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Question 1 (0.5 points) Why is there a lagging strand and a leading strand during replication? O Because the helicase unwinds the dna in only one direction. Because DNA polymerase can only add nucleotides to the 3'end of a chain of nucleotides and replication proceeds in both directions. b) c) Because a primer must be laid down first. because DNA polymerase lacks proofreading ability. Save Question 2 (0.5 points) What step(s) in polymerase chain reaction are necessary to emulate the action of the proteins that first assemble on the replication origin to pull apart the strands? O Cooling to-50C-65C O Heating to 94 Warming to 72C none of the above Save

Answer 1

Answer :

1. b. Because DNA polymerase can only add nucleotides to the 3' end of a chain of nucleotides and replication proceeds in both directions.

The helicase unzips the double stranded DNA for replication, making a forked structure. The primase generates short strands of RNA that bind to the single-strnded DNA to initiate DNA synthesis by the DNA polymerase. This enzyme can work only in the 5' to 3' direction , so it replicates the leading strang continuously. Lagging strand replication is discontinuous, with short okazaki fragments being formed and later linked together.

2. b) Heating to 94C

The PCR technique is used to amplify large quantities of a specific sequence of DNA from an initial minute sample. Each reaction doubles the amount of DNA - a strandard PCR sequence of 30 cycles creates over 1 billioncopies.

The process via three steps:

1. Denaturation - DNA sample is heated (approximately 90C 0to separate the strands.

2. Annealing - Sample is cooled (approximately 55C) to allow primers to anneal .

3. Elongation - Sample is heated to the optimal temperature for a heat- tolerant polymerase(taq) to function(aproximately 75C)