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The structure of a section of a protein chain is shown in the diagram below: ---N---C---C---N---C---C---N---C---C--- | | | | | | | | | H O H H O H H O H H O H II | II | II | C---C---C----C----C----C OH----- | H | H | | H---C---C---C---C H | | | H CH2 CH3 | \ CH3 In water, protein molecules often adopt a roughly spherical tertiary structure in which the side chain groups play an important role in influencing shape and solubility - VCE - SSCE Chemistry - Question 8 - 2006 - Paper 1
Question 8
The structure of a section of a protein chain is shown in the diagram below: ---N---C---C---N---C---C---N---C---C--- | | | | | | | | | ... show full transcript
Worked Solution & Example Answer:The structure of a section of a protein chain is shown in the diagram below: ---N---C---C---N---C---C---N---C---C--- | | | | | | | | | H O H H O H H O H H O H II | II | II | C---C---C----C----C----C OH----- | H | H | | H---C---C---C---C H | | | H CH2 CH3 | \ CH3 In water, protein molecules often adopt a roughly spherical tertiary structure in which the side chain groups play an important role in influencing shape and solubility - VCE - SSCE Chemistry - Question 8 - 2006 - Paper 1
Step 1
i. On the above structure of the protein chain, circle the side chain group that is hydrophobic.
Answer
In the provided structure, the hydrophobic side chain group consists of the hydrocarbon tails, which should be circled. This group does not interact favorably with water, making it hydrophobic.
Step 2
ii. In general, would you expect hydrophobic groups to be in the interior or to be on the external surface of water soluble proteins? Explain your reasoning.
Answer
Hydrophobic groups are expected to be in the interior of water-soluble proteins. This is because these groups do not interact favorably with water and tend to cluster together, away from the aqueous environment, to minimize exposure to water, thus stabilizing the protein's structure.
Step 3
i. When this section of the protein is hydrolysed, one of the amino acids formed has a carbon to nitrogen ratio of 3:1.
Answer
An amino acid with a carbon to nitrogen ratio of 3:1 can be represented as follows:
H O
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H--N---C---C---C---OH
| | |
H H H
This represents an amino acid with three carbon atoms and one nitrogen atom.
Step 4
ii. In box B below, draw the structural formula of this same amino acid as it would most likely exist at pH 2.
Answer
At pH 2, the amino acid would be protonated. Its structure can be drawn as:
H O
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H--N^+--C---C---C---OH
| | |
H H H
The amino group is protonated ( N^+ ) and the carboxylic acid group remains as an acid at this pH.
Step 5
Explain the chemical basis of this observation.
Answer
The browning reaction is due to the oxidation of phenolic compounds facilitated by polyphenol oxidase. Boiling the vegetables denatures the enzyme, stopping the browning reaction. Upon cooling, the denatured enzyme does not react with oxygen, thus preventing browning.
Step 6