DNA, protein and central dogma

Question 1

DNA replication

Answer 1

-every time cell divides, a complete copy of the DNA is needed for the new cell
-happens semi-conservatively
1. DNA strands are separated into single strands
2. the strands now act as a template for a new complementary strand

Question 1

Bacterial DNA replication

Answer 1

-starts at ‘origin’ and proceeds in both directions until entire chromosome has been copied

Question 2

eukaryotic DNA replication

Answer 2

many simultaneous ‘replication bubbles’. Replication bubbles expand in both directions and fuse as copying of daughter strand is completed

Question 3

Unwinding the double helix without creating knots

Answer 3

-helicase
-topoisomerase
-single strand binding proteins
-DNA primase

Question 4

helicase

Answer 4

helicase untwists the DNA helix to give single stranded DNA, but increases coiling ahead of the replication fork

Question 5

topoisomerase

Answer 5

‘fixes’ the increased coiling in the DNA template- takes knot and breaks the 2 strands of DNA allowing the 2 strands to rotate around each other

Question 6

single strand binding proteins

Answer 6

stabilises the single stranded template

Question 7

DNA primse

Answer 7

synthesises RNA primer at the 5’ end

Question 8

How is new DNA synthesised

Answer 8

-uses nucleotide building blocks
-5’ to 3’ direction
-DNA polymerase catalyses DNA synthesis
-2 DNA strands that are being replicated are referred to as the ‘leading’ and ‘lagging’ strand

Question 9

DNA replication proceeds at replication fork

Answer 9

-bases added in only one direction
-single direction of base addition creates problems for replication process -> leading and lagging strand during RNA replication
-each replication fork produces new DNA -direction movement dictates lagging and leading

Question 10

synthesis of leading strand

Answer 10

-to start, DNA primase makes RNA primer
-DNA polymerase 3 extends RNA primer
-DNA polymerase 1 removes RNA primers, replaces with DNA

Question 11

synthesis of lagging strand

Answer 11

1. Primase joins RNA nucleotides into a primer
2. DNA polymerase 3 adds nucleotides, forming okazaki fragment 1 (DNA fragments)
3. DNA polymerase 3 detaches after reaching next RNA primer
4. fragment 2 is primed, DNA polymerase 3 adds nucleotides, detaches when reaches the fragment 1 primer
5. DNA polymerase 1 replaces RNA with DNA, adds nucleotides to 3’ end of fragments 1 and 2
6. DNA, ligase bonds newest DNA to fragment 1 DNA
7. lagging strand complete

Question 12

ligase

Answer 12

joins DNA fragments together