DNA Flashcards
how did we figure out it was DNA and not protein as the genetical material
studying radioactive virus DNA and phages, seeing if radioactive phages came out of the bacteria
what is the stricture of DNA nucleotides
a deoxyribose sugar (5 carbon) with a nitrogenous base attached to the 1’ and a phosphate group attached to the 5’
what are purines
a type of nitrogenous base that has 2 rings
adenine and guanine
what are pyrimidines
a nitrogenous base that has one ring
thymine and cytosine
what type of bond links the DNA nucelotides
phosphodiester bond
how do DNA strands form together
double helix format
hydrogen bonds linking the bases (C-G with 3 H bonds, A-T with 2)
running in opposite ends of the other
(at top one strand starts as a 5’ and the other a 3’)
what is the conservative model of DNA replication
belief that once replicated one has both parental strands and the other has both replicated strands
what is the dispersive model of DNA replciation
both strands have interspersed segments of both parental and replicated DNA
(chopped up and spliced together)
what is the semiconservative model of DNA replication
each strand has one parental and one replicated strand
which model of DNA replication is true
semiconservative model
what was the test to see which model was true
soaking DNA in heavy nitrogen and then during replication switching it to a lighter nitrogen and then seeing which replication had what nitrogen
where are parental strands separated
at multiple origins of replication
what is a replication bubble
bubble that occurs at the origins of replication when they are separated
which direction does replication occur in at the origin of replication
both directions, bidirectional
what synthesizes the new DNA strand
DNA polymerase
true or false: DNA polymerase can add nucleotides to the 5’ end
false, they can only add to the 3’ end
what does the sliding clamp do
holds the DNA polymerase into the template strand
what direction does synthesis occur in on each separate strand
from the 5’ to 3’ end for the daughter strand
(starting from the 3’ end on the parental strand)
what is the leading strand
the strand that synthesizes towards replication fork where synthesis is a continuous strand towards the fork along the leading strand template
what is the lagging strand
the strand that synthesizes away from the replication fork through discontinuous synthesis fragments
what are the fragments of the lagging strand called
Okazaki fragments
what enzyme unwinds the double helix and how
helicase breaks down hydrogen bonds between base pairs
what is the job of the topoisomerase
stops extra coiling of DNA resulting form the helicase by swiveling and rejoining the DNA strands ahead
what keeps the separated DNA strands from separating
single stranded binding proteins
what does the primase do
places RNA primers and removes the single-stranded binding proteins locally in the process
why do we need an RNA primer
to get the new replicated strand started by having an exposed 3’
what does the DNA polymerase 3 do
begins making the daughter strand by placing DNA nucleotides
true of false: the lagging strand needs multiple RNA primers compared to the leading strand
True, leading strand only needs one as it has a continuous synthesis
what does DNA polymerase 1 do
attaches the Okazaki fragments and removes the nucleotides of the RNA primer with DNA nucleotides
what does the DNA polymerase leave behind
a nick between the strands it fixes
how do we fix a nick in the DNA strand
using the DNA ligase that completes the phosphodiester bond, once done the ligase leaves
