Chapter 2

Question 1

Proteins constitute about __% of the total dry weight of typical plant cells.

Answer 1

30

Question 2

proteins and amino acids represent about __ to __% of the dry weight of the living cell excluding inert materials.

Answer 2

60 to 70

Question 3

the major function of proteins in metabolism is to serve as ___, biological catalysts that
greatly increase the rates of biochemical reactions

Answer 3

enzymes

Question 4

The most important features of enzymes are their ____,
which permits them to distinguish among very similar molecules, and their ___, which is far greater than that of ordinary catalysts.

Answer 4

specificity;
catalytic efficiency

Question 5

“agents of life”
▪ “biological catalysts

Answer 5

enzymes

Question 6

first step in enzyme catalysis is the formation of a tightly bound, noncovalent complex
between the enzyme and the substrate(s)— the ___

Answer 6

enzyme–substrate complex

Question 7

enzymes do not change the position of the ___ but rather increase the ___

Answer 7

chemical equilibrium;
reaction rate

Question 8

Two remarkable aspects of enzymes as catalysts:

Answer 8

-extremely effective (10^9
to 10^20 times increased reaction rate)
-extremely specific

Question 9

enzymes function at ambient ___and ____ and usually in a
___pH range near ___

Answer 9

temperature and atmospheric pressure;
narrow ;neutrality

Question 10

___– protein-degrading enzyme of the stomach (has a pH optimum
around ___)

Answer 10

pepsin; 2.0

Question 11

____– from hyperthermophilic (“extreme heat-loving”)
archaebacterium Pyrococcus furiosus; oxidizes H2 at a temperature
optimum greater than 95 degree C; the presence of this enzyme in Pyrococcus
enables them to grow optimally at 100 degree C.

Answer 11

hydrogenase

Question 12

hydrogenase is from the hyperthermophilic (“extreme heat-loving”)
archaebacterium ______; oxidizes __ at a temperature
optimum greater than ___degree C; the presence of this enzyme in Pyrococcus
enables them to grow optimally at __ degree C.

Answer 12

Pyrococcus furiosus;
H2;
95;
100

Question 13

enzymes are usually named after their substrates by the addition of the suffix __

Answer 13

“-ase

Question 14

each enzyme has been named in a systematic fashion, on the basis of the
reaction it catalyzes, by the ___

Answer 14

International Union of Biochemistry

Question 15

reactants of enzyme catalyzed reactions are called as ____

Answer 15

substrate

Question 16

non-protein component of enzymes

Answer 16

cofactors

Question 17

the protein or polypeptide portion of the enzyme is called ____

Answer 17

apoenzyme

Question 18

protein portion, inactive=
nonprotein portion, activator=
whole enzyme, active=

Answer 18

apoenzyme
cofactor
holoenzymes

Question 19

some cofactors can either be __ or ___ in nature

Answer 19

organic or metallic

Question 20

organic cofactors are called as ___which are transiently associated with the
apoenzyme and are themselves changed in the reaction

Answer 20

coenzymes

Question 21

example of coenzymes (electron carriers): 2

Answer 21

nicotinamide adenine
dinucleotide (NAD+);
flavin adenine dinucleotide (FAD)

Question 22

nicotinamide adenine
dinucleotide (NAD+) and flavin adenine dinucleotide (FAD) which are
reduced to NADH and FADH2 in a reaction called ___

Answer 22

dehydrogenation

Question 23

metal ion cofactors are sometimes referred to as ___

Answer 23

metal activators

Question 24

example of metal ion cofactors (4)

Answer 24

Fe, Mo, Cu, Zn

Question 25

non-protein co-factors that are more or less permanently associated with the enzyme protein are called ___

Answer 25

prosthetic groups

Question 26

the compound on which the enzyme works and whose reaction is being speed up is called the ___

Answer 26

substrate

Question 27

the substrate usually binds to the enzyme surface while it undergoes the reaction on a specific portion called the ___

Answer 27

active site

Question 28

can also be found on active sites

Answer 28

coenzymes

Question 29

enzymes are able to catalyze or speed up particular reactions because they lower the amount of ___ required to initiate the reaction

Answer 29

activation energy

Question 30

catalysis occurs at the ___ which is composed of the ___ and the ___

Answer 30

active site; binding site and catalytic group

Question 31

is the site of the enzyme where the substrate molecules bind and undergo the chemical reaction

Answer 31

active site

Question 32

contains specific amino acid residues that form temporary bonds with the substrate

