chapter 12 Flashcards
(31 cards)
semiconservative replication
only one sequence of bases can be specified by each template strand so the two DNA molecules built on the pair of templates will be identical to the original
- each of the original nucleotide strands are conserved
conservative replication
the entire double stranded DNA molecule serves as a template for a whole new molecule of DNA and the original molecule is fully conserved during replication
Dispersive replication
both nucleotide strands break down into fragments which serve as a template for the synthesis of new DNA
Meselson and Stahl Experiment
using isotopes of nitrogen and spun in a centrifuge and demonstrated that DNA replication is semiconservative - each DNA strand serves as a template for the synthesis of a new DNA molecule
how many origin of replication do bacterial chromosomes have
only one
replication fork
the point of unwinding where the two strands separate from the double-stranded DNA helix
bidirectional replication
if there are two replication forks, one at each end of the replication bubble, the forks proceed outward in both direction
what happens in the process of replication
- dna molecule unwinds to expose the bases that act as a template strand
- in dna synthesis, nucleotides are added to the 3’ OH group of the growing nucleotide strand
‘ 3’OH group strand attacks the 5’ phosphate group of upcoming dNTP and two phosphate groups are cleaved and phosphodiester bond is created between two nucleotides
what direction is DNA synthesis
5’ to 3’
what is the new strand that undergoes continuous replication called
leading strand
where does synthesis proceed in replication
exposed in the 5’ to 3’ direction and opposite of the unwinding
what is the newly made strand that undergoes discontinuous replication called
lagging strand
Okazaki fragment
shorter fragments of DNA produced by discontinuous fragments
four stages of replication
initiation, unwinding, elongation and termination
what happens during initiation
Initiator proteins bind to the origin of replication
- causes a short stretch of DNA to unwind
- the unwinding allows helicase and other single strand binding proteins to attach to the single stranded DNA
what happens during unwinding
DNA synthesis requires double stranded DNA to be unwound; to be single strand
DNA helicase
breaks the hydrogen bonds between the bases of the two nucleotide strands of DNA molecule
- initiator protein first separates DNA strands at origin and then helicase unwinds
single-stranded binding proteins
attach tightly to the exposed single stranded DNA and protect the nucleotide chains and prevent structures from interfering with replication
DNA gyrase
- a topoisomerase which reduces the torsional strain that develops as the two strands of dna unwins
elongation
- single stranded DNA is used as template for synthesis of dna
primase
synthesizes short RNA primers which provides 3’-OH group to which DNA polymerase can attach DNA nucleotides
- primers are later removed and replaced with DNA nucleotides
DNA polymerase I
removes and replaces primers DNA repair; restarts replication after damaged DNA halts synthesis
DNA polymerase III
elongates DNA by adding nucleotides to the 3’ end of growing DNA strand
dna ligase
joins okazaki fragments by sealing breaks in the sugar phosphate backbone of newly synthesized dna
