2.3.1

Amino Acids & Overview of Protein Structure

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Polypeptides

Amino acids are the monomers that join together to form polymers called polypeptides (proteins).

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Structure of proteins

  • Proteins are made up of amino acids.
  • Dipeptides are formed from the condensation of two amino acids.
  • Polypeptides are formed by the condensation of many amino acids.
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Structure of amino acids

  • Each amino acid has a central carbon atom (alpha carbon).
  • There are four atoms or groups of atoms bonded to the central carbon atom:
    • NH2 (an amino group).
    • COOH (a carboxyl group).
    • H (a hydrogen atom).
    • R (a side group).
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R groups

  • The R group is different in each amino acid.
  • The R group determines how the amino acid interacts and bonds with other amino acids in the polypeptide.
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Essential amino acids

  • There are 20 different types of amino acids that are common in all organisms.
    • 9 of these are essential amino acids in humans because the human body cannot produce them and they are obtained from the diet.
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Glycine

  • Glycine is an example of an amino acid.
  • Glycine has a hydrogen atom in its R group.
  • Glycine is the only amino acid that does NOT have a carbon atom in its R group.

Peptide Bond

Each amino acid is attached to another amino acid as a result of a condensation reaction. These reactions cause peptide bonds to form.

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Polypeptides

  • Polypeptides are made from chains of amino acids.
  • There are amino acids at each end of the polypeptide chain.
  • These amino acids form the two end terminals:
    • The N-terminal (amine terminal).
    • The C-terminal (carboxyl terminal).
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The peptide bond

  • When two amino acids react together, a bond forms between the carboxyl group of one amino acid and the amino group of a second amino acid.
  • One water molecule is released as a by-product.
  • The bond formed between two amino acids is a covalent bond called a peptide bond.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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