2.3.2

Primary & Secondary Structure

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Primary Structure of Proteins

The order of amino acids in a polypeptide determines the primary structure of a protein.

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Amino acid sequence

  • Amino acids in a polypeptide chain are arranged in a specific sequence.
  • The sequence of amino acids is the primary structure.
  • The primary structure is determined by the gene encoding the protein.
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Importance

  • A change in the nucleotide sequence of the gene's coding region may lead to a different amino acid being added to the growing polypeptide chain.
  • A change in the amino acids in a protein could change the protein's structure and function.

Secondary Structure of Proteins

The primary polypeptide chain folds to form a secondary structure.

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Hydrogen bonds

  • Amino acids in a polypeptide chain can form hydrogen bonds between other amino acids within the chain.
  • The hydrogen bonds cause the protein to fold into specific structures.
  • Folding of the polypeptide determines its secondary structure.
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Common structures

  • The most common secondary structures are the alpha-helix and beta-pleated sheet structures.
    • E.g. Silk has a β-pleated sheet structure.

Stability

  • The secondary structure of a protein is stable.
  • Individual hydrogen bonds are quite weak, but there are many bonds throughout the molecule which leads to overall high stability.
  • The stability of the secondary structure is decreased by environmental factors that weaken the hydrogen bonds (e.g. temperature, pH).

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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