Question

Each human cell normally contains 23 pairs of chromosomes. Chromosome 1 is the longest and is approximately 247,200,000 basepairs in length.

(A) If there was only one origin of replication, how long (in hours) would it take to replicate Chromosome 1? Remember, the replication rate in eukaryotes is ~75 nucleotides/second.

(B) It actually takes 8 hours to replicate Chromosome 1. How many evenly spaced origins of replication would be needed to realize this rate of replication?

(C) Considering all 23 chromosomes, the human genome is approximately 3,200,000,000 basepairs in length. If the genome was one continuous strand of duplex DNA, how long would that piece of DNA be (in meters). Assume that there are 10.4 basepairs per helical turn, and the pitch of one turn of the helix is 35.4 Å. Remember, 1Å = 10^–10 m.

Answer 1

A) Given, length of chromosome 1 = 247,200,000 base pairs, replication rate = ~75 nucleotides/second

So, required time = (247,200,000/75) seconds = 3,296,000 seconds = (3,296,000/3600) hours (As 1 hour = 3600 seconds) = 915.56 hours (Up to 2 decimals)

B) Given, actual time = 8 hours

So, required number of origins of replication = 915.56/8 = 114.445 114

C) Given, size of human genome = ~3,200,000,000 base pairs, number of base pairs per helical turn = 10.4, pitch of one turn of the helix = 35.4 Å

So, numbers of helical turn = 3,200,000,000/10.4

So, length of DNA strand = [(3,200,000,000/10.4) x 35.4] Å

So, length of DNA strand (in meter) = [(3,200,000,000/10.4) x 35.4 x 10-10] m = 1.089 m (Up to 3 decimals)