IB Biology HL - Proteins (B1.2) Vocabulary

Protein Elements and Monomers

  • Elements: C, H, O, N, sometimes S.
  • Monomers: Amino acids (20 different types).
  • Amino Acid Structure:
    • Amine group (-NH₂): Basic.
    • Carboxyl group (-COOH): Acidic.
    • Alpha carbon (Cα): Central carbon.
    • R group (side chain): Determines properties.

Condensation Reactions and Peptide Bonds

  • Condensation Reaction: Forms water and a peptide bond.
  • Location: Ribosomes.
  • Dipeptide: 2 amino acids.
  • Oligopeptide: 3-20 amino acids.
  • Polypeptide: More than 20 amino acids.

Variety of Proteins

  • Amino acid sequence determined by DNA base sequence.
  • 4^n possible combinations of sequences, where n is the length of the gene.
  • A protein with only 10 amino acids would be 20^{10}, leading to 10,240,000,000,000 possible combinations!
  • R-groups: Hydrophilic (exterior) or hydrophobic (interior).
  • R-group interactions determine protein shape and function.

Protein Conformation

  • Primary Structure: Amino acid sequence.
  • Secondary Structure: Hydrogen bonds form alpha-helices or beta-pleated sheets.
  • Tertiary Structure: Hydrogen bonds, ionic bonds, disulfide bonds (cysteine), hydrophobic interactions.
  • Quaternary Structure: Multiple subunits or conjugated with a prosthetic group.

Globular vs. Fibrous Proteins

  • Globular Proteins: Soluble, compact, functional (e.g., insulin).
  • Fibrous Proteins: Insoluble, long, structural (e.g., collagen).

Denaturation of Proteins

  • Cause: pH changes or temperature increase breaks bonds.
  • Effect: Loss of shape and function.
  • Irreversible: Typically irreversible.

Effect of Temperature and pH

  • Optimal Temperature: Proteins function best (e.g., 37°C for human proteins).
  • Optimal pH: Varies for different proteins (e.g., pepsin at pH 1.5-1.6, trypsin at pH 7.8-8.7).
  • Denaturation: Occurs above or below optimal conditions.

Technology and Imaging (Cryo-EM)

  • Flash-freezes molecules to preserve natural structure.
  • Electrons are transmitted through the molecule to produce an image.
  • Multiple images are compiled to create a 3D, high-resolution image.

Dietary Requirements of Amino Acids

  • Plants: Synthesize all 20 amino acids.
  • Animals: Synthesize 11 nonessential amino acids.
  • Essential Amino Acids: 9 amino acids obtained through diet.
  • Complete Protein: Contains all 9 essential amino acids (e.g., meat, soy, quinoa).
  • Incomplete Protein: Lacks one or more essential amino acids (e.g., beans, nuts).
  • Vegetarian/Vegan Diet: Must combine plant-based proteins.