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Q: G17 and G34 is derived from a polypeptide precursor of 104 amino acids. The functional difference between G17 and G34 is attributable to differences in their:
A. primary structures.
A is the best answer. In order to understand a protein's structure and its mechanism of action, a knowledge of the primary structure is needed. In fact, the data most often used to predict the similarity between two or more proteins are their the primary structures. Regular secondary structures in proteins include the α-helix and β-sheet. The relationship between these primary and secondary structures in three-dimensional space gives the protein its tertiary structure. Quaternary structure refers to the conformation of a multichained polypeptide. Since gastrin is derived from a single polypeptide chain of 104 amino acids, it would not have quaternary structure. Proteolytic removal of the N-terminal amino acid residues from G34 gives G17. The two polypeptides (G17 and G34) share a common C-terminal region. Because of this, we would expect their secondary and tertiary structures to be similar. What is different between G17 and G34 is the amino acids removed at the N-terminal end. In other words, the primary structure of gastrin has been changed in going from G34 to G17. This is reflected in its activity. As was mentioned in the passage, G17 is about five times more active than G34. The best answer is A.
I chose tertiary structures, since it's the shape of the protein that determines its structure. I understand that tertiary structure is derived from primary structure, but when the question is asking about FUNCTIONAL difference, wouldn't that be more affected by tertiary structure? If the question said something about being "ultimately attributable to" or something along those lines, I'd understand the answer being primary structure, but that wasn't the case. Any help would be appreciated!
A. primary structures.
A is the best answer. In order to understand a protein's structure and its mechanism of action, a knowledge of the primary structure is needed. In fact, the data most often used to predict the similarity between two or more proteins are their the primary structures. Regular secondary structures in proteins include the α-helix and β-sheet. The relationship between these primary and secondary structures in three-dimensional space gives the protein its tertiary structure. Quaternary structure refers to the conformation of a multichained polypeptide. Since gastrin is derived from a single polypeptide chain of 104 amino acids, it would not have quaternary structure. Proteolytic removal of the N-terminal amino acid residues from G34 gives G17. The two polypeptides (G17 and G34) share a common C-terminal region. Because of this, we would expect their secondary and tertiary structures to be similar. What is different between G17 and G34 is the amino acids removed at the N-terminal end. In other words, the primary structure of gastrin has been changed in going from G34 to G17. This is reflected in its activity. As was mentioned in the passage, G17 is about five times more active than G34. The best answer is A.
I chose tertiary structures, since it's the shape of the protein that determines its structure. I understand that tertiary structure is derived from primary structure, but when the question is asking about FUNCTIONAL difference, wouldn't that be more affected by tertiary structure? If the question said something about being "ultimately attributable to" or something along those lines, I'd understand the answer being primary structure, but that wasn't the case. Any help would be appreciated!
