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Contents 1 Explain the Four levels of structure of proteins and their significance 2 Outline the difference between Fibrous and Globular proteins 3 Explain the significance of Polar / Non Polar Amino Acids 4 State Six functions of Proteins, giving an example of each 5 Comments

Explain the Four levels of structure of proteins and their significance

• Primary
  • Nature
    • Linear sequence of amino acids with peptide linkages
  • Significance
    • Changes in sequence may have overall effect on structure and activity
    • Almost infinite number of sequences
• Secondary
  • Nature
    • The formation of the alpha-helix and beta-pleated sheets, held together by hydrogen bonds.
  • Significance
    • ?
• Tertiary
  • Nature
    • a complex structure, usually globular, resulting from further folding of the secondary structure of protein
    • forms spontaneously due to attractions and repulsions among amino acids with different charges on their R groups
    • Active sites possible,added strength due to Ionic bonds, disulphide linkages, and possibly prosthetic groups and coenzymes.
• Quaternary
  • the overall structure of a globular protein molecule that consists of two or more polypeptide chains.
  • Most large, non-structural proteins have more than one polypeptide and this leads to a greater range of biological activity.

Outline the difference between Fibrous and Globular proteins

Outline the difference between Fibrous and Globular proteins, with reference to two examples of each type

	Fibrous Proteins	Globular Proteins
Sequences of amino acids	Regular	Irregular
Polypeptide Chains	Long Parallel Strands	Folded Into Spherical Shape
Length of Chain	Varies	Identical
Structure	Stable	Instable
Solubility	Insoluble	Soluble
Function	Structural	Metabolic
Examples	Collagen and keratin	Enzymes and hormones insulin and haemoglobin

Explain the significance of Polar / Non Polar Amino Acids

• There are only 20 different amino acids, and the only differences between them lie in their side (-R) groups.
• The side groups in seven of the amino acids have Polar Regions; in acid or basic solution, these regions can become charged.
• In eight of the molecules, the side group consists of short chains or rings of carbon and hydrogen atoms as you would expect, such groups are non-polar and thus hydrophobic.
• The remaining five amino acids have side groups that are either weak acids or weak bases.

State Six functions of Proteins, giving an example of each

• Enzymes - pepsin
• Cell transport - membrane proteins
• Structural - collagen
• Hormones -insulin
• Immunoglobulins - antibodies
• Transport - haemoglobin

Comments