(a)     List four major functions of proteins in the human body.

(b)     Deduce the structures of two different tripeptides that can be formed when all three amino acids given below react together.

(c)     Deduce the number of tripeptides that could be formed by using all three of the above amino acids to form a tripeptide.

(d)     State the type of bonding that is responsible for the primary and secondary structures of proteins.

Primary:

Secondary:

(e)     Describe and explain the tertiary structure of proteins. Include in your answer all the bonds and interactions responsible for the tertiary structure.

(a)     structure / growth / repair

enzymes

hormones

transport

immunoproteins/antibodies

energy source

Two functions score [1].

(b)     

Accept CONH for peptide bond.

Penalize incorrect representation of peptide bond (e.g. COHN) once only.

(c)     6;

(d)     

(e)     secondary structure folds to form a (unique) 3-D/dimensional structure of the protein;

Structure stabilized by:

covalent bonds / disulfide bridges

hydrogen/H-bonding

ionic bonds / salt bridges

van der Waals’/dispersion/London forces

Two bond types score [1].

Often quite well done. In part (a), whilst proteins can be used as an energy source, energy storage would not be considered a major function as the body usually stores energy in other forms. In Part (e), few candidates pointed out that the tertiary structure is a folding of the primary and secondary structures that gives the protein its three-dimensional shape.