1. Enzymes Enzymes as Biological Catalysts
Nomenclature and Names of Enzymes
Nature of Enzymes
Enzyme Cofactors
Classification of Enzymes
Mechanism of Action
Enzyme Specificity
Enzyme Catalyzed Reaction

2. Enzymes Large molecules which most are proteins
Activity lost if denatured
Catalysts for biological reactions
Have unique three-dimensional shapes that fit the shapes of reactants.
They remain unchanged at the end of the reaction

3. Enzymes are Biological Catalysts
Enzymes are proteins that:
Increase the rate of reaction by lowering the energy of activation.
Catalyze nearly all the chemical reactions taking place in the cells of the body.

4. Nomenclature and Names of Enzymes
The name of an enzyme:
Usually ends in –ase.
Identifies the reacting substance.
Sucrase catalyzes the hydrolysis of sucrose.
Lipase catalyzes the hydrolysis of lipids.
Describes the function of the enzyme.
Oxidases catalyze oxidation.
Hydrolases catalyze hydrolysis.
Could be a common name, particularly for the digestion enzymes such as pepsin and trypsin.

5. Nature of Enzymes Simple enzymes: Complex enzymes:
composed of whole protein e. g. Ribonuclease
Complex enzymes:
composed of protein PLUS a relatively small organic / inorganic compound

6. Nature of Enzymes Holoenzyme: (Apoenzymes + Cofactor)
Cofactors: small non-protein molecules that required for the catalytic activity of the enzyme termed as "helper molecules". It may be:
Prosthetic groups are small organic or inorganic molecules that tightly bound to Apoenzyme by covalent bond. Organic like vitamins , while inorganic like metal ions (Fe++, Zn++ or Cu++).
Coenzymes: Are organic molecules loosely bound in a dissociable manner to Apoenzyme. It serves as recyclable shuttles that transport substrates from the site of generation to site of utilization e. g FAD ,NAD and vitamin B-complex .

7. Metal Ions as Cofactors
Many active enzymes require a metal ion.
Zn2+, a cofactor for carboxypeptidase, stabilizes the carbonyl oxygen during the hydrolysis of a peptide bond.

8. Some Enzymes and Their Cofactors

9. Classification of Enzymes
Enzymes are classified according to the reaction they catalyze.
Reactions catalyzed
Class
Oxidation-reduction. Add or remove hydrogen atoms.
Oxidoreductases
Transfer groups or atoms between donor and acceptor molecules.
Transferases
Hydrolysis by adding water across a bond.
Hydrolases
Add/remove atoms to form a double bond.
(Adding ammonia, or carbon dioxide across double bonds or remove them forming double bonds).
Lyases
Rearrange atoms
Isomerases
Two chemical groups are joined (or ligated) with the use of energy from ATP
Ligases

10. Oxidoreductases and Transferases

11. Oxidoreductases
Include all enzymes that catalyze oxidation reduction reaction between two substrates
Dehydrogenases
Oxidases
Reductases

12. Transferases
Catalyze the transfer of a functional group from one molecule (donor) to another (acceptor)
Transaminases catalyze transfer of an amino group
Kinases (phosphotransferases) catalyze transfer a phosphate group

13. Hydrolases and Lyases

14. Isomerases and Ligases

15. Mechanism of Action Active Site
Is a region within an enzyme that fits the shape of molecules called substrates.
Contains amino acid R groups that align and bind the substrate.
Releases products when the reaction is complete.

16. Lock & Key Model In the lock-and-key model of enzyme action:
The active site has a rigid shape.
Only substrates with the matching shape can fit.
The substrate is a key that fits the lock of the active site.

17. Induced-fit Model In the induced-fit model of enzyme action:
The active site is flexible, not rigid.
The shapes of the enzyme, active site, and substrate adjust to maximum the fit, which improves catalysis.
There is a greater range of substrate specificity.

18. Enzyme Specificity Enzymes may recognize and catalyze:
A single substrate.
A group of similar substrates.
A particular type of bond.

19. Isoenzymes
Isoenzymes group of enzymes differs in amino acid sequence ( structure) but catalyze the same reaction in different tissues in the body.
Lactate dehydrogenase, which converts lactate to pyruvate, (LDH) consists of five isoenzymes.

21. Enzyme Catalyzed Reaction

22. Enzyme Catalyzed Reaction
The proper fit of a substrate (S) in an active site forms an enzyme-substrate (ES) complex.
E + S ES
Within the ES complex, the reaction occurs to convert substrate to product (P).
ES E + P
The products, which are no longer attracted to the active site, are released.
Overall, substrate is convert to product.
E + S ES E + P

23. Enzyme Catalyzed Reaction
K1 [E][S]=K-1[ES] +K2 [ES]
Keq = K1 [E] [S]-K-1[ES] -K2[ES]= 0
Michaelis-Menten equation
V° = Vmax [S]/[S]+Km
Michaelis-Menten Constant
Km = K2 + K-1 / K1

24. Michaelis-Menten Curve

25. Substrate Saturation of an Enzyme
A. Low [S] B. 50% [S] or Km C. High, saturating [S]