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.
What is the best studied set of isozymes?
- The best studied set of isozymes is the
lactate dehydrogenase (LDH). - LDH is a tetrameric enzyme composed of all
possible arrangements of two different
protein subunits (H) for heart and (M) for
skeletal muscle.
What are the isoforms of lactate dehydrogenase
- HHHH Isoenzyme-1 Heart
- HHHM Isoenzyme-2
- HHMM Isoenzyme-3
- HMMM Isoenzyme-4
- MMMM Isoenzyme-5 Muscle
How are enzyme substrate reactions explained?
- Two models were proposed to explain the
nature of enzyme substrate binding. - The Key and lock model
- The induced fit model
How does the induced fit model explain enzyme substrate interactions?
The induced fit model proposes that the
initial interaction between enzyme and
substrate is relatively weak, and not
necessarily complementary but it induces
conformational changes in the enzyme
