During translation, a polypeptide is synthesised when amino acids are added to a growing chain of amino acids. Fig. 1.1 shows part of a growing chain of amino acids and the amino acid cysteine. [Figure 1.1] Fig. 1.2 is a ribbon diagram showing the three-dimensional structure of a protein from the bacterium Streptococcus. [Figure 1.2]

1. (a)(i)Complete Fig. 1.1 by showing the formation of the bond between cysteine and the growing chain of amino acids in the process of translation.[3]
2. (a)(ii)State the name of the covalent bond that forms when cysteine is added to the growing chain of amino acids.[1]
3. (a)(iii)State the organelle where the reaction shown in Fig. 1.1 takes place.[1]
4. (b)(i)Describe the secondary structure of the protein shown in Fig. 1.2.[2]
5. (b)(ii)Explain why the protein shown in Fig. 1.2 has tertiary structure, but not quaternary structure.[2]
6. (b)(iii)An analysis of the amino acid composition of the protein in Fig. 1.2 showed that it does not contain any cysteine residues. Explain how the three-dimensional structure of the protein shown in Fig. 1.2 is held in place.[3]

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