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DNA
Deoxyribonucleic Acid
Purpose
• DNA codes for
proteins and is the
blueprint for life.
• The same DNA is
found in all cells in
your body (sex cells
have half of the DNA)!
• Only certain parts of
the DNA molecule are
read and used in
each cell type.
DNA and Chromosomes
• Prokaryotes
– DNA in circular form
called “plasmid”
– E. Coli has over 4.6
million base pairs!
• Eukaryotes
– Linear DNA in form of
chromosome
– Human cells contain
about 3 billion base
pairs!
Chromosome Composition
• A Nucleosome
is DNA tightly
wound around
protein spheres
called
“histones”
• Nucleosomes
supercoil and
become thick fiber
of chromosomes
• Nucleosomes play
role in gene
regulation –
turning off and on
genes
Structure
• Discovered by
Watson and
Crick in 1953
• Shaped like a
twisted ladder
called a “double
helix”
Rosalind Franklin
• Used X-Ray
diffraction to get
information about the
structure of DNA:
Chargaff’s rules
• The relative amounts of adenine and
thymine are the same in DNA
• The relative amounts of cytosine and
guanine are the same.
Nucleotide
• Subunit of DNA
• made up of a
sugar,
phosphate and
one nitrogen
base.
What makes up the sides of
DNA Ladder?
1. Deoxyribose
sugar
2. Phosphate
group
• Run in opposite
directions called
“anti-parallel”
• Important when
copying DNA
• Run in direction
5’-3’
Nitrogen bases make up Rungs
Purines
Pyrimidines
(double ring)
(single ring)
Adenine-------(double H bond)--------Thymine
Guanine-------(triple H bond)---------Cytosine
Putting it all together
• The order of
bases in DNA
makes you
different from
the person
sitting next to
you!