Enzymes Flashcards
What are enzymes?
- Enzymes are biological catalysts
- Almost every significant life process is dependent on
enzyme activity. . - Almost all enzymes are protein, except for a class of
RNA modifying catalysts known as ribozymes.
What is enzyme catalysis?
- In enzyme-catalyzed reactions, substrate
concentrations are usually greater than the enzyme
concentration. - Enzyme catalysis involves the binding of the
substrate to a specific site on the enzyme, (active or
catalytic site
What happens during enzyme catalysis?
- During enzyme catalysis, (ES) complex is first formed
then; proceeds to a transition state (ES*); before it
forms enzyme product complex (EP) which
dissociate to product and free enzyme. - The series of events can be shown thus:
E + S <-> ES <-> ES* <-> EP <-> E + P
What is the enzyme nomenclature?
Traditionally, enzymes were simply assigned
names by the investigator who discovered the
enzyme.
* As knowledge expanded, systems of enzyme
classification became complex.
How are enzymes classified currently?
- Currently enzymes are grouped into six
functional classes by the International Union
of Biochemists (I.U.B.). - I.U.B. gave each enzyme a unique number.
And specifies a textual name for each enzym
What are the type of enzymes classified by I.U.B?
1 Oxidoreductases Add or remove hydrogen atoms.
2 Transferases Transfer functional groups.
3 Hydrolases Add water across a bond, hydrolyzing
it.
4 Lyases Add or remove water, ammonia or
carbon dioxide across double bonds
5 Isomerases Catalyze isomerizations,
6 Ligases Join two chemical groups with the use
of energy from ATP
How is the enzyme name and number composed?
- Each enzyme is given a four digit number
specifying its class, subclass, substrate and the
type of the reaction - The enzyme’s name is comprised of the names of
the substrate (S), the product (P) and the enzyme’s
functional class.
What is another way in which enzymes are classified?
- Enzymes are also classified on the basis of their
composition. - Enzymes composed wholly of protein are known as
simple enzymes in contrast to complex enzymes,
which are composed of protein plus a relatively
small organic molecule. - Complex enzymes are also known as holoenzymes.
What are holoenzymes composed of?
- The protein component in the holoenzyme is called
apoenzyme, while the non-protein part is the
coenzyme or prosthetic group. - The prosthetic group is the small organic molecule
bound to the apoenzyme by covalent bonds - Coenzyme is the small organic molecule noncovalently bound to the apoenzym
What is the non-protien part of enzyme composed as?
- The non-protein component of an enzyme may be as
simple as a metal ion or as complex as a small nonprotein organic molecule - Many prosthetic groups and coenzymes are watersoluble derivatives of vitamins.
- Enzymes that require a metal in their composition are
known as metalloenzymes
What do coenzymes do?
- Coenzymes act as transporters of chemical
groups from one reactant to another. - The chemical groups carried can be as simple
as the hydride ion (H+ + 2e-) carried by NAD
or the mole of hydrogen carried by FAD; or
amine (-NH2) carried by pyridoxal phosphate.
How do coenzymes play a role as substrates?
- Coenzymes are chemically changed as a
consequence of enzyme action, thus can be
considered as second substrates, - Unlike usual substrates the coenzymes are
recycled to their original form when donate the
carried chemical grouping to an acceptor
molecule
How are enzymes specific?
- Enzymes are highly specific for the kind of
reaction they catalyze, - Enzymes are also specific towards the substrate,
- Some enzymes have broad substrate specificity,
How are enzymes specific about steric configuration of substrates?
- Enzymes also are generally specific for a
particular steric configuration (D and L
optical isomer) of a substrate. - The racemases are striking exception to
these generalities; they convert D isomers to
L isomers and vice versa
What are isozymes?
- Are multiple forms of an enzyme acting on
the same substrate and produce the same
product. - These are the products of genes that vary
only slightly. - Various isozymes are expressed in different
tissues of the body.
