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Plant Physiology > 2 Enzymes > Flashcards

2 Enzymes Flashcards

1
Q

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

A

30

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2
Q

If we exclude inert materials, such as the cell wall and starch, which can account for up to _% of the dry weight of some cells, proteins and amino acids represent about _to _% of the dry weight of the living cell

A

90

60- 70

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3
Q
  • major function of proteins in metabolism is to serve as _,
  • biological catalysts that greatly increase the rates of biochemical reactions
A

enzymes

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4
Q

Enzymes have been called the “_”

A

agents of life

since they control
almost all life processes

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5
Q

Enzymes AKA

A

biological catalysts

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6
Q

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

A

the enzyme–substrate complex

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7
Q

enzymes will convert about a _ molecules of substrate to product in 1 s

A

thousand

some will convert as many as a million

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8
Q

enzymes do not change the position of the chemical equilibrium but rather _ the reaction rate

A

increase

large protein molecules that increases the rates of chemical reaction without
themselves undergoing change by 10^9
to 10^20 times

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9
Q

Enzyme as catalyst are extremely specific, that is, each of them
speeding up only _ particular reaction or class of reactions

A

one

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10
Q

protein-degrading enzyme of the stomach and its optimum pH

A

pepsin

a pH optimum around 2.0

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11
Q
  • – from hyperthermophilic (“extreme heat-loving”) archaebacterium Pyrococcus furiosus*;
  • oxidizes H2 at a temperature optimum greater than 95^0C;
  • the presence of this enzyme in Pyrococcus enables them to grow optimally at 100^0C
A

hydrogenase

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12
Q

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

A

International Union of Biochemistry

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13
Q

reactants of enzyme catalyzed reactions are called as _ and each
enzyme is quite specific in character

A

substrate

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14
Q

enzymes are made of proteins with occasional non-protein part

many enzymes need only proteins in their structure for their activity while others require one or more non-protein components called _

A

cofactors

  • nonprotein component of enzymes ;without it, enzymes will lack their catalytic activity
  • some cofactors can either be organic or metallic in nature
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15
Q

protein or polypeptide portion of the enzyme is called _

A

apoenzyme

some apoenzyme cannot catalyze a reaction without its cofactor nor can the cofactor function without an apoenzyme

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16
Q

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

A

coenzymes

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17
Q

example of these coenzymes are the electron carriers

A
  • nicotinamide adenine dinucleotide (NAD+) reduced to NADH
  • flavin adenine dinucleotide (FAD) reduced to FADH2

both are reduced in a dehydrogenation reaction

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18
Q

metal ion cofactors such as _ are sometimes referred to as metal
activators

A

Fe, Mo, Cu, and Zn

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19
Q

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

A

prosthetic groups

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20
Q

Enzyme catalysis

A

E + S -> E-S -> E + P

enzyme+substrate ->enzyme-substrate complex -> enzyme + product

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21
Q

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

A

substrate

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22
Q

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

A

active site

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23
Q

_ can also be found on active sites

A

coenzymes

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24
Q

enzymes are able to catalyze or speed up particular reactions because they _ the
amount of activation energy required to initiate the reaction

A

lower

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25
Q

catalysis occurs at the active site which is composed of the_ and the _

A

binding site
catalytic group

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26
Q

active site of an enzyme contains specific _ that form temporary bonds with the substrate

A

amino acid residues

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27
Q

active site of the enzyme occupies _ % of the total volume of the enzyme

A

~10 – 20

28
Q

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

A

active site

29
Q

the active site of the enzyme contains only _ amino acids

A

three to four

30
Q
  • location of substrates binding with the enzyme;
  • one of the two components of the active site of the enzyme;
  • bind and orient substrate molecules
A

binding site

31
Q

the binding site attracts and positions the _ while the catalytic group (the reactive side chains of amino acids or cofactors) carry out the _ reactions involved

A

substrate
bond-breaking and bond-forming

32
Q
  • location in active site where the catalysis of the chemical reaction occurs in the enzyme
A

catalytic site

33
Q

, the _ in the catalytic site of the enzyme are responsible
for catalyzing the chemical reaction

A

amino acids

34
Q

catalytic site _ the activation energy of the chemical reaction

A

reduces

35
Q

catalytic site is one of the two main components of the _ of an enzyme

A

active site

36
Q

the main function of an enzyme is to _ under physiological conditions

A

catalyze a chemical reaction

37
Q

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

A

Binding Site

38
Q

temporarily binds with the substrate

A

Binding Site

39
Q

binds and orients the substrate

A

Binding Site

40
Q

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

A

Catalytic Site

41
Q

in enzyme which catalyzes the reaction of the substrate

A

Catalytic Site

42
Q

reduces the chemical activation energy

A

Catalytic Site

43
Q

six major groups of enzymes based on type of reaction they catalyze

A
  1. oxidoreductases
  2. transferases
  3. hydrolases
  4. lyases
  5. isomerases
  6. ligases/ synthetases
44
Q

catalyze oxidation and reduction

A

Oxidoreductases

45
Q

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

A

Transferases

46
Q

catalyze hydrolysis reactions

A

Hydrolases

47
Q

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

A

Lyases

48
Q

catalyze isomerization reactions

A

Isomerases

49
Q

catalyze the joining of two
molecules

A

Ligases/ Synthetases –

50
Q

When the type of reaction is omitted, it is _.
like?

A

hydrolysis

urease, lactase

51
Q
  • explains the specificity of enzyme action by comparing the active site of an enzyme to a lock and the substrate to a key,
  • assumes that the enzyme is a rigid, three-dimensional body
A

Lock-and-Key Model

52
Q
  • 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
A

Induced-Fit Model

53
Q

reaction rates depend on the number of successful _ between substrate and enzyme molecules, which in turn depends upon their concentrations

A

collisions

54
Q

if we keep the concentration of the substrate constant, an increase in enzyme concentration would linearly _ the rate of enzyme activity

A

increase

55
Q

if we keep the concentration of the enzyme constant and increase the concentration of the substrate, there is a different scenario since rate _ continuously

A

does not
increase

56
Q

a point where the rate stays the same even with increase
substrate concentration called as the _

A

saturation point

57
Q

at saturation point, substrate molecules are bound to _ available active sites of an enzyme

A

all

58
Q
  • increasing substrate concentration _ the frequency with which the enzyme and substrate collide
  • as a result, enzyme-substrate complexes form _ and the rate of reaction _
A

increases
more quickly
increases

59
Q

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

A

saturated

  • any further increase in substrate concentration has no further effect on the reaction rate
  • *Note that if there is excess substrate (the first part of the graph) the line can be
    approximated to a straight lin
60
Q

temperature affects enzyme activity because of _ of the
three-dimensional structure of the enzyme

A

denaturation or the alteration

  • hence, the substrate may not be able to successfully fit the active sites
  • each enzyme has its own optimum temperature to work with
61
Q

pH influences the _ of substrates, _ state, and presence of charged
and uncharged free amino or carboxyl groups in the enzyme

A
  • ionization
  • denaturation
62
Q
  • a neutral carboxyl group requires a _ pH optimum
  • while an uncharged amino group needs a _ pH optimum
A

low
high

63
Q

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

A

inhibition
inhibitors

64
Q

Two types of Inhibitors

A
  1. Competitive Inhibitors
  2. Non-competitive Inhibitors
65
Q

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

A

Competitive Inhibitors

66
Q

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

A

Non-competitive Inhibitors

67
Q

Both competitive and noncompetitive inhibitors are _ , but some compounds alter the structure of the enzyme permanently and thus, make it irreversibly inactive

A

reversible

Plant Physiology (4 decks)

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