Enzymes

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🔹 What Are Enzymes?

Enzymes are biological catalysts that speed up chemical reactions without being consumed.

They are mostly proteins (some are RNA-based – ribozymes).

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🔹 Basic Properties

Property Description

Specificity Each enzyme acts on a specific substrate.

Reusable Not used up in the reaction.

Sensitive to conditions Affected by pH, temperature, and inhibitors.

Lower activation energy Speeds up reactions by lowering the energy required.

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🔹 Enzyme Structure

Active site: Part of enzyme where the substrate binds.

Substrate: The molecule upon which the enzyme acts.

Enzyme-substrate complex: Temporary complex formed during the reaction.

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🔹 Enzyme-Substrate Interaction Models

1. Lock and Key Model: Active site fits the substrate exactly.

2. Induced Fit Model: Enzyme changes shape to bind the substrate more effectively.

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🔹 Factors Affecting Enzyme Activity

Factor Effect

Temperature Too high = denaturation, optimal range varies.

pH Most enzymes work best at specific pH (e.g., pepsin at pH 2, amylase at pH 7).

Substrate concentration More substrate = faster reaction (up to saturation).

Enzyme concentration More enzyme = faster rate (if substrate available).

Inhibitors Can reduce or stop enzyme activity.

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🔹 Enzyme Inhibition

Type Description

Competitive Inhibitor competes with substrate for active site.

Non-competitive Inhibitor binds elsewhere, changing enzyme shape.

Irreversible Inhibitor permanently inactivates enzyme.

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🔹 Enzyme Classification (by reaction type – 6 major classes)

Class Function Example

Oxidoreductases Redox reactions (e.g., dehydrogenase)

Transferases Transfers groups (e.g., kinase)

Hydrolases Break bonds with water (e.g., protease)

Lyases Break bonds without water

Isomerases Rearrange atoms in molecule

Ligases Join molecules using ATP (e.g., DNA ligase)

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🔹 Examples of Important Enzymes

Enzyme Function

Amylase Breaks starch into sugars

Lipase Breaks down fats

Pepsin Breaks down proteins in stomach (acidic)

DNA polymerase Synthesizes DNA strands

Lactase Breaks down lactose into glucose & galactose

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🔹 Clinical and Pharmaceutical Importance

Enzyme deficiencies cause diseases (e.g., Lactose intolerance, G6PD deficiency).

Enzymes as drugs: e.g., Streptokina

se (for clot breakdown).

Enzyme inhibitors: e.g., ACE inhibitors for hypertension, statins for cholesterol.