Question

you are working with a single polypeptide chain in the laboratory to determine what environmental factors affect its structure. at a ph of 7, the polypeptide has normal activity, but when you lower the ph to 5, you find that the polypeptide has no activity. returning the ph back to 7 restores the activity of the polypeptide. which statements likely explain the changes in protein activity observed in this scenario? select all that apply. changing the ph affected the secondary structure by changing hydrogen bonding between nearby amino acids. changing the ph affected the quaternary structure by breaking disulfide bonds. changing the ph affected the primary structure of the protein by breaking peptide bonds. changing the ph affected the tertiary structure by changing hydrogen bonding between distant amino acids.

Explanation:

1. Secondary structure: Hydrogen - bonding between nearby amino acids stabilizes secondary structure. Changing pH can disrupt these hydrogen bonds, altering secondary structure and thus protein activity.
2. Quaternary structure: This involves interactions between multiple polypeptide chains. Since we have a single polypeptide chain, quaternary structure is not relevant here.
3. Primary structure: Peptide bonds are not broken by pH changes in this context. They are stable under normal pH - changing conditions in the lab and are broken by proteases or extreme conditions like high heat and strong acids/bases.
4. Tertiary structure: Hydrogen - bonding between distant amino acids stabilizes tertiary structure. pH changes can disrupt these bonds, affecting the 3 - D shape and activity of the single polypeptide chain.

Answer:

Changing the pH affected the secondary structure by changing hydrogen bonding between nearby amino acids.
Changing the pH affected the tertiary structure by changing hydrogen bonding between distant amino acids.