Download DNA the Genetic Material

DNA the Genetic Material
Big Picture
• For most of the last century, no one knew
what Mendel’s “factors” were.
• Sutton first developed chromosomal theory
in 1902, but only circumstantial evidence
that factors were genes on chromosomes.
This is a story...
• About the process of science, as well as the
structure and function of DNA.
• 14.1 What is the genetic material?
The Hammerling Experiment: Cells Store
Hereditary Information in the Nucleus
Joachim Hammerling discovered that
hereditary information in Acetabularia
(unicellular green alga) resided in the foot
region, which is also the location of the
nucleus.
• (p. 280) How did he know?
• By amputating differerent areas, grafting to
other alga, and seeing what parts would
grow.
• The form that was found in the foot region is
the one that would influence new growth.
• Transplantation Experiments: Each
Cell Contains a Full Set of Genetic
Instructions
Later experiments in the mid-1950s
showed that the nucleus of eukaryotic
cells includes a full set of genetic
information. (p. 281)
• By transplanting nuclei from one frog
species into that of another.
• Totipotent- nucleus of adult cell carries
instructions to create entire organism,
• The Griffith Experiment: Hereditary
Information Can Pass Between Organisms
• 1928
Frederick Griffith - (p. 282)
• Non-pathogenic S. pneumoniae was
transformed by dead pathogenic S.
pneumoniae. Information specifiying the
virulent surface protein had been delivered to
the safe live form.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mixture of heat-killed
pathogenic and live
Live nonpathogenic
nonpathogenic strains
strain of S. pneumoniae
of S. pneumoniae
Live pathogenic
Heat-killed pathogenic
strain of S. pneumoniae
strain of S. pneumoniae
+
Polysaccharide
coat
(1)
Mice die
(2)
Mice live
(3)
Mice live
(4)
Mice die; their blood
contains live pathogenic
strain of S. pneumoniae
• The Avery and Hershey-Chase
Experiments: The Active Principle Is
DNA
•
1944- Oswald Avery provided
conclusive evidence that DNA is the
heredity material for the bacterial
specimens under investigation. (p. 283)
• He removed as much protein and other
material as possible, but still non
pathogenic cells were transformed, so
not protein, fat, or carb.
• Alfred Hershey and Martha Chase - (p. 283)
• Bacteriophage: simple nucleic acid with
protein coat.
• Identified DNA by marking phosporous with
32P
• Identified protein by marking sulfur with 35S.
• Found that it was the DNA, marked with 32P,
that was injected into the bacteria to cause
disease.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Protein coat labeled
with 35S
DNA labeled with 32P
bacteriophages
Fig.T2
14.5(TE
are labeled with Art)
radioactive isotopes.
Bacteriophages infect
bacterial cells.
Bacterial cells are agitated
to remove protein coats.
35S
radioactivity
found in the medium
32P
radioactivity found
in the bacterial cells
• 14.2 What is the structure of DNA?
The Chemical Nature of Nucleic
Acids
Both DNA and RNA are formed of
nucleotides joined together in series.
Each nucleotide is composed of a fivecarbon sugar, a phosphate group, and a
nitrogen-containing base. (p. 284)
Chargaff's Rule - there are always equal
proportions of purines and pyrimidines. (p.
285)
•
•
A-T
G-C
•
Pure AGgie. (purines are A & G)
• Do you remember how we numbered carbons
in sugar?
• Start from right side.
• Base attached to 1’, phosphate attached to 5’.
This comes up when we talk about
replication, transcription, and translation. (We
read from 5’ to 3’)
• Phosphodiester bond between nucleotides.
• The Three-Dimensional Structure of
DNA
Rosalyn Franklin was able to obtain the
first glimpse of DNA using X-ray
diffraction in 1953, while Watson and
Crick theorized that DNA exists in a
double-helical, antiparallel configuration.
(pp. 286-287)
• Famous example of woman being scr’d.
• Could you guess the pattern by looking
at the x-ray?
• 14.3 How does DNA replicate?
