Proteins

• What is the main difference between triglycerides and phospholipids?


  Phospholipids contain one phosphate group replacing a fatty acid.
• What does a phospholipid contain that a triglyceride does not?


  One phosphate group.
• What distinguishes saturated fats from unsaturated fats?


  Saturated fats have all carbon valencies filled with hydrogen and no double bonds.
• What type of bonds do saturated fats have between carbon atoms?


  Single bonds.
• What type of bonds do unsaturated fats contain?


  Double bonds.
• What are the functions of proteins?

  • Enzymes (e.g., Amylase)
  • Transport (e.g., Haemoglobin)
  • Movement (e.g., Actin & Myosin)
  • Cell recognition (e.g., Antigens)
  • Channels (e.g., Membrane proteins)
  • Structure (e.g., Collagen & Keratin)
  • Hormones (e.g., Insulin)
  • Protection (e.g., Antibodies)
• What elements are proteins made from?


  Carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.
• What determines the properties of a protein?

  The sequence of amino acids.
• How many amino acids are there approximately?


  About 20 amino acids.
• What is the R-group in an amino acid?


  The side chain that differs among amino acids.
• How many possible combinations of amino acids are there in a polypeptide with 3 amino acids?


  There are 8000 combinations.
• What is the primary structure of a protein?


  The linear sequence of amino acids.
• What is the secondary structure of a protein?


  The repeating pattern in the structure of peptide chains, such as alpha helices or beta pleated sheets.
• What is the tertiary structure of a protein?


  The 3D folding of the protein due to bonding between R-groups.
• What is the quaternary structure of a protein?


  The 3D arrangement of more than one tertiary protein.
• What bond is formed between two monosaccharides?

  Glycosidic bond.
• How do you test for lipids?


  Mix with ethanol, add water, and observe for a milky white emulsion.
• What bond is formed between glycerol and three fatty acids to form a triglyceride?


  Ester bond.
• What type of reaction forms a polypeptide from amino acids?


  Condensation reaction.
• Describe the primary, secondary, and tertiary structures of a polypeptide.


  1. Primary: Linear sequence of amino acids (polypeptide chain).
  2. Secondary: Hydrogen bonds form between -COOH and -NH2, resulting in alpha helices or beta pleated sheets.
  3. Tertiary: 3D shape formed by bonding between R-groups, held together by hydrogen bonds, ionic bonds, and disulphide bridges.
• What is the Biuret test used for?


  To test for the presence of proteins.
• What is a positive result for the Biuret test?


  The solution turns lilac.
• Describe the biochemical tests for lipid, non-reducing sugar, and protein.


  • Lipid: Add ethanol, then water; positive result is a white/milky emulsion.
  • Non-reducing sugar: Benedict's test stays blue; boil with acid, neutralize, then heat with Benedict's; positive result is red/orange precipitate.
  • Protein: Add Biuret reagent; positive result is purple/violet/lilac.
• Describe the structure of an amino acid molecule and how amino acids link together.

  1. Amino acid based on carbon with four groups attached.
  2. Amino group (NH2) and carboxyl group (COOH).
  3. R-group/side chain + hydrogen.
  4. R-group differs among amino acids.
  5. Amino acids joined by condensation.
  6. Bond formed between NH2 and COOH.
  7. Involves removal of a molecule of water (H from NH2 and OH from COOH).
• How is the primary, secondary, and tertiary structure of a polypeptide produced by bonds between amino acids?


  1. Peptide bonds form between adjacent amino acids creating a polypeptide chain.
  2. The chain twists into an alpha helix or folds into a beta pleated sheet (secondary structure).
  3. Held together by hydrogen bonds between amino acids.
  4. The molecule folds into a 3D shape (tertiary structure).
  5. Held together by hydrogen bonds, ionic bonds, and disulphide bridges.