5. Genes and Gene Expression - DNA replication

Question 1

what is the semi conservative DNA replication model?

Answer 1

the mechanism of replication where each new copy has one of the original strands

Question 2

how was radioactive isotopes of nitrogen used to discover the semi conservative DNA replication?

Answer 2

N15 (isotope) and N14 were used to distinguish the parental and daughter strands.

• nitrgoen used in ammonia which bacteria consumed and radioactive decay occured which was a marker

Question 3

DNA is synthesised from normal products of metabolism.

what are the precurosrs of purine and pyridine bases?

Answer 3

from amino acids

Question 4

DNA is synthesised from normal products of metabolism

where does deoxyribose derive from?

Answer 4

from glucose metabolism

Question 5

DNA is synthesised from normal products of metabolism

how does the synthesis of nucleosides occur?

Answer 5

require energy from ATP

Question 6

DNA is synthesised from normal products of metabolism

how does the addition of phosphates to nucleosides occur?

Answer 6

with energy from ATP

Question 7

define DNA synthesis

Answer 7

the formation of a phosphate ester bond linking two nucelotides

Question 8

what is the precursor for DNA synthesis?

Answer 8

deoxynuclioside triphosphates (DNTPs)

there are 4 of these, one for each DNA nucleotide.

Question 9

what are the two requirements for DNA polymerase reaction in vitro (test tube) for the DNA template? why are there these requirements? (2)

Answer 9

template must be either:

1. single stranded
2. double stranded with breaks on one strand.

this is because DNA polymerase needs a template to start copying the DNA (to make daughter strands in cell division)

DNA polymerase can only add a nucleotide to a free 3’-OH group

Question 10

why does DNA polymerase need a primer to replicate DNA (makes daughter strands)

Answer 10

DNA pol cant start a new chain. requires a primer thats about 8 nucleotides long to begin replication as DNA polymerase can only add nucleotides to an existing strand of DNA

Question 11

what are the three precursors required for DNA polymerase reaction?

Answer 11

1. all four DNTP’s when template strand is normal (ie has different bases)
2. if template strand has only a single nucleotide sequence, ie AAAAAAA, only one DTTP is needed
3. Mg2+ needed as a cofactor

Question 12

what does it mean that DNA polymerase is processive?

Answer 12

once DNA polymerase finds the free 3’OH group, it dissociates the N-glycosidic bond continuosly without leaving the DNA strand