MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A biochemist is synthesizing a polypeptide chain in vitro. They notice that the addition of a specific molecule causes the nascent polypeptide to fold into an incorrect, non-functional conformation. This molecule likely interferes with which level of protein structure?
- ATertiary structure
- BQuaternary structure
- CSecondary structure
- DPrimary structure
Show answer & explanationAnswer & explanation
Correct answer: A. Tertiary structure
The tertiary structure refers to the overall three-dimensional folding of a single polypeptide chain, which determines its functional conformation. Interference leading to incorrect folding most directly affects this level.
Why the other options are wrong
- B. Quaternary structure involves the arrangement of multiple polypeptide subunits; this question describes a single nascent polypeptide.
- C. Secondary structure involves local folding patterns like alpha-helices and beta-sheets, which are components of the overall 3D fold, but incorrect overall folding points to tertiary structure.
- D. Primary structure is the amino acid sequence; incorrect folding doesn't change the sequence itself.
Tertiary Protein Structure
The overall three-dimensional shape of a single polypeptide chain, resulting from interactions between the side chains of amino acids.
- Determines the protein's specific function.
- Involves various bonds: hydrogen, ionic, disulfide, hydrophobic interactions.
- Incorrect folding leads to loss of function.
Memory trick: Primary's sequence, Secondary's folds, Tertiary's 3D, Quaternary's groups.