DNA Flashcards
1
Q
what are the key features of DNA structure
A
- double stranded helix
- right handed helix
- antiparallel
- held together by complementary base pairing
- outer edges of bases exposed in major and minor grooves
2
Q
why is the double helix structure essential to DNA function
A
- base sequence stores huge amounts of genetic information
- precise replication in cell division is possible by complementary base pairing
- nucleotide sequence determines amino acid sequence determines proteins = phenotypes
3
Q
what is semiconservative replication
A
each parent strand is a template, so new molecules have one old and one new strand
4
Q
what are the 3 steps of DNA replication
A
- initiation
- elongation
- termination
5
Q
what happens in the initiation step of DNA replication
A
- DNA replication starts at ori site
- DNA helicase uses energy from ATP hydrolysis to unzip DNA
- single-stranded binding proteins prevent strands from getting back together
- primase enzyme synthesises a shirt RNA strand primer that binds to unzipped DNA
- DNA polymerase comes to the primer site + begins elongation
6
Q
what happens in the elongation step of DNA replication
A
- leading strand grows at the 3’ end
- at the lagging strand an unreplicated gap forms
- synthesis of lagging strand occurs in discontinuous stretches = Okazaki fragments
- DNA polymerase III, DNA polymerase I, DNA ligase elongate strands
- polymerase-DNA complex is stabilised by a sliding DNA clamp
7
Q
what happens in the termination step of DNA replication
A
- DNA replication takes place at the ter site (prokaryotes)
- ## once terminal Okazaki primer is removed, no DNA is synthesised
