DNA replication

Question 1

what does replicating the DNA ensure?

Answer 1

that the two daughter cells produced will both receive full copies of the parental DNA

Question 2

why is DNA considered to be semi-conservative? (4)

Answer 2

• because it is ‘half the same’
• in each new DNA molecule produced, one of the polynucleotide DNA strands is from the original DNA molecule being copied
• the other polynucleotide DNA strand has to be newly created by the cell
• therefore, the new DNA molecule has conserved half of the original DNA and used this to create a new strand

Question 3

what is the importance of retaining one original DNA strand?

Answer 3

it ensures there is genetic continuity between generations of cells, therefore when cells are replaced, they still do the same role as before

Question 4

what is the first step (and enzyme involved) in semi-conservative replication?

Answer 4

the enzyme helicase unwinds the DNA double helix by breaking the hydrogen bonds between the complementary base pairings on the two antiparallel polynucleotide DNA strands to form two single polynucleotide DNA strands

Question 5

what do the single polynucleotide DNA strands act as?

Answer 5

templates for the formation of a new strand made from free nucleotides that are attracted to the exposed DNA bases by base pairing

Question 6

how are the new nucleotides joined together?

Answer 6

by the enzyme DNA polymerase which catalyses the condensation reaction (between the deoxyribose sugar and phosphate group) to form the new strand

Question 7

how do the original and new strand join together?

Answer 7

through hydrogen bonding between base pairs to form the new molecule