• Deoxyribonucleic acid (DNA)
– Stores info., copies itself
– Directs cell activities
– hereditary material passed from cell → cell
• Nucleic Acid – polymer;
monomer = nucleotide.
– two kinds: DNA and RNA.
Sections in a DNA mol.
called genes.
Genes code for proteins;
the hereditary info. in DNA
tells cell how to make
proteins
• Nucleotide:
three components
(CP: 230) (Hon: 197)
– 5 C sugar
– phosphate group
– nitrogenous base
(4 kinds in DNA)
• Nucleotide:
three components
(CP: 230) (Hon: 197)
– a 5-carbon sugar
– a phosphate group
– a nitrogenous base
(4 kinds in DNA)
Four Kinds of Nitrogenous Bases
• Pyrimidines - single ring
bases.
– Thymine and Cytosine
• Purines - double ring
bases.
N C
OC
N
O
CC
N
O C
N C
Thymine
– Adenine and Guanine
N C
C
C
N C
Cytosine
O
N
N C
• Base pairs
C
N C
C
(also called nucleotide pairs) C
N
N
are formed when a purine
N C
N C
bonds with a pyrimidine
Adenine N C Guanine N C
• A-T and C-G (always)
DNA STRUCTURE
• Shape is like twisted ladder.
• Called a double helix -two
strands bonded together &
twisted
– The bases form the rungs
of the ladder
• hydrogen bonds hold pairs
together; A-T, C-G
– Sugars and phosphates
form sides of ladder.
The
carbons
in the
sugar
are
labeled
DNA Animation
http://www.johnkyrk.com/DNAanatomy.html
http://207.207.4.198/pub/flash/24/menu.swf
Packaging DNA
• Eukaryotic DNA:
many levels of
packaging:
– Fundamental
unit is
Nucleosome –
• DNA wound
around proteins
called histones.
• (CP. 139)
• (Hon 151)
Nucleosome
Nucleosomes
• Nucleosomes
• Lowest DNA packaging
level
• Can be thought of as a
length of thread wound
around a spool, the thread
representing DNA and the
spool being histone
proteins.
DNA - By The Numbers!
• Each cell has about
2 meters (6 ft) of DNA.
• The average human has
60-75 trillion cells.
• Avg human has enough
DNA to go from the
Earth to the sun more
than 400 times.
• DNA has a diameter of
The earth is 150 billion meters
only 0.0000000002
or 93 million miles from
meters (20Ǻ)
the sun.
-10
[1Ǻ =10 m]
Karyotypes
• Normal
human male
karyotype
(the total set of
chrom. of an
organism)
Karyotypes
• Normal
human female
karyotype
The History of DNA
• Gregor Mendel-1866
– Determined “Unit characters” were the
method of passing on traits for inheritance
• Friedrich Meischer - 1868
– Studied nuclei of pus cells obtained from
discarded surgical bandages
– Detected a phosphorus-containing substance
that he named nuclein.
• Frederick Griffith 1928 : Work with
Bacteria
– Found that DNA taken from a virulent
(disease-causing) strain of bacteria
(Streptococcus pneumoniae)
– Transformed a non-virulent form of the
bacterium into a virulent form.
Oswald Avery, Colin MacLeod, and
Maclyn McCarty 1943
Continued the study of “Transformation”
principle
Mendel
Avery
Meischer
Griffith
MacLeod
McCarty
Transformation Of Bacteria
Two Strains Of Streptococcus
Capsule
Rough Strain
(Harmless)
Smooth Strain
w/Capsule
(Virulent)
Transformation Of Bacteria -Griffith’s Experiment
Smooth (virulent)
OUCH!
Control
Rough
Control
Control
Experimental
The History of DNA
• Alfred Hershey and Martha
Chase - 1952
– radioactive isotope tracer
experiment
– bacterial virus
(bacteriophage T2) infects
a host cell ( bacterium
Escherichia coli)
– found that T2 virus DNA,
not its protein coat, enters
the host cell
– genetic information for
replication of the virus
T 2 grown in
media
containing S35
incorporate S35
into their
proteins
Using S35
T2 attach to bacteria
and inject genetic
material
Bacteria grown
in normal nonradioactive
media
When centrifuged,
phage protein coats
remain in the
supernatant while
bacteria form a
pellet.
The
supernatant is
radioactive, but
the pellet is not.
Did protein enter the bacteria?
Blending causes phage
protein coat to fall off
Is protein the genetic material?
P32
T2 grown in
containing
media
incorporate P32
into their DNA
Using P32 Bacteria grown
T2 attach to bacteria
and inject genetic
material
in normal nonradioactive
media
When centrifuged,
phage protein coats
remain in the
supernatant while
bacteria form a
pellet
The pellet is
radioactive, but the
supernatant is not.
Did DNA enter the bacteria?
Blending causes phage
protein coat to fall off
Is DNA the genetic material?
The History of DNA Structure
• Erwin Chargaff- 1940 - “Chargaff’s rule”
– four bases may occur in varying proportions in
DNA of different organisms
– # of A = # of T, w/ two hydrogen bonds
–
= # of G and C are present w/ 3 hydrogen
bonds
• Rosalind Franklin and Maurice Wilkins
– X-ray diffraction study concluded DNA fibers
have two strands.
The History of DNA Structure
James Watson and Francis Crick University of Cambridge -1953
Worked on problem of making a DNA
molecule model that was double stranded but
also had the specific A - T and G - C base
equivalencies
Solution-double helical structure for DNA.
Franklin
Chargaff
Wilkins
Watson and Crick