SHS.133. 7 Enzymes

Course Information

  • Course Code: SHS.133/SHS.115

  • Credit Hours: 3 (2-1)

  • Lecture by: Mouvez Zeeshan, M.Phil Microbiology

  • Institution: BS (Hons) Medical Lab Technology, UHS

  • Membership: Pakistan Association of Medical Lab Scientists (MPAMLS)

  • Reference Textbooks:

    • Lehninger: Principles of Biochemistry

    • Essentials of Medical Biochemistry by Mushtaq Ahmed

    • Principles of Biochemistry

Outlines

  • Catalyst

  • Biological Catalyst

  • Importance of Enzymes

  • Naming of Enzymes

  • Enzyme Classification

  • Properties of Enzymes

  • Mode of action of Enzymes

Enzymes

  • Definition: Derived from the Greek "en" (in) and "zyme" (leaven, meaning ferment).

  • Key Features: Catalytic properties discovered in yeast cells involving a substrate and active site.

Catalyst

  • Definition: An agent increasing the reaction rate of other substances without being altered or destroyed.

Biological Catalysts (Enzymes)

  • Nature: All enzymes are proteins (except ribozymes).

  • Function: Speed up reactions by lowering activation energy.

  • Characteristics: Not altered, reused in reactions.

Importance of Enzymes

  • Role in Metabolism: All biochemical reactions are enzyme-catalyzed.

  • Diagnostic Importance: Blood enzyme levels indicate various diseases (e.g., liver disorders, myocardial infarction).

  • Therapeutic Use: Used in digestive processes and blood coagulation.

Naming of Enzymes

Enzyme Nomenclature

  • Common Names: May end in -ase, often reference substrate or function (e.g., sucrase, oxidase).

  • Systematic Names: Classified using EC numbers, e.g., EC (2.7.1.1) for hexokinase.

Enzyme Classification (EC System)

  1. EC 1: Oxidoreductases - Catalyze oxidation/reduction.

  2. EC 2: Transferases - Transfer functional groups.

  3. EC 3: Hydrolases - Hydrolyze bonds by adding water.

  4. EC 4: Lyases - Cleave bonds by means other than hydrolysis.

  5. EC 5: Isomerases - Catalyze isomerization changes within a molecule.

  6. EC 6: Ligases - Join two molecules with covalent bonds using ATP.

Properties of Enzymes

Specificity

  • Varying degrees of specificity based on substrate recognition.

Regulation

  • Enzyme activity can be regulated (induction/repression) through regulatory sites.

Location within Cells

  • Enzymes are often localized to specific organelles for functional significance.

Catalytic Efficiency

  • Reactions proceed 10^3 to 10^8 times faster than uncatalyzed reactions, characterized by turnover number.

Active Site

  • The region where substrates bind to the enzyme, often small compared to the enzyme's full size.

Isozymes

  • Distinct enzymes that catalyze the same reaction under different conditions or locations.

Holoenzyme vs Apoenzyme

  • Holoenzyme: Active enzyme with non-protein component.

  • Apoenzyme: Inactive enzyme without non-protein component.

Cofactors

  • Non-protein components necessary for enzyme activity:

    • Coenzymes: Loosely bound (e.g., NAD+).

    • Prosthetic Groups: Tightly bound (e.g., metal ions).

Proenzymes/Zymogens

  • Inactive precursor forms that become active through other enzymes or substances.