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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

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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.

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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.

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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 
   |    | 
–CH–S—S–CH–
   |    |
  H   H 

Step 3

Name this type of protein structure.

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Answer

This type of protein structure is known as tertiary structure.

Step 4

Draw the structure of the zwitterion of a dipeptide formed by alanine and serine.

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Answer

The zwitterion structure of the dipeptide formed by alanine and serine is depicted as follows:

  H   O 
  |   ||
H2N–C–C–OH 
  |   |  
 CH3  CH2 
         | 
        H  

In this representation, the amino group (–NH₃⁺) is positively charged, and the carboxyl group (–COO⁻) is negatively charged, making it a zwitterion.

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