3. DNA replication
occurs during the S
phase of mitosis.
5
’
phosphate
sugar
phosphate
Thymine
Adenine
phosphate
sugar
Cytosine
Guanine
Guanine
Cytosine
Adenine
Thymine
Adenine
Thymine
Guanine
Cytosine
Thymine
Adenine
sugar
sugar
phosphate
Cytosine
Guanine
phosphate
3
sugar
phosphate
phosphate
sugar
sugar
phosphate
phosphate
sugar
sugar
phosphate
phosphate
sugar
sugar
phosphate
phosphate
sugar
sugar
phosphate
phosphate
sugar
base make up a nucleotide.
Each base pair is linked by
a hydrogen bond and these
bonds are easily broken.
phosphate
phosphate
sugar
sugar
3
’ The phosphate, sugar and
sugar
phosphate
Guanine
Cytosine
sugar
5
4. 5
’
On the lagging
strand, that
stretches away
from the
replication fork,
DNA polymerase
Phosphate
sugar
Phosphate
Thymine
sugar
Adenine
Phosphate
Phosphate
sugar
Cytosine
sugar
Guanine
Guanine
Cytosine
Phosphate
Phosphate
This is the
leading
strand.
sugar
Guanine
sugar
Phosphate
Binding proteins sugar Adenine
bind to a singlestrand DNA for Phosphate
stabilization.
sugar Adenine
Thymine
sugar
Phosphate
Thymine
sugar
Phosphate
Helicase
Cytosine
Thymine
Adenine
Phosphate
Cytosine
sugar
sugar
Phosphate
Phosphate
sugar
sugar
Guanine
This is the
lagging
strand.
sugar
Phosphate
Guanine
sugar
Phosphate
Phosphate
3
DNA primase marks a
starting point with an
RNA primer to the
lagging strand.
Double stranded DNA is
“unzipped” by DNA helicase.
Helicase unwinds doublestranded DNA at the origin
of replication by breaking the
weak hydrogen bonds
between the two strands.
Phosphate
Phosphate
sugar
3
’
Cytosine
sugar
5
8. At the end of our genes there are telomeres and they protect our genetic data and
makes it possible for a cell to divide. Every time a cell divides the telomeres get
shorter and when they become too short the cell can’t divide, it becomes inactive
or it dies and the shortening process is associated with a higher risk of death,
aging and cancer. The enzyme telomerase adds bases to the telomeres so they
don’t become to short and when the cell continues to divide the cell we slowly
run out of telomerase and telomerase is always in reproductive cells so the next
organism has telomerase to keep the organism alive and without telomerase in
the reproductive cells the living things without it would go extinct. We can use
telomerase to make human cells immortal and would be able to mass produce
cells for transplantation like insulin producing cells to cure diabetes, skin cells to
heal burns and wounds, and cartilage cells for some types of arthritis. There are
people trying to clone human telomerase.