enzymes Flashcards
A substance that speeds up a chemical reaction—without being a reactant—is called a ?
catalyst
The catalysts for biochemical reactions that happen in living organisms are called ???
enzymes
Enzymes are usually ???, though some ribonucleic acid (RNA) molecules act as ??? too.
proteins;
enzymes
are organic catalyst produced by an organisms.
Enzymes
The reactant in an enzyme-catalyzed reaction is called “???”
substrate
The small portion of the molecule that is responsible for the catalytic action of the enzyme is the “???”
active site
substrate entering active site of enzyme
as substrate binds to enzyme, it ???
making what?
then?
changes shape slightly;
enzyme substrate complex;
enzyme product complex
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
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.
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
specificity – they act on one substrate and only on that substrate.
Absolute
specificity – such enzymes that can detect the difference between optical isomers (mirror images) and select only one of such isomers;
Stereospecificity
specificity – enzymes that catalyze certain types of reactions; no waste or side reactions
Reaction
specificity – enzymes that catalyze a group of substances that contain specific compounds.
Group
Enzymes can be divided into two general structural classes:
simple
conjugated
an enzyme composed only of protein (amino acid chains)
Simple enzyme
an enzyme that has a nonprotein part in addition to a protein part.
Conjugated enzyme
the protein part of a conjugated enzyme
Apoenzyme
the non-protein part of a conjugated enzyme
Cofactor
a biologically active conjugated enzyme produced from an apoenzyme and a cofactor
Holoenzyme
Apoenzyme + Cofactor = ?
Holoenzyme
Two broad categories of cofactors:
■ Simple metal ions
■ Small organic molecules
simple metal ions are also called
inorganic
“co-factor”
minerals
small organic molecules area also called
organic
“co-enzyme”
vitamins
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
