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.