DNA Replication Flashcards
Sliding Clamp structure
A protein ringt encircling DNA helix
Sliding Clamp function
ALlows DNA polymerases to remain attached to their DNA template so DNA P. can synthesis long stretches efficiently without falling off template
The trombone model
Lagging strand template loops back through replisome so leading + lagging strand synthesis in same 5’ to 3’ direction
SSB function
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
Splicing is a _____ reaction
Transesterification
Splicing characteristics
No net input of energy
- catalysed by spliceosome
- 5 SnRNP’s - U1-5
Spliceosome recognises
GU sequence at 5’ end and AG sequence at 3’ end
+ branch point A in intron
+ polypeptide track upstream of AG 10-20 nt
SnRNP’s and protein factors attach to ____
AG seq. at 3’ end for recognition
Splicing mech:
- Spliceosome forms at recognition site
- Precuror mRNA undergoes structural rearrangement
- 2’OH of adeno sequence residue located within the intron attacks exon 1 intron banding
- Branched intron structure -> loriat
- Spliceosome brings exon 1 and exon 2
- Newly released 3’OH exon attack intron-exon 2 junction
- Loriat released