enzymes Flashcards by Desiree Panghulan

A substance that speeds up a chemical reaction—without being a reactant—is called a ?

catalyst

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The catalysts for biochemical reactions that happen in living organisms are called ???

enzymes

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Enzymes are usually ???, though some ribonucleic acid (RNA) molecules act as ??? too.

proteins;
enzymes

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are organic catalyst produced by an organisms.

Enzymes

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The reactant in an enzyme-catalyzed reaction is called “???”

substrate

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The small portion of the molecule that is responsible for the catalytic action of the enzyme is the “???”

active site

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substrate entering active site of enzyme

as substrate binds to enzyme, it ???
making what?

then?

changes shape slightly;

enzyme substrate complex;

enzyme product complex

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Enzymes perform the critical task of lowering a reaction’s ???—that is, the amount of energy that must be put in for the reaction to begin.

activation energy

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Enzymes work by binding to ??? and holding them in such a way that the
??????

reactant molecules;

chemical bond-breaking and bond-forming processes take place more readily.

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Enzymes are superior to other catalysts in several ways:
(3)

They have a much greater catalytic power.
The activity of enzymes is closely regulated, whereas the catalyst is difficult to control.
Enzymes are highly specific with varying degrees of specificity

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specificity – they act on one substrate and only on that substrate.

Absolute

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specificity – such enzymes that can detect the difference between optical isomers (mirror images) and select only one of such isomers;

Stereospecificity

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specificity – enzymes that catalyze certain types of reactions; no waste or side reactions

Reaction

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specificity – enzymes that catalyze a group of substances that contain specific compounds.

Group

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Enzymes can be divided into two general structural classes:

simple
conjugated

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an enzyme composed only of protein (amino acid chains)

Simple enzyme

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an enzyme that has a nonprotein part in addition to a protein part.

Conjugated enzyme

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the protein part of a conjugated enzyme

Apoenzyme

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the non-protein part of a conjugated enzyme

Cofactor

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a biologically active conjugated enzyme produced from an apoenzyme and a cofactor

Holoenzyme

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Apoenzyme + Cofactor = ?

Holoenzyme

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Two broad categories of cofactors:

■ Simple metal ions
■ Small organic molecules

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simple metal ions are also called

inorganic

“co-factor”

minerals

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small organic molecules area also called

organic

“co-enzyme”

vitamins

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coenzymes synthesized by common metabolites

metabolite coenzymes

metabolite coenzymes include ???

nucleoside triphosphates

these molecules not only serve as energy carriers but also play a role in facilitating biochemical reactions as coenzymes

nucleoside triphosphates

metabolite coenzymes: most abundant is ???, but also include ??? and ???

ATP; uridine diphosphate glucose (UDP-glucose); S-adenosylmethionine

ATP can donate all of its three ??? groups in ??? reactions

phosphoryl; group-transfer

S-adenosylmethionine can donate its ??? group in ??? reactions.

methyl; biosynthetic

UDP-glucose is a source of ??? for synthesis of ??? in animals and ??? in plants.

glucose; glycogen; starch

are required for coenzyme synthesis and must be supplied in the diet

Vitamins

Lack of particular vitamins causes ???

disease

There are two categories of vitamins:

water-soluble lipid-soluble

vitamins required daily in diet; excess are excreted in urine

water-soluble vitamins

examples of water-soluble vitamins

B vitamins and C

vitamins that should be limited in intake; stored in fat

lipid-soluble vitamins

example of lipid-soluble vitamins

A, D, E, K

CLASSIFICATION OF ENZYMES: catalyze redox reactions dehydrogenases, oxidases, peroxidases, reductases

oxidoreductases

CLASSIFICATION OF ENZYMES: catalyze group transfer reactions; often require

transferases; coenzymes

CLASSIFICATION OF ENZYMES: catalyze hydrolysis reactions

hydrolases

CLASSIFICATION OF ENZYMES: lysis of substrate; produce contains ???

lyases; double bond

CLASSIFICATION OF ENZYMES: catalyze structural changes; isomerization

isomerases

CLASSIFICATION OF ENZYMES: ligation or joining of two substrates with input of energy; often called ??? or ???

ligases; synthetases or synthases

ligases are usually from ???

