T4M2- DNA replication and mitosis Flashcards
what type of structure is DNA present in
helical
what types of bonds are present between template strands
hydrogen bonding
what type of model is DNA
semi conservative
describe the semi conservative model for replication
one old and one new strand in each daughter
who demonstrated that DNA replicates in semi conservative manner
Matthew Melelson and Frankin Stahl
Describe Melelson and Stahl’s experiment
Cultured e coli bacteria cells for generations with nucelotide precursers with N15
- transferred bacteria to medium with N14
- extracted samples and centrifuged to separate DNA based on density
Where was the band on the N15?
sat lower due to heavy density
where was the N14 band?
sat higher due to lower density
what model was ruled out
conservative model
in what direction is the template strand copied
3’ to 5’
in what direction does DNA synthesis occur
5’ to 3’
what type of bonding is in between complementary nucleotides
hydrogen bonding
what does the incoming nucleotide interact with
3’ hydroxyl of polymer
what type of bond forms between new daughter strand and incoming nucleotide
phosphodiester bond
where does unwinding occur and what does it separate
the separation of the parent strands at replication fork within origin of replication
what does initiation require and why
short RNA primer- to synthesize and base pair with template DNA
what enzyme catalyzes the polymerization of each daughter strand
DNA polymerase
describe the leading strand
- continuous
- needs only one primer and DNA polymerase can add nucleotides to new daughter cell
describe the lagging strand
- anti parallel
- has fragmented or discontinuous DNA
in which direction does DNA synthesise in lagging strand
5’ to 3’
what is formed along the lagging strands
okazaki fragments formed by separate primers
what enzyme binds to parental DNA to initiate unwinding of double helix
DNA helicase
what does DNA helicase do
breaks hydrogen bonds between base pairs
what stabilizes DNA from rejoining after unwinding
single stranded binding proteins
describe the function of topoisomerase
binds upstream replication fork to ease tension produced at unwinding
role of RNA primase
synthesizes short RNA stretches of nucleotides complementary to parental strands
role of DNA polymerase iii
does most of elongation work in prokaryotes
role of DNA polymerase i
removes primer after RNA primer and replaces with nucleotides
how many origins of replication are in prokaryotes
one region of replication
what does DNA ligase do
joins 3’ end of fragment to adjacent DNA nucleotide by catalysing phosphodiester bond, forming okazaki fragments
what happens if the wrong nucleotide is added during replication
DNA polymerase replaces it
how does replication occur in prokaryotes
at one site of replication- and continues in circular chromosome
what way is elongation
5’ to 3’ end
why can RNA primer on lagging strand not be replaced with DNA nucleotides
no 3’ end available
what is present at the end of linear chromosomes
telomers
define telomeres
special sequences made of repetitions of one short nucleotide sequence
what is the telomere sequence
TTAGGG
what happens to the telomere sequence through times of replication
gets shorter and is used as a buffer to protect DNA- very short for the elderly
does telomere shortening affect gametes or stem cells?
no- they have telomerase enzyme to catalyze lengthening
what enzyme is a reverse transcriptase?
telomerase
what type of protein is telomerase
ribonucleic protein
where is DNA replicated
ori sites
