Download The Structure of DNA DNA Has the Structure of a Winding Staircase

The Structure of DNA
DNA Has the Structure of a Winding
Staircase
• Early 1950’s, James
Watson and Francis
Crick determined that
DNA is a molecule
that is a double helix.
• A double helix is two
strands twisted
around each other.
• Each strand is
composed of
nucleotides.
• Nucleotides are the
subunits that make up
DNA.
• Made of 3 parts:
phosphate group,
deoxyribose (sugar) &
a nitrogen base.
Nucleotide Components
1.
2.
3.
Deoxyribose- The five
carbon sugar in DNA.
Forms the full name of
DNA (deoxyribonucleic
acid).
Phosphate Groupalternates with
deoxyribose to form the
sides of the “ladder”.
Nitrogen basesAdenine (A), Thymine
(T), Cytosine (C), &
Guanine (G).
Chargaff’s Observations
• In 1949, Erwin Chargaff’s data showed
that for each organism he studied, the
amount of adenine always equaled the
amount of thymine.
• And, the amount of cytosine always
equaled the amount of guanine.
DNA Model
• In 1952, Watson &
Crick determined the
structure of DNA with
the help of data
collected by Rosalind
Franklin and
Chargaff.
Base-Pairing Rules
• Adenine forms 2
hydrogen bonds with
Thymine
• Cytosine forms 3
hydrogen bonds with
Guanine
• The hydrogen bonds
between the nitrogen
bases keep the two
strands of DNA
together.
• Each strand is
complementary to the
other. Ex. TCGAACT is
complementary to
AGCTTGA