enzyme inhibition; unreactive; reactive species; inactive

Question 54

acetylcholinesterase is a ___ that degrade ___

Answer 54

serine protease; | acetylcholine

Question 55

serine proteases serve as ____ that __ in __ substrates; also function in __ of ___.

Answer 55

``` digestive enzymes; cleave peptide bonds; protein; mediating the turnover; self proteins; ```

Question 56

serine proteases catalytic mechanism contains___ and ___

Answer 56

covalent; | acid-base catalysis

Question 57

serine proteases have a conserved catalytic mechanism based on a catalytic triad of residues.(__,__,__)

Answer 57

Asp; His; Ser

Question 58

two main methods to regulate enzyme activity:

Answer 58

1. enzyme availability (long term): location, rates of synthesis and degradation 2. enzyme activity (short term): covalent modification; non-covalent modification (allosteric)

Question 59

point of regulation: __ often inhibits __ which _______.

Answer 59

final product; the enzyme; catalyze the first unique and committed step of a branch point

Question 60

allosteric enzymes are regulated by ____ that ___ to the enzyme at ____.

Answer 60

allosteric modulators; bind non-covalently; sites distinct from the active site

Question 61

activities of allosteric regulator enzymes are changed by ___ and ___( )

Answer 61

inhibitors; activators ; modulators

Question 62

the binding of the substrate disrupts the ___ state to __ equilibrium in favor of ___

Answer 62

R (active) T(inactive) R

Question 63

threshold effect:

Answer 63

below a certain substrate concentration little enzyme activity; after the threshold has been reached the enzyme activity increases rapidly(on/off)

Question 64

allosteric enzyme activity is __ in substrate concentration ___ than are M-M enzymes of the same Vmax

Answer 64

more sensitive to changes; | near the Km

Question 65

in glycolysis, ___ is an allosteric inhibitor of phosphofructokinase 1 (PFK-1), ___ is an allosteric activator of PEK-1.

Answer 65

phosphoenolpyruvate (PEP); | ADP

Question 66

the activity of PFK-1 is responsive to____ as well as the ___ and ____.

Answer 66

substrate concentration; allosteric activator; inhibitors

Question 67

Covalent modification: regulate by the __ of a __ to change some aspect of the protein behavior. ( eg. ___, __, __)

Answer 67

``` Covalent linkage ; Modifying group; Methylation; Acetylation; Phosphorylation ```

Question 68

The most common post-translation covalent modification is through __, usually __, with one enzyme (_) catalyze has the addition of the group(__) and another enzyme (__) catalyzing its removal .

Answer 68

``` Phosphorylation; Reversible; Kinase; Phosphoryl group; Phosphatases; ```

Question 69

``` Glycogen metabolism: Glycogen synthase(__) is for ___; Glycogen phosphorylase (__) is for ___. ```

Answer 69

Anabolic; Catalyzing production of glycogen from glucose; Catabolic ; Catalyzing breakdown of glycogen into glucose

Question 70

Glycogen metabolism: Phosphorylation of both enzymes activates__ and inactivates___; Favors the ___.

Answer 70

``` Catabolic enzyme (glycogen phosphorylase); Anabolic enzyme ( glycogen synthase); The breakdown of glycogen into glucose. ```

Question 71

Glycogen metabolism: Unphosphorylation of both enzymes activates __ and inactivates ___. Favors the _____

Answer 71

``` Anabolic enzyme(glycogen synthase); Catabolic enzyme (glycogen phosphorylase); Storage of glucose within glycogen ```