2. replication of DNA

Question 1

what happens to DNA prior to cell division

Answer 1

it must be replicated exactly by the enzyme polymerase

(DNA replication takes place at various points along the DNA molecule, simultaneously)

Question 2

what is a primer

Answer 2

a short strand of DNA which binds to the 3’ end of the template DNA strand

Question 3

what is a polymerase chain reaction (PCR)

Answer 3

an automated process that amplifies DNA using complementary primers for specific target sequences

practical applications of PCR are that it can amplify DNA to help solve crimes, settle paternity suits and diagnose genetic disorders

Question 4

where does DNA replication occur

Answer 4

at various points on a DNA molecule

Question 5

describe primers in PCR

Answer 5

short strands of nucleotides which are complementary to specific target sequences at the two ends of the region of the DNA to be amplified

Question 6

describe the stages of PCR

Answer 6

during PCR there are repeated cycles of heating and cooling to amplify the DNA

• stage 1: DNA (double stranded) is heated to between 92 and 98C to separate the DNA strands
• stage 2: DNA is then cooled to between 50 and 65C to allow primers to bind to target sequences
• stage 3: it is then heated to between 70 and 80C for heat-tolerant DNA polymerase to replicate the region of DNA

Question 7

describe the 5 stages of DNA replication in living cells

Answer 7

-DNA is unwound (by helicase) and hydrogen bonds are broken between the bases to form two template strands

-the enzyme DNA polymerase needs primers to start replication

-the primer allows DNA polymerase to add nucleotides, using complementary base pairing, to the 3’ end of the primer/new strand that is forming

-DNA polymerase can only add nucleotides in one direction (5’ to 3’), resulting in the leading strand being replicated continuously and the lagging strand replicated in fragments

-the fragments of DNA (on lagging strand) are joined together by ligase