CHAPTER 2: Plant Cell and Enzymes Flashcards by jy d

constitute about 30% of the total dry weight of typical plant cells.

protein

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Proteins and amino acids represent about __ to ___ of the dry weight of the living cell.

60 to 70%

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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

90%

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Major function of proteins in metabolism is to serve as

enzymes

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greatly increase the rates of biochemical reactions, making life possible

enzymes, biological catalysts

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Do enzymes change when they participate themselves in processes?

They do not change

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Enzymes participate
in these reactions but are not themselves ____changed in the process.

fundamentally

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Enzymes have been called the

“agents of life”

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The most important features of enzymes are their (2)

specificity
catalytic efficiency

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Feature of enzyme which permits them to distinguish among very similar molecules

specificity

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____ are _____ where continuous
synthesis and degradation of molecules happen and hasten by catalysts

plants cells
metabolic machineries

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Enzymes has the ability to discriminate between similar molecules results from the fact that the first step in enzyme catalysis is the formation of

tightly bound, noncovalent complex between the enzyme and the substrate(s)— the enzyme–substrate complex

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Enzymes are unique in the ____ ___ ___ they bring about, orders of magnitude greater than those effected by other catalysts

large rate enhancements t

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enzymes will convert about a thousand molecules of substrate to product in__, while some will convert as many as a _____

1 s
million

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large protein molecules that increases the rates of chemical reaction without themselves undergoing change

Enzyme

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Enzyme do not change the position of the _______ ____ but rather increase the reaction rate

chemical equilibrium

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Two remarkable aspects of enzymes as catalysts:

-increasing the reaction rates from 109 to 1020 times
-extremely specific

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Enzyme as catalyst are extremely effective by increasing the reaction
rates from ______ to ___ times

10^9 to 10^20 times

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Enzyme as catalyst are_____, that is, each of them speeding up only __ or ____

extremely specific

one particular reaction or class of reactions

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Enzymes function at _____ and ________ and usually in a
narrow pH range near _____

ambient temperature
atmospheric pressure
neutrality

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few enzymes are able to function under ___

extremely harsh conditions

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

pepsin

2.0

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from hyperthermophilic (“extreme heat-loving”) archaebacterium Pyrococcus furiosus; oxidizes H2 at a temperature optimum greater than 950C; the presence of this enzyme in Pyrococcus enables them to grow optimally at 1000C.

hydrogenase

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hydrogenase – from hyperthermophilic (“extreme heat-loving”) archaebacterium

Pyrococcus furiosus

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Enzymes are usually named after their __ by the addition of the suffix ____

substrates “-ase”

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

International Union of Biochemistry

the versatility of enzymes reflects their properties as

proteins

enzymes are

biological catalyst

enzymes are biological catalyst ; they ___ the rate of chemical reactions by taking place ____ without themselves undergoing any change

increase within living cells

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

substrate

enzymes are made of ___with occasional ___ part

proteins non-protein

non-protein component of enzymes

cofactors

without cofactors, enzymes will lack their

catalytic activity

the protein or polypeptide portion of the enzyme is called

apoenzyme

some ____ cannot catalyze a reaction without its ____ and vice versa

apoenzyme cofactor

some cofactors can either be ____ or ____ in nature

organic or metallic

____are called as coenzymes which are transiently associated with the apoenzyme and are themselves changed in the reaction

organic cofactors

dehydrogenation reaction -nicotinamide adenine dinucleotide (NAD+) -flavin adenine dinucleotide (FAD)

NADH and FADH2

metal ion cofactors such as Fe, Mo, Cu, and Zn are sometimes referred to as

metal activators

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

prosthetic groups

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

substrate

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

active site

can also be found on active sites

coenzymes

enzymes are able to catalyze or speed up particular reactions because they _____required to initiate the reaction

lower the amount of activation energy

catalysis occurs at the active site which is composed of the__ and ___

binding site and the catalytic group

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

active site

active site of an enzyme contains ___ ____ ____ ____ that form temporary bonds with the substrate

