Lecture Notes: Proteins and Nucleic Acids

Proteins

• Constituents of Cells:

  • Make up more than 50% of the dry mass of most cells.
  • Provide support, communication, movement, transport, and defense against disease.

• Functions of Proteins:

  • Enzymatic Proteins:
    • Act as biological catalysts.
    • Example: Digestive enzymes break down molecules like sucrose into glucose and fructose.
  • Storage Proteins:
    • Store amino acids for developing embryos.
    • Examples: Casein in milk, storage proteins in seeds like ovalbumin in egg white.
  • Defensive Proteins:
    • Example: Antibodies protect against disease.
  • Transport Proteins:
    • Example: Hemoglobin transports oxygen; transport proteins in cell membranes facilitate diffusion.
  • Hormonal Proteins:
    • Example: Insulin helps cells uptake sugar, balancing blood sugar levels.
  • Contractile and Motor Proteins:
    • Involved in movement; examples in muscle tissue.
  • Receptor Proteins:
    • Respond to chemical stimuli, crucial at neuromuscular junctions.
  • Structural Proteins:
    • Examples: Keratin in hair, collagen in connective tissue.

• Enzymes:

  • Speed up chemical reactions without being consumed.

• Protein Structure and Formation:

  • Composed of polypeptides, chains of amino acids.
  • Amino Acids:
    • Organic molecules with carboxy and amino groups.
    • Differ due to "R groups" or side chains which affect properties and shape.
  • Peptide Bonds:
    • Link amino acids by connecting carboxy and amino groups.
  • Levels of Protein Structure:
    • Primary Structure: Sequence of amino acids.
    • Secondary Structure: Coils and folds due to hydrogen bonds; includes alpha helix and beta pleated sheet.
    • Tertiary Structure: Interactions among R groups; hydrogen bonds, ionic bonds, hydrophobic interactions.
    • Quaternary Structure: Multiple polypeptide chains, e.g., hemoglobin, collagen.

• Protein Denaturation:

  • Changes in environment can affect structure; results in inactive proteins.

• Protein Folding:

  • Assisted by chaperonins; misfolding related to diseases like Alzheimer's.

Nucleic Acids

• Function:

  • Storage, transmission, and expression of hereditary information.

• Types of Nucleic Acids:

  • DNA (Deoxyribonucleic Acid):
    • Self-replicating; directs RNA synthesis.
  • RNA (Ribonucleic Acid):
    • Includes messenger RNA for protein synthesis.

• Components of Nucleic Acids:

  • Nucleotides:
    • Made of nitrogenous base, pentose sugar, and phosphate group.
  • Nitrogenous Bases:
    • Pyrimidines: Cytosine, Thymine (DNA), Uracil (RNA).
    • Purines: Adenine, Guanine.

• Structure of Nucleic Acids:

  • Backbone formed by sugar-phosphate linkages.
  • DNA Structure:
    • Double helix with antiparallel strands.
    • Complementary base pairing: A-T and G-C.
  • RNA Structure:
    • Usually single-stranded.
    • Transfer RNA has areas of base pairing.

• Genetic Information and Evolution:

  • DNA sequences passed from parent to offspring.
  • Genetic similarities indicate evolutionary relationships.