DNA replication

Question 1

What are the 3 problems a cell encounters when it needs to reproduce?

Answer 1

1. Getting the two DNA strands apart
2. Making two new DNA strands
3. Attaching the pieces of the discontinuous strand together

Question 2

What is the solution for problem #1 and how does the cell solve it?

Answer 2

Solution: DNA helicase

How?: DNA helicase will open up a replication bubble at the origin of replication. The replication bubble is expanded in both directions by DNA helicase (like a zipper).

Question 3

What are replication forks?

Answer 3

It is where the DNA is separated to make a bubble.

Question 4

What is the solution for problem #2 and how does the cell solve it?

Answer 4

Solution: DNA polymerase

How?: DNA polymerase reads the nucleotide making up the single strands of DNA and uses them as a template to make new strands; adds nucleotides that are complementary to the nucleotides it reads on the original strand (sees an A, will add T).

Question 5

In what direction is DNA polymerase adding nucleotides? And in what direction is it moving on the DNA template strand?

Answer 5

5’ end —-> 3’ end
on the strand: 3’ end —-> 5’ end

Question 6

What is the name of the strand that is made continuously?

Answer 6

The leading strand

Question 7

What is the name of the strand that is made discontinuously?

Answer 7

The lagging strand

Question 8

What are the discontinuous strands called?

Answer 8

Okazaki fragments

Question 9

What is the solution for problem #3 and how does the cell solve it?

Answer 9

Solution: DNA ligase

How?: DNA ligase wraps around the double helix like a wristwatch and attaches the fragments.

Question 10

What is the use of Polymerase Chain Reaction (PCR)?

Answer 10

DNA analysis requires relatively large amounts of DNA, but PCR creates a lot of DNA copies of a very small sample of DNA, making analysis possible (does not require cells, in vitro).

Question 11

What are the steps of Polymerase Chain Reaction (PCR)?
(DNA replication)

5

Answer 11

1. The initial DNA sample is mixed with primers, free single nucleotides, and Taq DNA polymerase
2. Mixture is heated, separating the DNA (replaces DNA helicase)
3. Mixture is cooled and primers bind to their complementary strand
4. Taq DNA polymerase starts at the primers and copies the DNA on each strand
5. Cycle is repeated