Download DNA Replication

About how many cells are our bodies made of?
TRILLIONS!
How many of those cells
contain your DNA?
All of them! All of your cells
contain a complete copy of
your genome (DNA)!
Your life started as just 1 cell. How do we come from
1 cell & end up as trillions?
• That single cell divided over & over again as you grew.
• Every single cell needs copies of your DNA.
HOW DOES THAT
HAPPEN?
DNA Replication
DNA Replication
• The process of copying DNA
• Because DNA is double stranded, we
can separate the 2 strands & create
a new strand using 1 strand as a
template.
• Our end product is 2 identical
double stranded DNA molecules.
– The 2 strands are called
complementary.
During DNA Replication…
• The DNA is unwound & unzipped (the 2 strands separate).
• Each original DNA strand is used as a template (model) to
make a new DNA strand with base pairing.
Remember – Enzymes
• Enzymes are catalysts that speed up chemical
reactions.
• Forming & breaking chemical bonds takes energy.
– Enzymes lower the amount of energy needed to make &
break chemical bonds.
Enzymes in DNA Replication
• DNA replication could not occur without enzymes.
• There are several enzymes involved in this process.
Enzymes Used in DNA Replication
• Helicase unzips/separates the 2 DNA strands by breaking the
hydrogen bonds between the nitrogenous bases.
• DNA Polymerase adds new nucleotides to the new DNA strand.
– DNA Polymerase also “proofreads” the new DNA to check for
errors.
• The strands are rewound when the process is finished.
The Semi-Conservative
Method of Replication
• When replication is complete,
each DNA molecule is made of
1 old strand & 1 new strand.
Chromosome Arrangement in Prokaryotic Cells
(Bacteria)
• Prokaryotic cells have 1 circular
chromosome that is free-floating
in the cytoplasm.
– Prokaryotic cells do not have a
nucleus.
• When prokaryotic cells copy their
DNA, the process begins at 1
point in the chromosome &
moves around the circle in both
directions until complete.
Chromosome Arrangement in Eukaryotic Cells
• Eukaryotic cells have many chromosomes & DNA
replication begins at hundreds of places & continues in
both directions until each chromosome is completely
copied.
• The point in the DNA where the 2 strands are
separating & replication is occurring is called the
replication fork.
DNA Polymerase
•
DNA Polymerase only works in 1 direction (5’ to 3’).
–
One strand is read & synthesized continuously while the
other is synthesized in fragments.
DNA Polymerase makes the new strand from 5’ to 3’.
If DNA polymerase continues
in this direction (away from
the replication fork), what
will happen?
It will run out of DNA!
Once DNA polymerase gets to
the end, it loops back around
& starts another fragment.