Proteins

Question 1

Define the various classes of naturally occurring amino acids (7)

Answer 1

1) Aliphatic
2) Aromatic
3) Sulfur containing
4) Basic
5) Uncharged polar
6) Other (proline)

Question 2

Describe the functions of proteins (9)

Answer 2

• Proteins have a huge range of function in the body:
  1) Movement
  2) Protection
  3) Transport
  4) Enzymes
  5) Receptors
  6) Structural
  7) Storage
  8) Hormones
  9) Control of gene expression

Question 3

Define the primary structure of proteins

Answer 3

• Primary structure: The sequence of amino acids in a polypeptide chain. -> 20 possible occupants with enormous range of sequences theoretically possible, this is a source of versatility in protein structure and function.

Question 4

Define secondary structure of proteins

Answer 4

Secondary: The spatial arrangement of amino acids residues that are near each other in the linear sequence. Either in the form of an alpha helic or Beta pleated sheet. -> An alpha helic is in a telephone cord shape held in place by hydrogen bonds between every N-H group and the oxygen of the C=O group in the next turn of the helix.
Beta pleasted sheet structure is helf together by hydrogen bonds between the amide groups of linear polypeptide chains

Question 5

Define tertiary structure of proteins including the bonding

Answer 5

• Tertiary: The spatial arrangement of amino acid residues that are far apart in a linear sequence. They are held together by:
  1) Van der Waals – non-specific, weak attractions between atoms 0.3-0.4 nm apart – these are individually weak but in a folded protein structure a large number exist – thereby stabilizing the structure.
  2) Ionic interactions – occur between 2 close, op charged R groups.
  3) Hydrogen bonds – similar to van der waals but stronger and permanent (1/20 strength of a covalent bond though) occur when H is bonded to either O, N, or F and a lone pair of electrons are present.
  4) Disulphide bridges – strong covalent bonds between two cysteine residues, occur between as well as within polypeptides.
  5) Hydrophobic interactions –these are intra-polypeptide interactions which occur in an environment within proteins from which water is excluded.

Question 6

Define quaternary structure of proteins

Answer 6

• Quaternary: Refers to the spatial arrangement of individual polypeptide chains in a multi-subunit protein

Question 7

What is protein denaturation

Answer 7

Denaturation of proteins involves the disruption and possible destruction of both the secondary and tertiary structures.
Denaturation reactions are not strong enough to break the peptide bonds, so the primary structure remains the same after a denaturation process.

Question 8

6 causes of denaturation

Answer 8

1) Acids
2) Heat
3) solvents (ethanol, methanol)
4) Cross linking reagents (formaldehyde)
5) Chaotropic agents (urea)
6) Disulphide bond reducers (2 mercaptoethanol)

Question 9

What are 4 effects of denaturation

Answer 9

Decreased solubility
Altered water binding capacity
Loss of biological activity
Improved digestibility

Question 10

How can the peptide bonds and therefore the primary structure of a protein be disrupted?

Answer 10

Protein digestion by the action of enzymes