DNA replication and repair Flashcards
nucleotides
building blocks of nucleic acids
what are nucleotides composed of
a nitrogenous base, pentose sugar, and a phosphate group
phosphodiester bond
links 2 pentose groups
the complementary nitrogenous bases between the two nucleic acids interact via
hydrogen bonding
when is dna replicated
s phase of interphase
main steps of dna replication
- initiation
- elongation
- termination
initiation
- Helicase unwinds a section of the double helix to separate the two strands to make them available for new base pairing
- Each strand is primed with an RNA primer with the help of Primase
replication fork
he two separated nucleic acid strands ready to be replicated
elongation
- DNA synthesis occurs from the RNA primers with the addition of nucleotides that form
complementary base pairs with the original DNA strand - Incoming nucleotides are linked by phosphodiester bonds
consequence of DNA polymerase III only adding nucleotides into the elongating new strand from the 5’ to 3’ direction
there will be a leading strand and a lagging strand
leading strand
replication begins immediately in a continuous manner
lagging strand
replication occurs discontinuously and is slower because it has to “wait” for the DNA double helix to unwind
Okazaki fragments
the discontinuous strands in the lagging strand; will later be joined together by DNA ligase
termination
- RNA primers are removed and replaced with deoxyribonucleotides via the action of RNAse H
- DNA synthesis ends when all the DNA has been replicated.
dna replication in prokaryotes
Occurs from a single origin of replication (ori)
Contrast: there is more than one ori in eukaryotes
* Unwinding of DNA is relatively simple since prokaryotic chromosomes do not have histones
* Makes use of prokaryotic versions of the enzymes involved in DNA replication
