PowerLecture: Chapter 13 DNA Structure and Function Slide 2 13.1
The Hunt Originally believed to be an unknown class of proteins
Originally believed to be an unknown class of proteins Thinking was
Thinking was Heritable traits are diverse Heritable traits are
diverse Molecules encoding traits must be diverse Molecules
encoding traits must be diverse Proteins are made of 20 amino acids
and are structurally diverse Proteins are made of 20 amino acids
and are structurally diverse Slide 3 Miescher Discovered DNA 1868
1868 Johann Miescher investigated the chemical composition of the
nucleus Johann Miescher investigated the chemical composition of
the nucleus Isolated an organic acid that was high in phosphorus
Isolated an organic acid that was high in phosphorus He called it
nuclein He called it nuclein Slide 4 Griffith Discovers
Transformation 1928 1928 Attempting to develop a vaccine Attempting
to develop a vaccine Isolated two strains of Streptococcus
pneumoniae Isolated two strains of Streptococcus pneumoniae Rough
strain was harmless Rough strain was harmless Smooth strain was
pathogenic Smooth strain was pathogenic Slide 5 Slide 6
Transformation What happened in the fourth experiment? What
happened in the fourth experiment? The harmless R cells had been
transformed by material from the dead S cells The harmless R cells
had been transformed by material from the dead S cells Descendents
of the transformed cells were also pathogenic Descendents of the
transformed cells were also pathogenic Slide 7 Avery, McCarty, and
MacLeod Repeated Griffiths Experiment Oswald Avery Maclyn McCarty
Colin MacLeod Slide 8 Avery, McCarty, and MacLeod Added the
non-deadly Rough Type of Bacteria to the Heat-Killed Smooth
TypeCarbohydratesLipidsProteinsRNADNA To the Heat-Killed Smooth
Type, added enzymes that destroyed Slide 9 S-Type Carbohydrates
Destroyed S-Type Lipids Destroyed S-Type Proteins Destroyed S-Type
RNA Destroyed S-Type DNA Destroyed Conclusion: DNA was the
transforming factor! Slide 10 Oswald & Avery What is the
transforming material? What is the transforming material? Cell
extracts treated with protein-digesting enzymes could still
transform bacteria Cell extracts treated with protein-digesting
enzymes could still transform bacteria Cell extracts treated with
DNA-digesting enzymes lost their transforming ability Cell extracts
treated with DNA-digesting enzymes lost their transforming ability
Concluded that DNA, not protein, transforms bacteria Concluded that
DNA, not protein, transforms bacteria Slide 11 The Hershey-Chase
Experiment Alfred Hershey & Martha Chase worked with a
bacteriophage: A virus that invades bacteria. It consists of a DNA
core and a protein coat DNA Protein coat Slide 12 Protein coats of
bacteriophages labeled with Sulfur-35 DNA of bacteriophages labeled
with Phosphorus-32 Bacterium Bacterium Phage Phage 1.Hershey and
Chase mixed the radioactively-labeled viruses with the bacteria The
viruses infect the bacterial cells. Slide 13 Protein coats of
bacteriophages labeled with Sulfur-35 DNA of bacteriophages labeled
with Phosphorus-32 1.Separated the viruses from the bacteria by
agitating the virus-bacteria mixture in a blender Slide 14 Protein
coats of bacteriophages labeled with Sulfur-35 DNA of
bacteriophages labeled with Phosphorus-32 1.Centrifuged the mixture
so that the bacteria would form a pellet at the bottom of the test
tube 1.Measured the radioactivity in the pellet and in the liquid
Slide 15 Hershey & Chases Experiments Created labeled
bacteriophages Created labeled bacteriophages Radioactive sulfur
Radioactive sulfur Radioactive phosphorus Radioactive phosphorus
Allowed labeled viruses to infect bacteria Allowed labeled viruses
to infect bacteria Asked: Where are the radioactive labels after
infection? Asked: Where are the radioactive labels after infection?
Slide 16 virus particle labeled with 35 S DNA (blue) being injected
into bacterium 35 S remains outside cells virus particle labeled
with 32 P DNA (blue) being injected into bacterium 35 P remains
inside cells Fig. 13-4ab, p.209 Hershey and Chase Results Slide 17
Structure of the Hereditary Material Experiments in the 1950s
showed that DNA is the hereditary material Experiments in the 1950s
showed that DNA is the hereditary material Scientists raced to
determine the structure of DNA Scientists raced to determine the
structure of DNA 1953 - Watson and Crick proposed that DNA is a
double helix 1953 - Watson and Crick proposed that DNA is a double
helix Figure 13.6 Page 211 Slide 18 13.2 Structure of Nucleotides
in DNA Each nucleotide consists of Each nucleotide consists of
Deoxyribose (5-carbon sugar) Deoxyribose (5-carbon sugar) Phosphate
group Phosphate group A nitrogen-containing base A
nitrogen-containing base Four bases Four bases Adenine, Guanine,
Thymine, Cytosine Adenine, Guanine, Thymine, Cytosine Slide 19
Nucleotide Bases phosphate group deoxyribose ADENINE (A) THYMINE
(T) CYTOSINE (C) GUANINE (G) Slide 20 Composition of DNA Chargaff
showed: Chargaff showed: Amount of adenine relative to guanine
differs among species Amount of adenine relative to guanine differs
among species Amount of adenine always equals amount of thymine and
amount of guanine always equals amount of cytosine Amount of
adenine always equals amount of thymine and amount of guanine
always equals amount of cytosine A=T and G=C Slide 21 Rosalind
Franklins Work Was an expert in X-ray crystallography Was an expert
in X-ray crystallography Used this technique to examine DNA fibers
Used this technique to examine DNA fibers Concluded that DNA was
some sort of helix Concluded that DNA was some sort of helix Slide
22 Watson-Crick Model DNA consists of two nucleotide strands DNA
consists of two nucleotide strands Strands run in opposite
directions Strands run in opposite directions Strands are held
together by hydrogen bonds between bases Strands are held together
by hydrogen bonds between bases A binds with T and C with G A binds
with T and C with G Molecule is a double helix Molecule is a double
helix Slide 23 13.3 DNA Structure Helps Explain How It Duplicates
DNA is two nucleotide strands held together by hydrogen bonds DNA
is two nucleotide strands held together by hydrogen bonds Hydrogen
bonds between two strands are easily broken Hydrogen bonds between
two strands are easily broken Each single strand then serves as
template for new strand Each single strand then serves as template
for new strand Slide 24 How does DNA replicate?
