DNA; from discovery to structure and functions.

1. D ISC OVERY A N D STR U C TU R E
DEOXYRIBO NUCLEIC ACID
(DNA)
11/9/2017 Dr.Asif Mir

2. P R O T E I N M A K I N G M A C H I N E RY
DNA IS ALSO KNOWN AS THE BLUEPRINT OF LIFE.

3. DISCOVERY OF DNA
The discovery of DNA Double Helix is one of the greatest
findings of all time, but it’s also one of the most
controversial

4. The search for the secret of life dates back nearly a century
prior to Watson and Crick’s ground breaking discovery in
1953
1865 1909 1911 195019441929

5. Gregor Mendel
Introduces the concept of heredity
1865 1909 1911 1929 1944 1950

6. Wilhelm Johannsen
Coins the term “Gene”
1865 1909 1911 1929 1944 1950

7. Thomas Hunt Morgan
Discovers that genes are responsible for inheritance
1865 1909 1911 1929 1944 1950

8. Phoebus Levene
Discovers that DNA is made up of
nucleotides, phosphates, sugars and 4 bases
1865 1909 1911 1929 1944 1950

9. Oswald Avery:
Shows that DNA can transform the property of cells
1865 1909 1911 1929 1944 1950
However, this idea was not
universally accepted

10. Erwin Chargaff:
Shows that: A + G = T + C = 50%
1865 1909 1911 1929 1944 1950
Chargaff’s Rule is an important equation in the
discovery of the structure of DNA

11. SECRET OF LIFE : DNA
• Rosalind Franklin took pictures using X-Rays in the
1930’s

12. James Watson & Francis
Crick discovered double
helix structure of DNA in
1953 using Fanklin’s
pictures.

13. In 1962 Watson, Crick & Wilkins won the Nobel Prize for their discovery of
the structure of DNA
The Nobel Prize
However, there is no mention of Franklin’s key work.

14. STRUCTURE OF DNA
• DNA is a polymer.
• The monomer of DNA is
called a nucleotide.
• Nucleotides linked
together to form the sides
of the DNA molecule.
• DNA molecule has shape
of a double helix.
• The sides are anti-
parallel.

15. WHAT’S IN ITS NAME?
• One 5 carbon sugar called
deoxyribose.
• “Deoxy” = one less oxygen.
• “ribo” = than ribose.
• Deoxyribonucleic acid
• “nucleic” = found in
nucleus.
• “acid” = acidic Deoxyribose, a pentose sugar,
has each carbon numbered.

16. 16
ONE STRAND OF DNA
• The backbone of the
molecule is alternating
phosphates and
deoxyribose sugar
• The teeth are
nitrogenous bases.
phosphate
deoxyribose
bases

18. 18
FOUR NITROGENOUS BASES
• Cytosine C
• Thymine T
• Adenine A
• Guanine G
DNA has four different bases:

19. 19
TWO KINDS OF BASES IN DNA
• Pyrimidines are
single ring bases.
• Purines are double
ring bases.
C
C
C
C
N
N
O
N
C
C
C
C
N
N
N
N
N
C

20. 20
THYMINE AND CYTOSINE ARE
PYRIMIDINES
• Thymine and cytosine each have one ring of carbon
and nitrogen atoms.
C
C
C
C
N
N
O
N
Cytosine
C
C
C
C
N
N
O
O
Thymine
C

21. 21
ADENINE AND GUANINE ARE PURINES
• Adenine and guanine each have two rings of
carbon and nitrogen atoms.
C
C
C
C
N
N
N
Adenine
N
N
C
C
C
C
C
N
N
O
N
Guanine
N
N
C

22. 22
TWO STRANDED DNA
• Remember, DNA has
two strands that fit
together something like
a zipper.
• The teeth are the
nitrogenous bases but
why do they stick
together?

23. 23
C
C
C
C
N
N
O
N
C
C
C
C
N
N
O
N
N
N
C
HYDROGEN BONDS
• The bases attract each other
because of hydrogen bonds.
• Hydrogen bonds are weak
but there are millions and
millions of them in a single
molecule of DNA.
• The bonds between cytosine
and guanine are shown here
with dotted lines

24. 24
HYDROGEN BONDS, CONT.
• When making
hydrogen bonds,
cytosine always pairs
up with guanine
• Adenine always pairs
up with thymine
• Adenine is bonded to
thymine here
C
C
C
C
N
N
O
O
C

25. DNA APPLICATIONS
• Cloning
• Recombinant DNA technology
• Forensics like fingerprinting
• Genetic Engineering
• DNA profiling
• Medical diagnosis
• Agricultural applications
• Human and animal therapeutics