2. A HISTORY OF DNA
• Discovery of the DNA double helix
A. Frederick Griffith – Discovers that a factor
in diseased bacteria can transform harmless
bacteria into deadly bacteria
(1928)
B. Rosalind Franklin - X-ray photo of DNA.
(1952)
C. Watson and Crick - described the
DNA molecule from Franklin’s X-ray.
(1953)
3. Watson & Crick proposed…
•DNA had specific pairing between the
nitrogen bases:
ADENINE – THYMINE
CYTOSINE - GUANINE
•DNA was made of 2 long stands of
nucleotides arranged in a specific way
called the “Complementary Rule”
4. DNA Double Helix
“Rungs of ladder”
Nitrogenous
Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone
5. Genetic material of cells…
• GENES – units of genetic material that
CODES FOR A SPECIFIC TRAIT
• Called NUCLEIC ACIDS
• DNA is made up of repeating molecules
called NUCLEOTIDES
9. Chargaff’s Rule
• Adenine must pair with Thymine
• Guanine must pair with Cytosine
• Their amounts in a given DNA molecule will be
about the same.
same
T
A
G
C
13. The Code of Life…
• The “code” of the chromosome is the
SPECIFIC ORDER that bases occur.
A T C G T A T G C G G…
14. DNA Replication
• DNA must be copied
• The DNA molecule produces 2
IDENTICAL new complementary
strands following the rules of
base pairing:
A-T, G-C
•Each strand of the
original DNA serves as
a template for the new
strand
15. DNA Replication
• Semi-conservative
Model:
1. Watson and Crick
showed: the two strands of
the parental molecule
separate, and each
functions as a template for
synthesis of a new
complementary strand.
.
Parental DNA
DNA Template
New DNA
16. (1961)
Watson & Crick proposed…
• …DNA controlled cell function by
serving as a template for PROTEIN
structure.
• 3 Nucleotides = a triplet or CODON
(which code for a specific AMINO ACID)
• AMINO ACIDS are the building blocks
of proteins.
17. DNA Transcription
• DNA can “unzip”
itself and RNA
nucleotides match
up to the DNA
strand.
• Both DNA & RNA
are formed from
NUCLEOTIDES and
are called NUCLEIC
acids.
19. AMAZING DNA FACTS…
• DNA from a single human
cell extends in a single
thread for almost 2 meters
long!!!
• It contains information
equal to some 600,000
printed pages of 500 words
each!!!
(a library of about 1,000 books)