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Enzymes and Nucleic Acids Overview

Apr 27, 2025

Biology Unit 1.4 - Biological Reactions are Regulated by Enzymes

Metabolism

  • Metabolism: Series of enzyme-controlled reactions
  • Combination of anabolic (build-up) and catabolic (break-down) reactions

Enzymes

  • Function: Biological catalysts that speed up metabolic reactions
  • Structure: Tertiary structure proteins with a specific 3D globular shape
    • Active site formed by folding of globular proteins
    • Active site held together by peptide, disulphide, hydrogen, and ionic bonds
    • Enzymes are specific to substrates forming an enzyme-substrate complex

Properties of Enzymes

  • Biological catalysts
  • Not changed or used up in reactions
  • High efficiency and turnover rate
  • Catalyse natural reactions
  • Essential for cell reactions due to slow natural rates without them
  • Large molecules with specific shapes, few amino acids form active site

Types of Reactions

  • Catabolic: Breakdown of large molecules into smaller ones; exothermic
  • Anabolic: Build larger molecules from smaller ones; endothermic

Enzyme Theories

Lock and Key Theory

  • Substrate fits exactly into the active site
  • Supported by X-ray diffraction studies

Induced Fit Theory

  • Active site changes shape to fit substrate
  • Allows broad specificity, e.g., lysozyme enzyme

Enzyme Activity Factors

  • Temperature:
    • Low: low kinetic energy, slow reaction
    • Increase: increases reaction rate up to optimum (40°C)
    • Beyond optimum: denaturation
  • pH:
    • Narrow optimum range
    • Outside range can cause reversible or permanent changes
  • Substrate Concentration:
    • Initial increase increases rate, eventually plateaus
  • Enzyme Concentration:
    • Increase leads to more active sites and faster reactions

Enzyme Inhibitors

  • Competitive: Compete with substrate for active site
    • Reversible, structurally similar to substrate
    • Increasing substrate concentration decreases inhibitor effect
  • Non-competitive: Bind elsewhere, changing active site shape
    • Not reversible, not structurally similar

Industrial Use of Enzymes

  • Immobilised Enzymes: Fixed in place, used in industries
    • Examples: lactose-free milk, biosensors
    • Used for stability and reusability

Unit 1.5 - Nucleic Acids and Their Functions

Nucleotide Structure

  • Components: Phosphate group, pentose sugar, nitrogenous base

Types of Nucleotides

  • ATP: Energy currency, high energy bonds
    • Hydrolysis releases energy
    • Reversible reaction can reform ATP from ADP

DNA Structure

  • Double-stranded polymer of nucleotides
  • Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)
  • Complementary base pairing (A-T, C-G)
  • Anti-parallel strands

DNA Replication

  • Semi-conservative method
  • DNA helicase and polymerase involved
  • Meselson and Stahl experiment support

RNA

  • Single-stranded, shorter than DNA
  • Bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)

Types of RNA

  • mRNA: Carries genetic code from DNA to ribosomes
  • rRNA: Forms ribosomes
  • tRNA: Transfers amino acids during protein synthesis

Genetic Code

  • Triplet code, codons for amino acids
  • DNA transcribed into mRNA, translated into polypeptides

Protein Synthesis

  • Transcription: DNA to mRNA
  • Translation: mRNA decoded to polypeptides

Further Modifications

  • Polypeptides modified by addition of carbohydrates, lipids, or phosphates
  • Some proteins consist of multiple polypeptides