DNA Flashcards
(14 cards)
what are the key features of DNA structure
- double stranded helix
- right handed helix
- antiparallel
- held together by complementary base pairing
- outer edges of bases exposed in major and minor grooves
why is the double helix structure essential to DNA function
- 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
what is semiconservative replication
each parent strand is a template, so new molecules have one old and one new strand
what are the 3 steps of DNA replication
- initiation
- elongation
- termination
what happens in the initiation step of DNA replication
- 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
what happens in the elongation step of DNA replication
- 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
what happens in the termination step of DNA replication
- DNA replication takes place at the ter site (prokaryotes)
- once terminal Okazaki primer is removed, no DNA is synthesised
- chromosome becomes shorter with each replication
- after many divisions the genes may be lost
What are 4 mechanisms of repair of DNA
- proofreading
- mismatch repair
- excision repair
- homologous recombination
What is proofreading of DNA
DNA polymerase recognises mismatched pairs and removes incorrectly paired bases
What is mismatch repair in DNA
Newly replicated DNA is scanned for mistakes by other proteins + mismatches can be corrected
What is excision repair DNA mechanism
Enzymes scan DNA for damaged bases, excised and DNA polymerase I adds the correct ones
What is the homologous recombination repair mechanism
Breask in DNA strands can be repaired by copying from the sister chromosome
What is PCR
An automated process makes multiple copies of short DNA sequences for genetic manipulation + research
What does a PCR mixture contain
- double stranded DNA template
- 2 artificially synthesised primers
- 4 nucleotides
- DNA polymerase that can tolerate high temps (Taq)
- salts + pH buffer