specific amino acid residues

active site of the enzyme occupies ____ of the total volume of the enzyme

~10 – 20%

active site is the most important part of the enzyme that catalyzes the

chemical reactions

he active site of the enzyme contains only __ to ____

three to four amino acids

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

binding site

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

catalytic site

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

amino acids

catalytic site ____ the activation energy of the chemical reaction

reduces

____ is one of the two main components of the active site of an enzyme

catalytic site

the main function of an enzyme is to catalyze a chemical reaction under

physiological conditions

refers to a location on a macromolecule or cellular structure at which chemical interaction with a specific active substance takes place temporarily binds with the substrate binds and orients the substrate

binding site

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 catalyzes the reaction of the substrate reduces the chemical activation energy

catalytic site

Six major classifications of enzymes

-(HOT ILL) -hydrolases -oxidoreductases -transferases -isomerases -lyases -ligases/synthetases

The suffix – ase identifies a ____ as an enzyme

substance

The type of reaction catalyzed is often noted with a

prefix

The substrate is often

noted

Enzyme Naming (3)

1. The suffix – ase identifies a substance as an enzyme. 2. The type of reaction catalyzed is often noted with a prefix. 3. The substrate is often noted. -

enzymes are ___ ____protein catalysts for each enzyme has its own uniquely shaped active site which is specific to certain type of substrate

highly specific

accordingly, two model were proposed that showed how specific enzymes are including the (2)

Lock-and-Key Model - Induced-Fit Model

a model for enzyme-substrate interaction in which the active site of the enzyme does not completely fit to the substrate

induced fit model

Enzyme-substrate interaction in which the active site of the enzyme completely fits with the substrate

lock and key model

induced fit model was suggested by

Daniel Koshland

lock and key model was suggested by

Emil Fischer

The active site of the enzyme does not completely fit with the substrate in the

induced fit model

active site of the enzyme precisely fits with the substrate in the

lock and key model

In this model, the active site of the enzyme has to undergo a conformational change to improve binding

induced fit model

model that describes the specificity of the active site of the enzyme to a particular substrate.

lock and key model

The active site of the enzyme contains two components in the

induced fit model

the active site of the enzyme contains a single entity in the

lock and key model

model where there is a separate catalytic group in the enzyme

induced fit model

model where there is no separate catalytic group in the enzyme

lock and key model

Model where the active site of the enzyme is not static

induced fit model

Model where the active site of the enzyme is static in

lock and key model

transition state develops before the reactants undergo changes in the

induced fit model

a transition state does not develop before the reactants undergo changes in the

lock and key model

Catalytic group weakens the substrate bonds either by the nucleophilic or electrophilic attack in the

induced fit model

the catalytic group does not weaken the substrate bonds in the

lock and key model

describes the mechanism of nonaction over competitive inhibitors

induced fit model

describes the specificity of the active site of the enzyme to a particular substrate

lock and key model

_____ 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 ___, ____

Lock-and-Key Model rigid, three-dimensional body

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

Induced-Fit Model

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

successful collisions

Factors affecting the Enzyme Activity and Inhibition (3)

-Enzyme and Substrate Concentrations -Temperature -pH

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

substrate

if we keep the concentration of the _____ constant and increase the concentration of the substrate, there is a different scenario since rate does not increase continuously

enzyme

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

saturation point

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

saturation point

increasing _____increases the ____ with which the enzyme and substrate collide

substrate concentration frequency

Because of the increased collision of enzyme and substrate, enzyme-substrate complexed _______ and the rate of reaction ____

form more quickly increases

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

saturated

any further increase in substrate concentration has __ ____ ____ on the reaction rate

no further effect

increasing the amount of _____also increases the _____ of with which the enzyme and substrate collide

enzyme frequency

some enzymes become_____as they won't have any substrate to bind

redundant

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

temperature

Causes denaturation or alteration making the substrate not be able to fit to active sites

temperature

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

a neutral carboxyl group requires a ____ optimum while an uncharged amino group needs a ____ optimum

low pH high pH

any process that makes an active enzyme less active or inactive

inhibition

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

inhibitors

Two types of Inhibitors:

-Competitive Inhibitors -Non-competitive Inhibitors

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

-Competitive Inhibitors

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

Non-competitive Inhibitors

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

reversible irreversibly inactive