Topics covered in this study guide:
• Intricacies of DNA replication
• The role of telomeres and telomerase
• Describe mechanisms of DNA repair & what happens if they are defective.
Topics covered in this study guide:
• Intricacies of DNA replication
• The role of telomeres and telomerase
• Describe mechanisms of DNA repair & what happens if they are defective.
Pictures are pretty good quality, so just zoom in to see them, they’re really useful.
I would also highly recommend watching the short videos attached to get a better understanding of the
concepts discussed.
Preview
“No limit of thinking, No limit of abilities, That is the way to achieve more in life”
― Saif Rehman
Summarise DNA replication in 3 Steps:
1. DNA is unwound by helicase.
2. The two DNA strands form templates and free complementary nucleotides are added to form the
daughter DNA strands. One strand is formed continuously while the other strand is formed in
fragments. This step is initiated by primers.
3. The primers and removed and replaced with DNA nucleotides by DNA polymerase. All the
fragments are joined together by DNA ligase.
1| Generation of Genes @barbstudy
, DNA Replication
def. the cell makes copies of itself and daughter cells receive identical copies of DNA during cell division.
When? During the S-phase of the cell cycle
Make sure you know how: to write a complementary base sequence.
3 models of DNA replication:
Conservative Semiconservative Dispersive
DNA molecule Two DNA strands The DNA
is a template separate and each backbone
for the strand acts as a breaks after
synthesis of a template for the every 10
completely new new DNA nucleotide
DNA molecule. molecule forming. bases,
The strands are Therefore, each untwists and
exposed from new DNA new
the histone for molecule consists nucleotides
replication and of an old strand attach
then retain their and a new one themselves to
original the strands of
position. the old end.
How did we prove that
semi-conservative was
the one?
Meselson-Stahl
Experiment
Why nitrogen? DNA bases are made of nitrogen.
Meselson-Stahl Experiment
Basically, growing generations of bacteria in different
isotopes of Nitrogen to distinguish between parent and
daughter strands.
Details:
1. E. coli was placed in a medium containing ‘heavy’
nitrogen (N15) and left to replicate until all of
bacteria had N15 incorporated in their DNA.
2. The same bacteria were then transferred to a
medium containing N14, an isotope of nitrogen
with a lower density.
3. The sample was centrifuged after every generation
of replication. During centrifuging, the DNA
samples would move to the bottom of the beaker
according to its density.
2| Generation of Genes @barbstudy
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