Theme 1-c Flashcards
What is the semiconservative model
each daughter strand remains paired with its complementary parental strand
What is the conservation model
After replication both daughter strands pair up
What is the dispersion model
daughter strand will have a mixture of parental and newly synthesized dna
What is the purpose of the Meselson and stahl experiment
After the Watson and crick hypothesized the semiconservative model this experiment drove it
How does the meselson and stahl experiment work
First the took ecoli and put it in a heavy nitrogen isotope called N15, causing all nitrogen contain molecules (including DNA) to become heavy
This means if coli cells grown in N14 media and subject its dna to density gradient centrifugation the N15 willl have higher density then N14
N15 cells where then transferred to N14 medium to replicate. They harvest cells every 20 minutes, isolated the Dna and subjected it density gradient centrifugation
What was the results ofmeselson and stahl experiment
After the first round dna appeared as a single band intermediate between where N15 and N14 are normally found this indicated that N115 Dna strand was acting as a template for new N14 strand
As cell continues to replicate more n-14 is in it’s dna causing there to be more n14 where the n14 is normally found
What direction are nucleotides added
New nuclotides can only be added to 3’OH groups Dna synthesis occurs in a 5’ to 3’ direction
In order to have energy to do this 2 phosphates are cleaved of to form atp in order to have enough energy for new phosphodiester bond
How does DNA polymerase work
Synthesized the new dna strand only in 5’ t0 3’ direction so the parental strand is read in the 3’ to 5’ direction
This requires a dna primer with a 3’ oh to begin
Has a single active site that can catalyze 4 reactions
Why are telomeres necessary
Being that we need ran primers in order for dna polymerase to work for 3’ to 5’ end this becomes a problem because no polymerase can fill gaps at chromosomal ends to solve this telomeres are added to the end
What are telomere
non coding single stranded DNA usually relearn 5-8 G’s and T’s
What happens when telomeres get all used up
Therefore when telomeres are all used up cells stop dividingTherefore when telomeres are all used up cells stop dividing
What is telomerase
restores shortened telomeres , nor present in most eukaryotic cells
present in gametes and stem cells
