DNA double helix

Covers major portion of DNA structure, discovery, components and wide applications in today's life

1. Double Helical structure
of
DNA
Course Title: Food Biotechnology
B TECH FOOD
TECHNOLOGY
By
J Singh
R Gupta
A Singh
A Rehman
M P Tomar
H Srivastava
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2. Learning objectives:
• To get familiar with the term
DNA
• Discovery of DNA
• Contribution of major scientists
in the field of Nucleic acid
• Primary, Secondary and
Tertiary structures of DNA
• Applications and functions of
DNA
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3. DNA
• DNA - a polymer of deoxyribo
nucleotides
• found in chromosomes, mitochondria and
chloroplasts
• carries the genetic information
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4. DNA (Deoxyribo Nucleic
Acid): By Structure
DNA is a double stranded
molecule that is twisted into
a Helix (Spiraling staircase)
(Spiraling Staircase)
DNA Double Helix
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5. DNA: Major Contributions
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6. Rosalind Franklin
James Watson Francis Crick
Maurice Wilkins 6

7. Franklin’s Work
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8. In 1951 Rosalind Franklin discovers the Two Forms of DNA
through her X-ray diffraction images.
A – Dry Form B – Wet Form
Two forms of DNA
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9. Watson and Crick’s Work
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10. • 1951 James Watson traveled
from the United States to work
with Francis Crick at Cambridge
University
• Watson and Crick used the
“Model Building” approach
• They physically built models out
of wire, sheet metal, nuts and
bolts to come up with the
structure of DNA
Watson and Crick’s Work
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11. How Watson and Crick Solved the DNA Structure
• They already knew from Franklin and
Wilkins’ work that DNA was in the form of a
Double Helix
• They used
Chargaff’s Rule to
figure out how the 4
Bases match up in
pairs
Diagram representing X-ray diffraction
images
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12. How Watson and Crick Solved the DNA Structure
They discovered that:
• The Phosphate Backbone was on the outside
• Which protected the Bases on the inside
• DNA acts as a Template or a Copying Mechanism for
reproduction
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13. DNA Structure:
Achievements
Watson and Crick
alongwith Wilkins
won the Nobel Prize
in Physiology/
Medicine (1962) for
their discovery of
the DNA double
helix Structure.
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14. DNA Structure
•Primary
•Secondary
•Tertiary
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15. DNA Structure : Primary Structure
• Consists of a linear sequences of nucleotides.
linked together by phosphodiester bonds.
• Nucleotides consists of three components:
1. Nitrogenous base
Adenine
Guanine
Cytosine
Thymine (present in DNA only)
Uracil (present in RNA only)
2. 5-carbon sugar which is called deoxyribose (found
in DNA) and ribose (found in RNA).
3. One or more phosphate groups.

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16. Each strand consists of
1.Nitrogenous base
•Adenine ●Cytosine
•Guanine ●Thymine
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17. Each strand consists of:
2) A Sugar Phosphate backbone
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18. Each strand consists of:
1) Nitrogenous base
2. Sugar Phosphate Backbone
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19. DNA structure
• made up of molecules called nucleotides

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20. Components of a nucleotide
Base
Sugar
Phosphate
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21. 21

22. The secondary structure of
DNA
Two anti-parallel polynucleotide
chains wound around the same axis.
Sugar-phosphate chains wrap
around the periphery.
Bases (A, T, C and G) occupy the
core, forming complementary A · T
and G · C Watson-Crick base pairs.
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23.  hydrogen bonding;
 base stacking
The DNA double helix is held together
mainly by- Hydrogen bonds
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24. HYDROGEN BOND
• a chemical bond in which a hydrogen atom of
one molecule is attracted to an electronegative
atom, especially a nitrogen, oxygen, or fluorine
atom, usually of another molecule.
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25. Helical sense: right handed
Base pairs: almost
perpendicular to the helix
axis; 3.4 Å apart
One turn of the helix: 36
Å; ~10.4 base pairs
Minor groove: 12 Å across
Major groove: 22 Å across
Normally hydrated DNA: B-form DNA
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26. DNA Tertiary Structure
•DNA double helical
structure coils round
histones.
•Nucleosomes (10nm
fibres)
•Nucleosomes contain 146
nucleotides
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27. Applications of DNA
• Science and technology
have advanced since the
discovery in year 1953.
• Some achievements that
potentially became
successful due to its
invention.
Cloning
Genetically Modified
Foods (GMFs)
Genetic Engineering
DNA Fingerprinting/
Analysis
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28. Functions of DNA and
summary of structure
• DNA consists of four bases—A, G, C, and T—that are held in
linear array by phosphodiester bonds through the 3' and 5'
positions of adjacent deoxyribose moieties.
• DNA is organized into two strands by the pairing of bases A to T
and G to C on complementary strands. These strands form a
double helix around a central axis.
• The 3 x 10
9
base pairs of DNA in humans are organized into the
haploid complement of 23 chromosomes.
• DNA provides a template for its own replication and thus
maintenance of the genotype and for the transcription of the
roughly 30,000 human genes into a variety of RNA molecules.
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29. Thank You
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