Enzyme Structure and Composition

Study Notes

Enzymes are proteins that act as catalysts, speeding up chemical reactions without undergoing any change themselves.
All enzymes are proteins, but not all proteins are enzymes.
Enzymes are required in very small quantities.
Each enzyme is very specific and only attaches to one type of molecule, known as its substrate.
Enzymes possess an active site, where interaction with the substrate takes place.

Catalytic property: a small amount of enzyme is enough to break large molecules down into smaller molecules.
Specificity: enzymes are very specific in action, with one enzyme acting only on a particular substrate.
Reversibility: most reactions catalyzed by enzymes are reversible.
Sensitivity to temperature: enzymes are thermolabile or very sensitive to heat and temperature.
Specificity to pH: enzymes show maximum activity at an optimum pH of 6-8.

Essential for respiration, digestion of food, DNA replication, muscle contraction, and nerve function.
Store and release energy (ATP).
Create larger molecules from smaller ones.
Hormone production.
Transporting materials around a cell.

Endoenzymes: function within cells, most enzymes are this type. Example: metabolic oxidase.
Exoenzymes: liberated by cells and catalyze reactions outside the cell. Examples: digestive enzymes (amylase, lipase, protease).

Coenzymes: organic non-protein molecules that bind to the enzyme and participate in the reaction by carrying electrons or hydrogen atoms.
Cofactors: non-proteinous substances that associate with enzymes and are essential for their functioning.
Holoenzyme: consists of Apoenzyme + prosthetic group.
Apoenzyme: the protein part of the enzyme.
Prosthetic groups: cofactors tightly bound to an enzyme at all times. Example: FAD.

Zymogen: the inactive form of an enzyme. Example: pepsinogen → HCl → pepsin (active).
Enzyme nomenclature:
- Trivial name: such as trypsin and pepsin.
- Adding suffix "ase" to the substrate, such as maltase and lactase.
- International Union of Biochemistry (IUB) systematic name, indicating:
  - Substrate acted upon.
  - Coenzyme involved in the reaction.
  - Type of reaction catalyzed.

Oxidoreductases: catalyze oxidation and reduction reactions. Example: pyruvate dehydrogenase.
Isomerases: catalyze the formation of an isomer of a compound.
Transferases: catalyze the transfer of a chemical group from one to another compound. Example: transaminase.
Hydrolases: catalyze the hydrolysis of a bond. Example: pepsin.
Lyases: catalyze the breakage of bonds without hydrolysis. Example: aldolase.
Ligases: catalyze the joining of two molecules. Example: DNA ligase.