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Proteins are polymers made from amino acids - AQA - A-Level Chemistry - Question 4 - 2022 - Paper 2
Question 4
Proteins are polymers made from amino acids. Part of the structure of a protein is shown. --Cys--Ser--Asp--Phe-- Each amino acid in the protein is shown using the ... show full transcript
Worked Solution & Example Answer:Proteins are polymers made from amino acids - AQA - A-Level Chemistry - Question 4 - 2022 - Paper 2
Step 1
Step 2
2. Draw a structure for the--Cys--Ser-- section of the protein.
Answer
The structure for the --Cys--Ser-- section of the protein can be represented as:
H₂N--C--COOH
|
R
Cys: -CH₂-SH
H₂N--C--COOH
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R
Ser: -CH₂-OH
Including the peptide bond:
H₂N--C--COOH H₂N--C--COOH
| | |
R H₂O R
This shows the connection through a peptide bond linking cysteine and serine.
Step 3
Step 4
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.
Answer
The strength of the interaction between two cysteine R groups is stronger due to the formation of disulfide bridges, which are covalent bonds that occur between the sulfur atoms of two cysteine residues. In contrast, the interaction between a serine R group and an aspartic acid R group primarily involves hydrogen bonds, which are generally weaker than disulfide bonds. Disulfide bridges provide greater stability to protein structure due to their covalent nature, while hydrogen bonds are more transient.
Step 5
5. Deduce the type of interaction that occurs between a lysine R group and an aspartic acid R group.
Answer
The type of interaction that occurs between a lysine R group and an aspartic acid R group is an ionic bond. Lysine has a positively charged amino group in its side chain, while aspartic acid has a negatively charged carboxyl group, allowing for electrostatic attraction between these two oppositely charged R groups.