List three functions of proteins, giving a named example of each.

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

catalysts/digestion – amylase/protease/lipase/catalase;
defense – immunoglobin / fibrinogen;
structure – collagen;
movement – actin/myosin;
transport – hemoglobin;
synthesis – ligase/DNA polymerase;
hormonal communication – insulin/luteinizing hormone;
light detection – rhodopsin / plant phytochromes;
storage – ferritin/gluten/casein;
Accept any other valid responses.

non-polar amino acids for hydrophobic part of the bilipid layer;
polar amino acids for hydrophilic environment;
polar amino acids allow hydrophilic channels;
integral proteins are held in place by polar amino acids;
To award [2 max] both polar and non-polar should be addressed.
Accept answers in the form of a diagram.

Here some candidates did not read the entire question and only listed the functions without a named example.

C3 (b) seemed to be very difficult and very few got this question right. Some candidates did mention the polarity and hydrophobicity of the amino acids, but did not mention the significance of them to membranes. This is clearly an area that needs reinforcing.