DNA
History
Function
Structure
Replication
History - Structure
Erwin Chargaff
– 1950’s Discovered that
the amount of A is
always equal to the
amount of T.
– The amount of C is
always equal to the
amount of G.
– What can be inferred?
• A goes with T
• G goes with C
– This became known as
Chargaff’s Rule
Rosalind Franklin
• 1950’s she used x-ray
diffraction to take a “photo”
of DNA.
Watson & Crick
•1953 Using their own
research and other the
created a model of DNA.
•DNA described as
Double Helix or twisted
ladder.
FUNCTION
Direct Cells Activities
• Genes, a segment of
DNA codes for a certain
protein.
• For example the Gene
for making Insulin
(protein) is coded for in a
section of DNA.
• The Gene has to be read
and pass on the
information to the
ribosome.
• DNA RNA PROTIEN
STRUCTURE
DNA is a double helix or a twisted ladder.
Both sides of the ladder are made of sugar
and phosphate.
The RUNGS (steps) are the bases
Rungs
Adenine pairs with Thymine
Cytosine pairs with Guanine
*They complement each other.
The bases are complementary, meaning
they fit together.
Only A with T and C with G.
MORE
BUILDING BLOCKS OF DNA.
DNA is like a puzzle where only
certain pieces of the puzzle fit
together.
Each puzzle piece is called
NUCLEOTIDE.
Each puzzle piece is made of a:
 SUGAR,
PHOSPHATE
NITROGEN BASE.
4 Bases
Adenine
Thymine
Cytosine
Guanine
Replication
oPurpose is to make an exact copy of
the DNA molecule.
o Why?
oSo during cell division (mitosis) each
new cell has an exact copy of the
original.
•STEPS OF REPLICATION:
1.Enzyme (polymerase) UNZIPS the
DNA at the weak hydrogen bonds.
2.Free floating nucleotides of DNA
BOND to the single strand by BASE
PAIRING.
3.Another enzyme rezips the two
chains together.
FINAL PRODUCT
A total of 4 strands in groups of two.