Question

Which one of the following proteins would elute third in gel filtration chromatography from a mixture of four proteins given below?

• A. Insulin (6 kDa)
• B. Myoglobin (17 kDa)
• C. Thrombin (37 kDa)
• D. Albumin (66 kDa)

Hint:

Gel filtration elutes proteins largest first; rank the four molecular weights from biggest to smallest and count off the third one.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
Gel filtration (size exclusion) chromatography separates proteins purely by size, and the question gives four proteins of different molecular weights, asking which one comes out third.

Step 2: Key Formula or Approach:
In gel filtration, the column is packed with porous beads. Large proteins are too big to enter the pores, so they travel only through the spaces between the beads and come out first (in the void volume). Small proteins enter the pores, take a longer, winding path through the bead interiors, and come out last. So the elution order always runs from the largest protein first to the smallest protein last.

Step 3: Detailed Explanation:
Ranking the four proteins by molecular weight, largest to smallest:
Albumin, 66 kDa (largest)
Thrombin, 37 kDa
Myoglobin, 17 kDa
Insulin, 6 kDa (smallest)
Since the largest protein elutes first, the elution order is:
1st: Albumin (66 kDa)
2nd: Thrombin (37 kDa)
3rd: Myoglobin (17 kDa)
4th: Insulin (6 kDa)
So the protein eluting third is myoglobin.
Option (A), insulin, is the smallest protein, so it elutes last (fourth), not third.
Option (C), thrombin, is the second largest, so it elutes second, not third.
Option (D), albumin, is the largest protein, so it elutes first, not third.

Step 4: Final Answer:
Ranking the four proteins from largest to smallest gives the elution order albumin, thrombin, myoglobin, insulin, so myoglobin elutes third. \[ \boxed{\text{(B) Myoglobin (17 kDa)}} \]