1. There was a 5952 bp long gene in one of the region of a dsDNA of a cell. The
ID: 281508 • Letter: 1
Question
1. There was a 5952 bp long gene in one of the region of a dsDNA of a cell. The length of the RNA primer was 8 bp. The gene takes 119 seconds for complete replication (a) Calculate the speed of the replication machine. (1 mark) (b) After 32 rounds of replication the size of the gene was found to be less than 744 bp. It means some regions of the DNA has been lost. Critically analyze this situation and develop a logical reason for this phenomenon. If the same phenomenon continues, what will happen to the gene? (1 mark] 2. A Young group of interstellar voyagers from MIT, Manipal returned earth on April 20, 3015. They came with an alien DNA sample consisting of 5 X 1010 bp. They also found this much of DNA was organized into 10 different pieces (chromosomes) as even distribution. (a) A group calculates the speed of the replication machine as 2 X 104 bp per minute for both strands. Then how long it will take to complete one cycle of replication? (1 Mark) (b) A curious student sticks this 10 different pieces and wanted measure its length. According to you what would be the length now? Express in meters. (1 Mark)Explanation / Answer
Answer 1a) Speed of replication machine = 5952 base pairs/119 seconds = 50.02 base pairs/sec or 3000 bp per minute.
Answer 1b) After 32 rounds, the gene was having 744 base pairs which surely mean some parts are lost.
This occurs because in replication of lagging strand (formed by Okazaki fragments), number of RNA primers are attached, when these primers are removed, some of the base pairs are lost, specifically of the last RNA primer. This process is named as telomere shortening as this occurs in the telomeric part of chromosomes.
The gene may totally loose its information if the process is continued but in some actual living cells the enzyme named as telomerase is present which prevent telomere shortening and adds the base pairs.
Answer 2a) One replication cycle stands for complete replication of whole genetic material once. i.e. if dsDNA molecule consists of 50 bp, after one replication cycle there will be two dsDNA molecules (daughter DNA) of 50 bp each and these will be hybrid i.e one of the strand would be from template DNA and another would be new in each daughter.
Now, speed of replication machine = 2 x 104 bp/minute
Total DNA = 5 x 1010 bp
Total time taken = total DNA/speed of replication machine = 5 x 1010/2 x 104 = 2.5 x 106 minutes.
Answer 2b) Length of one base pair = 340 picometer (approx.) or 340 x 10-12 meters.
Now total base pairs are 5 x 1010
So total length = No. of base pairs x length of one base pair
total length = (5 x 1010) x (340 x 10-12) = 1700 x 10-2 meters or 17 meters.
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