State two functions of proteins, giving a named example of each.

Explain the significance of polar and non-polar amino acids.

enzymes/biological catalyst – amylase/protease/lipase/catalase;
defence/immunity – immunoglobin/antibody;
structure – collagen;
movement – actin/myosin;
transport – hemoglobin;
synthesis – ligase/DNA polymerase;
hormonal communication – insulin/luteinizing hormone; MUST be proteinaceous
food stores – casein in milk;
pigments – opsin;
Accept any other valid responses.

polar amino acids have hydrophilic R groups, non-polar have hydrophobic R groups;
non-polar amino acids in centre of water-soluble proteins stabilise their structure;
non-polar amino acids cause proteins to remain embedded in membrane;
polar amino acids on surface of proteins make them water-soluble;
polar amino acids create hydrophilic channels/protein pores in membranes;
enzyme active site specificity depends on amino acids present/polar and nonpolar amino acids can play a role in substrate interactions at the active site;

This was answered well by the majority of candidates, and they could give suitable named examples.

Many candidates gave vague responses, and many appeared to not understand the concept of hydrophilic and hydrophobic. Few could discuss the roles of the amino acids in proteins.