Transcript DNA Lecture #1: DNA Structure and Proof That DNA Controls Traits

DNA: a history
DNA model
Double helix nebula
Griffith experiment: 1928
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A heat-killed lethal
strain of bacteria was
added to a non-lethal
strain. The non-lethal
strain was
transformed into a
lethal one.
1944: Avery: DNA is
the molecule involved.
DNA stores and
transmits genetic
information from one
generation to the next
non-lethal
lethal
heat-killed
lethal
transformed
Hershey-Chase experiment
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1952
Added radioactive
markers to the
proteins and DNA of
viruses
Only the tracers
attached to DNA
entered the bacteria.
The genetic material
of viruses is DNA
Components of DNA
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A long molecule made of chains of
nucleotides:
5-C sugar
 Phosphate
 Nitrogen-containing
bases
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One nucleotide group
4 Nitrogen bases
Ribose sugar
Adenine, Thymine, Cytosine
Guanine
Phosphate
DNA structure
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Chargaff’s rules: the
amount of
Adenine = Thymine
Cytosine = Guanine
1953: Watson and
Crick discover the
double helix structure
of DNA, where 2
strands wind around
each other
Watson and Crick’s original DNA model
Franklin’s X-ray diffraction of DNA
A twisted ladder
Rungs:
Bases held by H
bonds connect at
the center.
Sides:
 Sugar and
Phosphate
 Bases attach to the
ribose sugars
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Base pairing
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Hydrogen bonds
form between A and
T and between C
and G.
A fits with T
G fits with C
This explains
Chargaff’s rule
The Components and Structure of DNA
Copyright Pearson Prentice Hall
Hydrogen bonds form at the center of the rungs,
between the N base molecules
DNA has been found in every organism on
earth