A diploid organism has 4.5 x 108 base pairs(bp) in its DNA. a. If the organism h

Question

A diploid organism has 4.5 x 108 base pairs(bp) in its DNA.

a. If the organism has a diploid number of 6, what is the average number of base pairs in a chromosome of this organism?

b. How long would the the DNA molecule be in micrometers?

c. In the S phase of this organism’s cell cycle the cell’s DNA is completely replicated in 3 minutes. Assuming all replication forks move at a rate of 1 x 104 bp per minute how many origins of replication are present in the organism’s genome? Assume bidirectional replication. You must explain your answer carefully!

Explanation / Answer

A) We know, number of base pairs = 4.5 x 10^8

Also, 2n =6

Therefore, if we assume that bases are equally distributed on all chromosomes,

Total base pairs/6 = (4.5 x 10^8)/6 = 7.5 x 10^7 base pairs per chromosome.

B) Distance between two base pairs is 3.4 Angstorm

Length of DNA = (Number of base pairs - 1) x 3.4 Angstorm

= [(4.5x10^8)-1] x 3.4 = 15.3 x 10^8 Angstorm

= 153000 micrometer

C) We know, rate of replication per fork = 104 base pair per minute.

Now, 4.5 x 10^8 bases need to be replicated.

In one minute,( 4.5 x 10^8 ) / 3 = 1.5 x 10^8

Now, rate per fork is 10^4 base pairs per minute

Therefore, number of forks = 1.5 x 10^8/10^4 = 1.5 x 10^4 = 15,000 origin of replication present.

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