DNA

1. DNA
(Deoxyribonucleic Acid)

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

6. DNA Nucleotide
Phosphate
Group
O
O=P-O
O
5
CH2
O
N
C
1
C4
Sugar
(deoxyribose)
C3
C2
Nitrogenous base
(A, G, C, or T)

7. DNA Double Helix
5
O
3
3
P
5
O
O
C
G
1
P
5
3
2
4
4
2
3
P
1
T
5
A
P
3
O
O
P
5
O
3
5
P

8. Nitrogenous Bases
• PURINES
1. Adenine (A)
2. Guanine (G)
A or G
• PYRIMIDINES
3. Thymine (T)
4. Cytosine (C)
T or C

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

10. BASE-PAIRINGS
H-bonds
G
C
T
A

11. DNA is wrapped tightly around
histones and coiled tightly to form
chromosomes

12. Functions
Genetic Diversity…
• Different
arrangements of
NUCLEOTIDES in a
nucleic acid (DNA)
provides the key to
DIVERSITY among
living organisms.

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.

18. DNA Translation
• The cell uses
information from
“messenger” RNA
to produce proteins

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)

20. RNA

21. Subdivisions
• mRNA –
messenger RNA
• rRNA - ribosomal
RNA
• tRNA – transfer
RNA

22. Thank you