Amino acids are the monomers that are used to produce proteins in organisms. Amino acids also have other, non-protein, roles in the body. Fig. 7.1 shows the structures of five amino acids with varying numbers and arrangements of carbon atoms. [Figure 7.1]

1. (a)In the liver, one of these amino acids can be converted to pyruvate and one of these amino acids can be converted to oxaloacetate. Suggest which of the amino acids shown in Fig. 7.1 would be most directly converted to: • pyruvate • oxaloacetate. amino acid converted to pyruvate amino acid converted to oxaloacetate[2]
2. (b)(i)The amino acid glycine can act as a neurotransmitter. A glycinergic synapse is shown in Fig. 7.2. The glycinergic synapse and a cholinergic synapse use different neurotransmitters and different postsynaptic receptors. Describe differences between the glycinergic synapse shown in Fig. 7.2 and a cholinergic synapse.[2]
3. (b)(ii)The binding of glycine to receptors, as shown in Fig. 7.2, makes an action potential less likely to occur in the postsynaptic neurone. Suggest why an action potential is less likely to occur after the binding of glycine to receptors.[2]
4. (b)(iii)Neurones need to maintain a resting potential before an action potential can occur. Describe how a neurone maintains a resting potential.[4]

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