DNA REPLICATION
DNA REPLICATION BASICS
DNA → in the nucleus of the cell → carries genetic information
↪ from the time we were a fertilized egg → every cell has had a
copy of it
Cell division occurs for:
- Growth → addition of new cells = make organism larger
- Repair of tissues through cell replacement
Each new cell requires a complete copy of the organism’s DNA → it
acquires it during DNA replication that occurs before cell
division (the only time)
Organism: from fertilized egg → large multicellular organism =
with an exact copy of the DNA
The same happens when repairing tissues:
New cells need to be produced →to replace those damaged or
destroyed
As wound heals → new cells are created to fill the place left in
the injury
↪ each an exact genetic copy
DNA of an organism → contains the instructions for that organism
↪ base sequences in it need to be copied exactly for new cells to
function properly
DNA in a cell → can be copied in 1 hour
SEMI-CONSERVATIVE NATURE OF DNA REPLICATION:
As one double strand of DNA is replicated → each new double strand
of DNA produced contains 1 strand of the original DNA + 1 strand
of newly synthesized DNA
⬇⬇⬇
because each strand of original DNA acts as a template for the new strand to be built
, Complementary base pairing rule of DNA ensures that the new strand is build as an
exact copy of the original one (AT-GC)
EVIDENCE FOR THE SEMI-CONSERVATIVE MODEL:
3 main DNA replication models
Semi-conservative → most widely believed → but there was no proof
for it
Meselson and Stahl → created experiment to prove it replicates
this way
They could differentiate between these theories by using:
- “Heavy” nitrogen isotope (15N)
DNA REPLICATION BASICS
DNA → in the nucleus of the cell → carries genetic information
↪ from the time we were a fertilized egg → every cell has had a
copy of it
Cell division occurs for:
- Growth → addition of new cells = make organism larger
- Repair of tissues through cell replacement
Each new cell requires a complete copy of the organism’s DNA → it
acquires it during DNA replication that occurs before cell
division (the only time)
Organism: from fertilized egg → large multicellular organism =
with an exact copy of the DNA
The same happens when repairing tissues:
New cells need to be produced →to replace those damaged or
destroyed
As wound heals → new cells are created to fill the place left in
the injury
↪ each an exact genetic copy
DNA of an organism → contains the instructions for that organism
↪ base sequences in it need to be copied exactly for new cells to
function properly
DNA in a cell → can be copied in 1 hour
SEMI-CONSERVATIVE NATURE OF DNA REPLICATION:
As one double strand of DNA is replicated → each new double strand
of DNA produced contains 1 strand of the original DNA + 1 strand
of newly synthesized DNA
⬇⬇⬇
because each strand of original DNA acts as a template for the new strand to be built
, Complementary base pairing rule of DNA ensures that the new strand is build as an
exact copy of the original one (AT-GC)
EVIDENCE FOR THE SEMI-CONSERVATIVE MODEL:
3 main DNA replication models
Semi-conservative → most widely believed → but there was no proof
for it
Meselson and Stahl → created experiment to prove it replicates
this way
They could differentiate between these theories by using:
- “Heavy” nitrogen isotope (15N)