ATP hydrolysis

catalyze oxidation-reduction reactions

oxidoreductases

catalyze transfer of C, N, or P-containing groups

transferases

catalyze cleavage of bonds by addition of water

hydrolases

catalyze cleavage of C-C, C-S, and certain C-N bonds

lyases

catalyze racemization of optical or geometric isomers

isomerases

catalyze formation of bonds between carbon and O, S, N occupied to hydrolysis of high-energy phosphates

ligases

To catalyze a reaction, an enzyme will grab on (bind) to one or more ???. These molecules are the enzyme's ???.

reactant molecules; substrates

The part of the enzyme where the substrate binds is called the ???

active site

Enzymes are ??? and therefore undergo all the reactions that proteins do.

proteins

That is, enzymes can be coagulated by (4)

heat, alcohol, strong acids, and alkaloidal reagents.

The higher the temperature, the ??? the rate of reaction. The best temperature for enzyme function–the temperature at which the rate of a reaction involving an enzyme is the greatest is called the “???”.

faster; optimum temperature

Each enzyme has a pH range within which it can best function. This is called “???” for that particular enzyme.

optimum pH range

an enzyme found in gastric juice,

pepsin

an enzyme found in pancreatic juice

trypsin

If the pH of a substrate is too far from the optimum pH required by the enzyme, that enzyme ???. However, since body fluids contains ???, the pH usually does not vary too far from the optimum values.

cannot function at all; buffers

As with the all chemical reactions, the speed is increased with an increase in ???. With an increased concentration of substrate, the rate of the reaction will increase until ???.

concentration of reactants; available enzyme becomes saturated with substrate

Also with an increase in the amount of enzyme, the rate of ??? will ???, assuming an unlimited supply of substrate.

reaction; increase

any substance that will make the enzyme less active or render it inactive

inhibitors

Enzyme inhibition may be of two main types:

irreversible and reversible inhibition

inhibitors bind tightly to the enzyme and inactivate it.

Irreversible

Inhibitors which bind irreversibly to an enzyme often form a ??? to an ??? residue at or near the ???, and permanently inactivate the enzyme.

covalent bond; amino acid; active site;

Susceptible amino acid residues include ??? and ??? residues which have reactive ??? and ??? groups, respectively.

Ser and Cys; –OH and –SH

inhibition can be overcome by removing the inhibitor from the enzyme. These enzyme inhibitors can be classified as either ??? or ???

Reversible; competitive or noncompetitive

reversible inhibitor: inhibitor binds to the active site and directly blocks it

competitive inhibition

reversible inhibition: inhibitor binds to the allosteric site and changes the shape of the active site

non-competitive inhibition

REGULATION OF ENZYME ACTIVITY: - Is fairly slow (several hours), so is really too slow to be effective in eucaryotic cells. – Need something that can occur in seconds or less.

regulation of rate of synthesis or degradation

REGULATION OF ENZYME ACTIVITY: Done through allosteric sites or regulatory sites on enzymes

allosteric regulation

regulation of rate of synthesis or degradation is Usually done through ??? enzymes and occur in ??? early or at first committed step

regulatory; metabolic pathways

site other than active site where inhibitor or activator can bind.

allosteric sites or regulatory sites

Properties of allosteric enzymes: ■ sensitive to ??? ■ binding is ???; not chemically altered by ??? ■ regulatory enzymes possess ??? - individual polypeptide chains may or may not be identical ■ enzyme has at least one substrate that gives ??? due to positive cooperativity because of ???

■metabolic inhibitors and activators ■ noncovalent; enzyme ■ quaternary structure - individual polypeptide chains may or may not be identical ■ sigmoidal curve; multiple substrate binding sites

enzymes Flashcards

(75 cards)