2. WHAT HAPPENS WITH THE DNA
IN THE CELLS?
Before cell division: DNA must
replicate
During cell growth the cell
needs to produce proteins!
The informations for proteins
is IN the DNA
GENE - POLYPEPTIDE

3. POSSIBLE MODELS FOR DNA
REPLICATION

4. In 1958 Meselsohn and Stahl, in America carried out a simple
experiment to show that DNA replication was semi conservative.
N15
N14
DNA of bacteria greowing in
a medium of heavy N15 DNA of bacteria
grown in N15
and replicated
ONCE in N14
DNA of bacteria
grown in N15 and
replicated TWICE in
N14

5. RESULTS OF THE EXPERIMENT
Which is your conclusion?
What would you expect to happen if they kept the bacteria for one more
generation in N14?

6. DNA
SEMICONSERVATIVE REPLICATION
1.- DNA unwinds. The
double helix shape is
lost.
2.- DNA unzips. The
hydrogen bonds
holding the strands
together are broken.
The two strands
separate.
3.- Activated
nucleotides (with
two extra
phosphates) are
attracted to their
complementary
bases in the
strands that serve
as moulds.
4.-
Hydrogen
bonds
between
bases are
formed (2
between A-
T and three
between C-
G)
5.- ENZYME DNA
POLYMERASE
produces the covalent
bonds between the
phosphate and the
sugar to form each of
the strands.
6.- Daughter helixes
separate one from the
other.

7. Animacion replication