The Meselson-Stahl Experiment:
DNA Replication Is Semiconservative
Matthew Meselson and Franklin Stahl
demonstrated that DNA replication is
semiconservative because each strand
of the original duplex becomes one of
the two strands in each new duplex. (p.
288)
• Also figured out by using isotopes, this
time 14N.
• What would the F1 generation look like
if completely new DNA were
synthesized, rather than semiconservative?
• It would be heavy as in test tube #2 in
diagram.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Control group
(unlabeled DNA)
1
2
4. The DNA was suspended
in a cesium chloride
solution.
Centrifugation
F1 generation DNA
(one heavy/light hybrid
molecule)
3
4
Labeled parent
DNA (both strands
heavy)
F2 generation DNA
(one unlabeled molecule,
one heavy/light hybrid
molecule)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
PO4
Base
5 CH2
O
1
4
3
OH
2
• The Replication Process
Replication of E. coli begins at a
specific origin, proceeds bidirectionally,
and ends at a specific terminus. (p. 290)
• OriC is beginning point.
• Contains many A-T pairs, which are
double bonded, easy to open.
• Leading and lagging strand, why so
named?
• One side is synthesized continuously,
but the other limited to short segments
(Okizaki fragments).
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
39
DNA
polymerase III
Leading
strand
DNA double helix
Okazaki
fragment
Lagging strand
Primer
59
• DNA primase -creates a short RNA
primer complementary to a DNA
template;
• DNA helicase, which unwinds the helix
DNA polymerase, which then
synthesizes new DNA by adding
nucleotides to the growing strands; and
DNA ligase, which creates
phosphodiester bonds between
adjacent Okazaki fragments. (pp. 292293)
• Each of these has a name that gives away its
job.
•
These are the only enzymes you are responsible for.
• Replication fork- Open area of DNA
where replication takes place.
Replication can be divided into three
stages: initiation, elongation, and
termination. (p. 294)
• Initiation- there are two OriC’s, one on
each strand.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Leading
strand
First subunit of
DNA polymerase III
Okazaki RNA
fragment primer
Lagging
strand
Single-strand binding proteins
Parental
DNA helix
Helicase
Primase
Second subunit of
DNA polymerase III
DNA ligase
DNA polymerase I
• Eukaryotic DNA Replication
The major difference between
prokaryotic and eukaryotic replication is
that eukaryotic chromosomes have
multiple replication origins, whereas
prokaryotic chromosomes have a single
point of origin. (p. 295)
•
14.4 What is a gene?
The One-Gene/One-Polypeptide
Hypothesis
Beadle and Tatum concluded that
genes produce their effects by
specifying the structure of enzymes,
and that each gene encodes the
structure of one enzyme. Today, this is
commonly referred to as the onegene/one-polypeptide relationship. (p.
297)
• How did they figure this out?
• Using bread mold nutrient mutantsmutants that lack the ability to make a
certain aa, and must be supplied with it
to grow.
• Found that each enzyme that was
disabled corresponded to a defect in a
specific gene.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
X rays or ultraviolet light
Wild-type
Neurospora
Asexual
spores
Minimal
medium
Products of
one meiosis
Select one of
the spores
Test on minimal
medium to confirm
presence of mutation
Growth on
complete
medium
Meiosis
Grow on
complete medium
Minimal media supplemented with:
Choline
Pyridoxine
Riboflavin
Minimal
Nucleic
Arginine
Niacin
control
Inositol acid Folic
p-Amino
Thiamine
acid
benzoic acid
• How DNA Encodes Protein Structure
• Sanger sequenced the amino acids of
insulin, first time to sequence a protein.
Then Ingram found that a single aa
substitution Valine instead of Glutamic
acid, caused sickle cell anemia.
The question is answered
Over 50 years of research has
yielded clear evidence that DNA is
the molecule responsible for the
inheritance of traits from one
generation to the next, and that
DNA is divided into functional
subunits, or genes, located on
chromosomes. (p. 298)