DNA Replication

Question 1

Sliding Clamp structure

Answer 1

A protein ringt encircling DNA helix

Question 2

Sliding Clamp function

Answer 2

ALlows DNA polymerases to remain attached to their DNA template so DNA P. can synthesis long stretches efficiently without falling off template

Question 3

The trombone model

Answer 3

Lagging strand template loops back through replisome so leading + lagging strand synthesis in same 5’ to 3’ direction

Question 4

SSB function

Answer 4

ssDNA between Okazaki fragments is bound by ss binding protein -> once DNA p reaches upstream RNA primer, lagging strand loop released

• > a new loop is formed once primase on lagging strand makes new primer
• > loop is release after each Okazaki fragment

Question 5

Splicing is a _____ reaction

Answer 5

Transesterification

Question 6

Splicing characteristics

Answer 6

No net input of energy

• catalysed by spliceosome
• 5 SnRNP’s - U1-5

Question 7

Spliceosome recognises

Answer 7

GU sequence at 5’ end and AG sequence at 3’ end
+ branch point A in intron
+ polypeptide track upstream of AG 10-20 nt

Question 8

SnRNP’s and protein factors attach to ____

Answer 8

AG seq. at 3’ end for recognition

Question 9

Splicing mech:

Answer 9

1. Spliceosome forms at recognition site
2. Precuror mRNA undergoes structural rearrangement
3. 2’OH of adeno sequence residue located within the intron attacks exon 1 intron banding
4. Branched intron structure -> loriat
5. Spliceosome brings exon 1 and exon 2
6. Newly released 3’OH exon attack intron-exon 2 junction
7. Loriat released