Question

The largest known protein is

• A. Collagen
• B. Keratin
• C. Titin
• D. Myosin

Hint:

Titin's massive size is encoded by a single gene containing 363 exons, which is the largest number of exons found in any single gene.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Proteins vary widely in molecular weight and polypeptide chain length, ranging from small peptide hormones to massive structural macromolecules.

Step 2: Detailed Explanation:
The largest known single polypeptide chain is Titin (also known as connectin).
Titin is a giant filamentous structural protein expressed in cardiac and skeletal muscle fibers.
In humans, a single titin molecule contains up to 34,350 amino acids, with a molecular mass of approximately 3 to 4 million Daltons (3,000–4,000 kDa).
It spans half the sarcomere length, from the Z-disc to the M-line, acting as a molecular spring that maintains the structural alignment of thick filaments (myosin) during muscle contraction and relaxation.
In contrast, other structural proteins like collagen, keratin, and myosin are significantly smaller:
- Myosin heavy chains are approximately 220 kDa.
- Individual collagen chains are approximately 100 kDa.
Thus, Titin is the largest known protein.

Step 3: Final Answer:
The largest known protein is Titin.