Answer 32

active site

Question 33

active site of the enzyme occupies ~___% of the total volume of the enzyme

Answer 33

10 – 20

Question 34

is the most important part of the enzyme that catalyzes the chemical reaction

Answer 34

active site

Question 35

active site of the enzyme contains only ___ amino acids

Answer 35

three to four

Question 36

- location of substrates binding with the enzyme; one of the two components of the active site of the enzyme; bind and orient substrate molecules

Answer 36

binding site

Question 37

the ____ attracts and positions the substrate while the ___ carry out the bond-breaking and bond-forming reactions involved

Answer 37

binding site; catalytic group

Question 38

- location where the catalysis of the chemical reaction occurs in the enzyme

Answer 38

catalytic site

Question 39

__in the catalytic site of the enzyme are responsible for catalyzing the chemical reaction

Answer 39

amino acids

Question 40

reduces the activation energy of the chemical reaction

Answer 40

catalytic site

Question 41

refers to a location on a macromolecule or cellular structure at which chemical interaction with a specific active substance takes place

Answer 41

binding site

Question 42

refers to a portion of an enzyme molecule at which the actual reaction proceeds and is considered to consist of one or more residues or atoms in a spatial arrangement

Answer 42

catalytic site

Question 43

6 major groups/classification of enzymes

Answer 43

Oxidoreductases; Transferases Lyases Hydrolases Ligases/Synthetases Isomerases

Question 44

– catalyze oxidation and reduction

Answer 44

Oxidoreductases

Question 45

– catalyze the transfer of a group of atoms from one molecule to another

Answer 45

Transferases

Question 46

– catalyze hydrolysis reactions

Answer 46

Hydrolases

Question 47

– catalyze the addition of a group to a double bond or removal of two groups from adjacent atoms to create a double bond.

Answer 47

Lyases

Question 48

– catalyze isomerization reaction

Answer 48

Isomerases

Question 49

– catalyze the joining of two molecules

Answer 49

Ligases/ Synthetases

Question 50

e type of reaction catalyzed is often noted with a ___.

Answer 50

prefix

Question 51

two model proposed that showed how specific enzymes are

Answer 51

Lock-and-Key Model and the Induced-Fit Model

Question 52

explains the specificity of enzyme action by comparing the active site of an enzyme to a lock and the substrate to a key, however, this model assumes that the enzyme is a rigid, three-dimensional body

Answer 52

Lock-and-Key Model

Question 53

compares the active site to a glove and the substrate to a hand, that is, like a glove to a hand that accommodates the shape of the substrate

Answer 53

Induced-Fit Model

Question 54

Factors Affecting Enzyme Activity (3)

Answer 54

Enzyme and Substrate Concentrations; Temperature; pH

Question 55

there is a point where the rate stays the same even with increase substrate concentration called as the ___

Answer 55

saturation point

Question 56

at ___, substrate molecules are bound to all available active sites of an enzyme

Answer 56

saturation point

Question 57

what will happen? increasing substrate concentration... (3)

Answer 57

increases frequency of enzyme and substrate collision; enzyme-substrate complexes form more quickly; rate of reaction increases

Question 58

there is a limit as eventually there all the enzyme active sites are already occupied with substrate - the enzyme active sites become ___

Answer 58

saturated

Question 59

____affects enzyme activity because of denaturation or the alteration of the three-dimensional structure of the enzyme

Answer 59

temperature

Question 60

____influences the ionization of substrates, denaturation state, and presence of charged and uncharged free amino or carboxyl groups in the enzyme

Answer 60

pH

Question 61

a _____ requires a low pH optimum while an ___ needs a high pH optimum

Answer 61

neutral carboxyl group; uncharged amino group

Question 62

____is any process that makes an active enzyme less active or inactive which is accomplished by compounds known as ___

Answer 62

Inhibition ; inhibitors

Question 63

Two types of Inhibitors:

Answer 63

competitive; non-competitive

Question 64

– bind to the active site of an enzyme surface, thereby, preventing the real substrate to bind

Answer 64

Competitive Inhibitors

Question 65

– binds to some portion of the enzyme surface which may sufficiently alters the tertiary structure of the enzyme so that its catalytic effectiveness is slowed down

Answer 65

Non-competitive Inhibitors

Question 66

Both competitive and noncompetitive inhibitors are ____, but some compounds alter the structure of the enzyme ___and thus, make it ___

Answer 66

reversible; permanently ; irreversibly inactive