Biomolecules: Amino Acids
Reading: Ch. 2 (pg 60-61 & PANEL 2-5)

General Properties

  1. Common precursor biomolecule of all proteins
  2. Make up the proteins by assembling long chains of amino acids monomers
  3. 100's different types of amino acids, only 20 common in proteins
  4. 20 amino acids can make millions of different protein molecules
  5. To understand protein structure & function  must know properties different aa's. 

Structure of Amino Acids

  1. Each amino acid has an amino group and a carboxyl group, joined by a single Carbon atom (alpha carbon). 
  2. In addition, each aa has a characteristic "side chain" (called the -R group).
  3. View typical structure of an amino acid.
  4. Each amino acid (except glycine) can occur in two isomeric forms, L- and D-, because of the possibility of forming two different enantiomers (stereoisomers) around the central Carbon atom. Only L-amino acids are found in proteins in all organisms.
  5. View L- and D-valine
  6. Note: some D-amino acids are found in bacterial cell walls.
  7. "R" side groups can be any of 20 different groups of atoms.
  8. The most common amino acid, glycine, is only mildly nonpolar.
  9. Look at Panel 2-5 (pg 62-63) in text to see examples of all aa's.
  10. The great variety of side chains allows proteins to have many different (chemical) properties, and to create many different environments.

Peptide Bond and Dipeptides

  1. Amino acids are not accumulated by cells, but quickly joined into specific assemblies by the formation of peptide bonds .
  2. The peptide bond that binds amino acids is one of the strongest and most durable of covalent bonds. In the laboratory, we can break, or hydrolyze, peptide bonds most effectively by a combination of heat and acid. In your body, this digestive process begins in the stomach, where a combination of acid and enzymes help to break peptide bonds.If you didn't need to digest proteins, you wouldn't need a stomach!
  3. View formation of a peptide bond
  4. Two amino acids joined = dipeptide. Three AAs joined = tripeptide. 
    Many AAs joined = polypeptide .
  5. Students often confuse the term polypeptide with the term protein. " Polypeptide " refers to the structure of a single chain. Every polypeptide has one free amino group (called the "N-terminal") and one free carboxyl group (called the "C-terminal"). " Protein " refers to the overall functional assembly, created when one or more polypeptides fold up and become functional units. Some proteins consist of only a single folded polypeptide chain, but many proteins contain multiple polypeptides, and frequently inorganic atoms as well, such as Zn, Fe, Mg, etc.