enzymes properties and classification, Lecture notes of Biochemistry

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CHAPTER 4 ENZYMES

• (^) Enzyme song

Learning Outcomes

• (^) Describe the general properties of enzymes
• (^) State the classification of enzymes
• (^) Describe and calculate the enzyme kinetics
• (^) Explain the enzyme inhibition

• (^) Travelling over a mountain pass is an analogy to describe the progress of chemical reaction.
• (^) Catalysts speed up the process

Enzymes are protein molecules that are manufactured by all plant and animal cells.

WHAT ARE ENZYMES?

All cells require enzymes to survive and function. Enzymes make chemical reactions go faster, but are not changed by the reaction.

• (^) Eg. digestive enzymes cause food that you eat to be broken down much faster than would occur without them, but they are not broken down in the reaction they are speeding up.

NOMENCLATURE

adding the suffix ase eg: amylase, lipase type of action and substrate name eg: Glutamate dehydrogenase, Pyruvate decarboxylase having trivial names eg: pepsin, trypsin

1. Higher reaction rates

 Enzymes increase the rate of reaction

2. Milder reaction conditions

• (^) Catalyzed reactions occur under mild conditions:
• (^) Temperature under 100°C
• (^) Atmospheric pressure (101.325 kPa)
• (^) Nearly neutral pH (pH 7.0)

4. Capacity for regulation

• (^) The mechanisms of the regulatory processes include: - (^) Allosteric control - (^) Negative feedback (Product)

• (^) Allosteric Enyme
• (^) Negative feedback (product)

Enzyme Classification 6 classes^ 6 classes

1. Oxidoreductase^ 1. Oxidoreductase 3. Hydrolase^ 3. Hydrolase 4. Lyases^ **_4. Lyases

5. Isomerase5. Isomerase
6. Ligase_**^ **_6. Ligase
7. Transferase_**^ 2. Transferase Catalyze redox reactions (transfer of e) Dehydrogenase, Oxidases, Peroxidases, reductase Catalyze transfer of functional groups (acetyl, methyl, amino etc.) Aminotransferases, acetyltransferases Catalyze hydrolysis reactions of bonds by the addition of H2O. Lipase, proteases, arginase Cleave bonds (other than hydrolysis and oxidation (CC, CO, CS, CN bonds etc) Decarboxylases, aldehyde lyases Catalyze isomerization (atomic rearrangement within a molecule) (alter structure, eg optical, structural isomers) isomerase & epimerases Catalyze the synthetic reaction (joins two molecules by forming a new bond with ATP hydrolysis) Aminoacyl tRNA synthetase

Enzyme Catalysis

How enzyme functioned as biocatalyst?

• (^) Enzyme speed up reaction but cannot alter the free energy change
• (^) Free energy (G°) = the difference between the energies of the reactants and the energy of the products
• (^) The rate of a reaction depends on its activation energy, G° ‡
• At maximum of the curve – “The transition state”

• Fig. 61a, p.

• (^) The presence of catalyst speed up the reaction by changing the mechanism and thus lowering the activation energy

Enzyme Catalysis