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Who’s Responsible?
 Rosalind Franklin took
diffraction x-ray
photographs of DNA
crystals
 In the 1950’s, Watson
& Crick built the first
model of DNA using
Franklin’s x-rays
 Nobel Peace Prize
awarded
DNA-Deoxyribonucleic
Acid
DNA is often called the blueprint
of life.
In simple terms, DNA contains the
instructions for making proteins
within the cell.
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Why do we study DNA?
We study DNA for
many reasons, e.g.,
its central
importance to all
life on Earth,
medical benefits
such as cures for
diseases and
better food crops.
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Chromosomes and DNA
Our genes
are on our
chromosomes.
Chromosomes
are made up
of a chemical
called DNA.
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SHAPE of DNA
DOUBLE HELIX
-two sided
-twisted
-ladder
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DNA Structure
Nucleotide: 3 components
1)Deoxyribose Sugar
2)Phosphate
3)Nitrogen Base
DNA is made of repeating
nucleotides
Nucleotide: monomer
DNA: polymer
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Four nitrogenous bases
DNA has four different bases:
C
Thymine T
Adenine A
Guanine G
The amount, the order
Cytosine
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Two Kinds of Bases in DNA
Pyrimidines are
single ring bases.
Purines are double
ring bases.
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Two Stranded DNA
Sides are called the
backbone: made of
alternating Phosphate
and Sugar
The ladder rungs: made
of paired nitrogen
bases.
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Hydrogen Bonds
The Bases connect by
Hydrogen Bonds
Hydrogen bonds are weak
but there are millions and
millions of them in a
single molecule of DNA.
The hydrogen bonds
between the bases are
shown here with dotted
lines
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Adenine and Thymine
always join together
A
T
Cytosine and Guanin
always join together
C
G
Pyrimidines and Purines
always pair together
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DNA by the Numbers
Each cell has about 2 m
of DNA.
The average human has
75 trillion cells.
The average human has
enough DNA to go from
the earth to the sun
more than 400 times.
DNA has a diameter of
only 0.000000002 m.
The earth is 150 billion m
or 93 million miles from
the sun.
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