Question

Without histones, unwound DNA in chromosomes would be very long and the length of completely stretched DNA within each human cell would be:

• A. 1.0 meters
• B. 1.5 meters
• C. 1.8 meters
• D. 2.5 meters

Hint:

Total DNA length in human cell: ~1.8 meters.
Compacted with histones into chromosomes.
Packaging ratio is about 10,000:1.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
DNA is highly compacted in the nucleus by histones.
Without histones, DNA would be very long.

Step 2: Key Formula or Approach:
No specific formula.
Need to know the total length of DNA in a human cell.

Step 3: Detailed Explanation:
The human genome has approximately 3.3 billion base pairs.
Each base pair is about 0.34 nm long.
Total length = 3.3 \(\times\) 10\(^9\) \(\times\) 0.34 nm = 1.12 \(\times\) 10\(^9\) nm = 1.12 m.
However, considering that each cell has two copies of each chromosome (diploid),
the total length would be about 2.0 m.
The commonly cited value is approximately 1.8 meters.
Thus, the length of completely stretched DNA is about 1.8 meters.

Step 4: Final Answer:
The length of completely stretched DNA in each human cell is 1.8 meters.
Hence, the correct option is (C).