DNA structure, function and replication Flashcards
describe prokaryotic replication…
binding protein (DNAa) starts the process at a single point of origin (oriC)
parental strands separate and form a bubble
strands are copied simultaneously in opposite directions
replication ends at termination point - DNA is circulised by ligases (joins things together)
cell divides
describe eukaryotic replication…
- DNA in nucleus condenses - bound to proteins.
- chromatin condenses into chromosomes
- DNA opens at the replication fork
- each parent strand copied into a complementary daughter strand
- new DNA made behind the fork and is semi-conservative.
describe new strand production in more detail…
DNA unwinds on one side with the leading strand polymerase printing 5’-3’. the lagging strand on the other side cannot so okazaki fragments form.
(small fragments allowing polymerase to pring in small chains with gaps)
RNA primers are removed, gap filled by DNA polymerase. joined to okazaki fragments by ligase.
which direction does polymerase read?
reads 3’-5’ and prints 5’-3’.
what does helicase do?
opens the DNA strand
what do SSB proteins do?
single stranded binding proteins - stop the DNA sticking back together.
what does topoisomerase do?
unwinds the DNA strand.
turns supercoiled DNA into uncoiled DNA
whatt does ligase do?
joins DNA strands by catalysing the formation of phosphodiester bonds
what does nuclease do?
cleaves chains of nucleotides into smaller units
what does primase do?
synthesises short RNA sequences called primers - serve as a starting point for DNA synthesis
what happens in general DNA when replication first occurs?
bubbles form and extend until they are all joint by ligase
what are the stages of PCR?
- DNA heated to separate
- cooled and primers are added
- DNA polymerase added and free nucleotides
- heated for annealing and then cycle repeated
