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Use the Data Booklet to help you answer this question about amino acids - AQA - A-Level Chemistry - Question 8 - 2018 - Paper 2
Question 8
Use the Data Booklet to help you answer this question about amino acids. Figure 1 shows parts of two polypeptide chains in a beta-pleated sheet of a protein. The ... show full transcript
Worked Solution & Example Answer:Use the Data Booklet to help you answer this question about amino acids - AQA - A-Level Chemistry - Question 8 - 2018 - Paper 2
Step 1
Explain how these hydrogen bonds form.
Answer
Hydrogen bonds form between the electronegative atom, usually oxygen, and a hydrogen atom that is covalently bonded to another electronegative atom. In the context of polypeptide chains, when the carbonyl (C=O) group of one amino acid aligns with the amine (N-H) group of another amino acid, the hydrogen atom bonded to nitrogen is attracted to the oxygen of the carbonyl group. This creates a weak electrostatic attraction, stabilizing the structure of the protein.
Step 2
Complete the structure to show the bond that forms between the side chains of two cysteine molecules.
Answer
The bond that forms between the side chains of two cysteine molecules is a disulfide bond (—S—S—). This occurs through the oxidation of the thiol (—SH) groups present in the cysteine residues.
Step 3
Step 4
Draw the structure of the zwitterion of a dipeptide formed by alanine and serine.
Answer
The zwitterion structure of a dipeptide formed by alanine (H2N-CH(CH3)-COOH) and serine (H2N-CH(CH2OH)-COOH) can be represented as follows:
H O
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H2N-CH-COOH H2N-CH-COOH
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CH3 CH2OH
In the zwitterion form, the amino group is positively charged and the carboxyl group is negatively charged, leading to a neutral overall charge.