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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 p... 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 in proteins form between the electronegative oxygen of the carbonyl group (C=O) and the electropositive hydrogen of the amine group (N-H) in the polypeptide backbone. The slight positive charge on the hydrogen allows it to be attracted to the slightly negative oxygen of another amino acid, creating a stable hydrogen bond.
Step 2
Complete the structure to show the bond that forms between the side chains of two cysteine molecules.
Answer
The bond formed between two cysteine side chains is a disulfide bond (–S–S–). In the structure, each cysteine molecule's side chain will connect through the sulfur atoms:
R1 R2
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–CH–S—S–CH–
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H H
Step 3
Step 4
Draw the structure of the zwitterion of a dipeptide formed by alanine and serine.
Answer
The zwitterion structure of the dipeptide formed by alanine and serine is depicted as follows:
H O
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H2N–C–C–OH
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CH3 CH2
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H
In this representation, the amino group (–NH₃⁺) is positively charged, and the carboxyl group (–COO⁻) is negatively charged, making it a zwitterion.