DNA replication Flashcards
Nucleotide vs nucleoside
nucleotide also contains a phosphate
Erwin Chargaff rule
A=T AND C=G (a+tnot equals c+g)
What keeps the bases together in DNA
3-5
phosphodiester bonds
Three major forms of DNA
B-form, right handed
A-form- dehydrated
z-form, lefthanded
Hyperchromocity of DNA
ds= lower absorbance
ss= higher absorbance
Mitochondrial DNA
circle
one strand being “heavy” (H strand) and ight (the L strand).
Both strands encode genes, although more are on the H strand.
37 genes (2 rRNA, 22 tRNA, 13 polypeptides
The D loop is also the site where most of replication and transcription is controlled.
Genes are tightly packed, with almost no non-coding DNA outside of the D loop
Human mitochondrial genes contain no introns, although introns are found in the mitochondria of other groups (plants, for instance).
Prokaryotic DNA Polymerases (E. coli)
Pol I - Gap filing
Pol II - proofreading
Pol III leading strand
Eukaryotic DNA polymerase
Pol A:DNA Replication (Primer Synthesis)
POl B: Base excision repair
POL GAmma:Mitochondrial DNA replication/repair
POLsigma: DNA Replication; nucleotide and base excision repair
POl delta: DNA Replication; nucleotide and base excision repair
Tautomer formation
A pairing with T, but here A pairs with C, that pairs with G. Mutation happens
Initiation
Involved are: DnaA·ATP: find Ori DnaB (helicase) DNA G- Rna primer synthesis SSBs
Elongation
Leading strand
DnaB (helicase)
DnaG (primase)
DnaC (pol III)
Lagging strand DnaG/B “primosome” SSBs DNA Pol I and III DNA Ligase
Mechanism of DNA Ligase
- Adenylation of DNA ligase
- Activation of 5`Phosphate in nick
- Displacement of AMP seals the nick
Termination
Counterclockwise fork
Clockwise fork
Topoisomerase
unlink parental strands
Top 1 (no atp)and 2(ATP) in EU
top 1 in pro
DNA gyrase
creates supercoils in DNA which stabilizes the DNA (requires ATP)
Telomerase
adds DNA sequence repeats to the 3’ end of DNA strands in the telomere regions, which are found at the ends of eukaryotic chromosome
The Meselson–Stahl experimen
DNA replication was semiconservative. In semiconservative replication, when the double stranded DNA helix is replicated each of the two new double-stranded DNA helixes consisted of one strand from the original helix and one newly synthesized.
Packing of DNA in Eukaryotes
The double stranded DNA is wrapped around each nucleosome twice. Each is made up of Histones which have 2 functions:
1) compact DNA
The double stranded DNA is wrapped around each nucleosome twice. Each is made up of Histones which have 2 functions:
1) compact DNA
2) prevent RNA polymerase from binding to promoter
DNA ligase
facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond.