DNA replication Flashcards
what is the function of the enzyme DNA helicase
unzips DNA helix
breaks hydrogen bonds between complementary base pairs
creates new templates for new DNA strands
what bonds form between complementary base pairs
hydrogen bonds
what is the function of DNA polymerase
links free adjacent nucleotides to form complementary base pair
where are phosphodiester bonds formed between
formed between nucleotides in condensation reactions
what reaction joins nucleotides together
condensation reactions
define semi-conservative replication
replication where each of the two DNA molecules made contains one original strand (from parent DNA) and one new strand
what does DNA ligase do
closes any gaps in the strand that might have been missed
- (joins complementary base pairs that may not have paired up)
what is the full process of DNA replication
DNA helicase breaks hydrogen bods between bases and molecule unwinds and separates two strands
both strands act as a template
free nucleotides line up against CBP on both strands
hydrogen bonds form between bases
DNA polymerase joins adjacent nucleotides by phosphodiester bonds in condensation reactions
DNA ligase closes any gaps in the strand
two new DNA molecules are formed which are identical to each other and parent strand
what were the three ways that DNA was thought to be replicated
semi- conservative
conservative
fragmentary
define fragmentary replication
all DNA strands are made up of a mixture of original parent DNA nucleotides and new nucleotides
define conservative replication
one DNA molecule has two original parent DNA strands and the other molecule has two new strands
what happens to bacteria when grown in 14N
forms band at top of the tube since its light
what happens to bacteria when grown in 15N
forms a band at the bottom of the tube since its heavier
practical carried out to prove DNA replicates semi-conservatively
scientists took sample of bacteria with almost all nitrogen atoms in DNA being 14N (lighter isotope)
extracted DNA placed it in a solutions and centrifuged it (spun it)
DNA formed band near the top of the tube
next scientists replicated bacteria in 15N (heavier nitrogen)
after bacteria had reproduced multiple times almost all nitrogen atoms in the DNA was 15N
this DNA was extracted and centrifuged
formed a band near the bottom of the tube (showing its heavy)
then scientists took a sample of heavy bacteria and transferred it into N14
let it replicate once
after replication they extracted DNA and centrifuged it
found DNA produced a band in the middle of the other two (medium)
this told scientists that one strand of DNA was heavy (N15) and one strand was light (N14)
means DNA must have replicated semi-conservatively one original (light) + one new strand (medium)
why is the fragmentary theory for DNA replication incorrect
it would only ever produce all medium bands of DNA
needs to be one medium and one light band for it to be correct (semi-conservative)
