Basic Proteins Wk1

Question 1

What is the primary structure of proteins? (3)

Answer 1

• Individual sequence of amino acids held together by peptide bonds that determines the property of proteins
• R group will determine the polarity/water solubility of the molecules e.g. hydrophobic R group = tryptophan
• The charge of the R group contributes to the properties of the protein e.g. aromatic structure and aliphatic side groups

Question 2

What is the secondary structure of a protein? (2)

Answer 2

• Folding of the primary structure into chain coils of alpha helix or folds of a beta pleated sheet.
• Weak bonds between amino acids, but hydrogen bonds stabilise the structure.

Question 3

What is the tertiary structure of a protein? (2)

Answer 3

• Further folding of the polypeptide chain to give a more complex 3D structure closely related to the function of a particular protein.
• Proteins fold into a tertiary structure requiring the least amount of energy.

Question 4

What bonds hold the tertiary structure together? (4)

Answer 4

• Hydrogen bonds - weak bonds between R groups (easily broken)
• Ionic bonds between positively and negatively charged R groups of amino acids
• Disulphide bonds - strong covalent bonds formed between sulphurs in the R group of the amino acid C(ysteine)
• Hydrophobic interactions between non-polar R groups which tend to cluster together towards centre of molecule.

Question 5

What is a quaternary protein structure? (1)

Answer 5

A complex of more than one polypeptide chain (e.g. haemoglobin contains 4 polypeptide chains, 2 alpha and 2 beta)..

Question 6

What are globular proteins? (4)

Answer 6

• Tertiary structure
• For secretion from the cell - more water soluble than fibrous
• Small, condense, early transported, fold up into a compact ball like shape (hydrophobic R groups facing inwards and vice versa)
• E.g. enzymes (metabolic role)

Question 7

What are fibrous proteins? (3)

Answer 7

• Tertiary structure
• Long fibres formed of regular, repetitive sequences and usually insoluble in water
• Elongated for strength

Question 8

How is structure determined? (2)

Answer 8

• X-ray crystallography

- NMR