Identify the type of protein structure shown - AQA - A-Level Chemistry - Question 4 - 2022 - Paper 2
Question 4
Identify the type of protein structure shown.
Tick (✓) one box.
Primary
Secondary
Tertiary
Draw a structure for the –Cys–Ser– section of the protein.
Use the Da... show full transcript
Worked Solution & Example Answer:Identify the type of protein structure shown - AQA - A-Level Chemistry - Question 4 - 2022 - Paper 2
Step 1
Identify the type of protein structure shown.
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Answer
The protein structure depicted is classified as Primary. This is the sequence of amino acids in a polypeptide chain.
Step 2
Draw a structure for the –Cys–Ser– section of the protein.
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Answer
The structure can be depicted as follows:
H₂N H O
| | ||
C — C — C
| |
CH₂ OH
|
SH
This diagram shows the peptide link between the cysteine (Cys) and serine (Ser) amino acids.
Step 3
Name the other substance formed when two amino acids react together to form part of a protein chain.
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Answer
The other substance formed when two amino acids react together is Water (H₂O). This process is known as a condensation reaction.
Step 4
Explain why the strength of the interaction between two cysteine R groups differs from the strength of the interaction between a serine R group and an aspartic acid R group.
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The strength of interaction between two cysteine R groups is primarily due to the formation of disulfide bridges. These covalent bonds are stronger than hydrogen bonds, forming a strong link between cysteine residues.
In contrast, the interaction between a serine R group and an aspartic acid R group is mainly due to hydrogen bonding, which is weaker than disulfide bonds. Therefore, disulfide bridges contribute more significantly to the stability and strength of protein structure than hydrogen bonds.
Step 5
Deduce the type of interaction that occurs between a lysine R group and an aspartic acid R group.
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Answer
The interaction between a lysine R group and an aspartic acid R group is classified as an ionic bond. This occurs due to the positive charge on lysine interacting with the negative charge of aspartic acid.
