Structure and Replication of DNA

Question 1

DNA structure

Answer 1

2 anti-parallel strands of repeating units called nucleotides twisted into a double helix.

Question 2

DNA nucleotide structure

Answer 2

Consist of deoxyribose sugar, phosphate, and a base (guanine, cytosine, adenine, thymine)
Deoxyribose in a nucleotide has a base attached to its carbon 1 and a phosphate attached to its carbon 5.

Question 3

Complementary base pairs

Answer 3

Guanine pairs with cytosine
Adenine pairs with thymine

Question 4

DNA polymerase

Answer 4

Before a cell divides the DNA gets replicated by DNA polymerase.

Question 5

Primer

Answer 5

A short strand of nucleotides which binds to the 3’ end of the template DNA strand allowing polymerase to add nucleotides.

Question 6

DNA replication stage 1

Answer 6

DNA double helix unwinds

Question 7

DNA replication stage 2

Answer 7

Weak hydrogen bonds between base pairs break to form two template strands.

Question 7

DNA replication stage 3

Answer 7

DNA polymerase can only add DNA nucleotides in one direction - the deoxyribose (3’) end of the new DNA strand.

Question 7

DNA replication stage 4

Answer 7

This results in the leading strand being replicated continuously and the lagging strand being replicated in fragments.

Question 8

DNA replication stage 5

Answer 8

Ligase enzyme joins the fragments together.

Question 9

DNA replication requirements

Answer 9

-DNA (to act as template)
-Primers
-DNA nucleotide
-Enzymes
-ATP

Question 10

PCR

Answer 10

Polymerase Chain Reaction amplifies DNA using complementary primers for specific target sequence.

Question 11

Primers in PCR

Answer 11

The primers, in PCR are short strands of DNA nucleotide which are complementary to specific target sequences at the two ends of the region of DNA to be amplified.

Question 12

PCR procedure

Answer 12

PCR involves repeated cycles of heating and cooling of the target region of DNA to be amplified.

Question 13

PCR stage 1

Answer 13

DNA is heated to between 92 and 98 to separate the strands.

Question 14

PCR stage 2

Answer 14

DNA then cooled to between 50 and 65 to allow the primers to bind to target sequences

Question 15

PCR stage 3

Answer 15

DNA is then heated to between 70 and 80 for heat tolerant DNA polymerase to replicate the target region of DNA.

Question 16

Uses of PCR

Answer 16

PCR can amplify DNA to help solve crimes and settle paternity suits and genetic disorders can be diagnosed.