ConservativeSemi-ConservativeDispersive Hypotheses: Slide 25
Bacteria cultured in medium containing a heavy isotope of Nitrogen
( 15 N)Bacteria cultured in medium containing a heavy isotope of
Nitrogen ( 15 N) Meselson-Stahl Experiment Slide 26 Bacteria
transferred to a medium containing elemental Nitrogen ( 14
N)Bacteria transferred to a medium containing elemental Nitrogen (
14 N) Meselson-Stahl Experiment Slide 27 1.DNA sample centrifuged
after First replication Slide 28 Meselson-Stahl Experiment 1.DNA
sample centrifuged after Second replication Slide 29 DNA
Replication Each parent strand remains intact Each parent strand
remains intact Every DNA molecule is half old and half new Every
DNA molecule is half old and half new Fig. 13-7, p.212 Slide 30 Why
the discontinuous additions? Nucleotides can only be joined to an
exposed OH group that is attached to the 3 carbon of a growing
strand. Energy for strand assembly is provided by removal of two
phosphate groups from free nucleotides Fig. 13-8c, p.213 Strand
Assembly Slide 31 Continuous and Discontinuous Assembly Strands can
only be assembled in the 5 to 3 direction continuous on just one
parent strand. This is because DNA synthesis occurs only in the 5
to 3 direction. discontinuous: short, separate stretches of
nucleotides are added to the template, and then ligase fill in the
gaps between them. Slide 32 Base Pairing during Replication Each
old strand serves as the template for complementary new strand Fig.
13-8, p. 213 Slide 33 Enzymes in Replication Enzymes unwind the two
strands - helicase Enzymes unwind the two strands - helicase DNA
polymerase attaches complementary nucleotides DNA polymerase
attaches complementary nucleotides DNA ligase fills in gaps
(Okazaki fragments) DNA ligase fills in gaps (Okazaki fragments)
Enzymes wind two strands together Enzymes wind two strands together
Slide 34 DNA Repair Mistakes can occur during replication Mistakes
can occur during replication DNA polymerase can read correct
sequence from complementary strand and, together with DNA ligase,
can repair mistakes in incorrect strand DNA polymerase can read
correct sequence from complementary strand and, together with DNA
ligase, can repair mistakes in incorrect strand Slide 35 13.4
Cloning Making a genetically identical copy of an individual Making
a genetically identical copy of an individual Researchers have been
creating clones for decades Researchers have been creating clones
for decades These clones were created by embryo splitting These
clones were created by embryo splitting Slide 36 1 A microneedle2
The microneedle has emptied the sheep egg of its own nucleus. 3 DNA
from a donor cell is about to be deposited in the enucleated egg. 4
An electric spark will stimulate the egg to enter mitotic cell
division. the first cloned sheep Fig. 13-9, p.214Cloning Slide 37
Showed that differentiated cells could be used to create clones
Showed that differentiated cells could be used to create clones
Sheep udder cell was combined with enucleated egg cell Sheep udder
cell was combined with enucleated egg cell Dolly is genetically
identical to the sheep that donated the udder cell Dolly is
genetically identical to the sheep that donated the udder cell
Dolly: Cloned from an Adult Cell Slide 38 Fig. 13-9, p.214 Dolly:
Cloned from an Adult Cell Slide 39 Ian Wilmut was the first to
produce a cloned sheep, which he named Dolly Ian Wilmut was the
first to produce a cloned sheep, which he named Dolly Dolly
experienced health problems similar to other mammals cloned from
adult DNA Dolly experienced health problems similar to other
mammals cloned from adult DNA Impacts, Issues: Goodbye Dolly Slide
40 Fig. 13-1a, p.206 Goodbye Dolly Slide 41 The risk of defects in
clones is huge The risk of defects in clones is huge Possible
benefit patients in desperate need of organ transplants Possible
benefit patients in desperate need of organ transplants Genetically
modified cloned animals may produce organs that human donors are
less likely to reject Genetically modified cloned animals may
produce organs that human donors are less likely to reject Cloning
humans ethical? Cloning humans ethical? Impacts, Issues: Goodbye
Dolly Slide 42 Slide 43 Therapeutic Cloning SCNT Somatic Cell
Nuclear Transfer SCNT Somatic Cell Nuclear Transfer Transplant DNA
of a somatic cell from the heart, liver, muscles, or nerves into a
stem cell (undifferentiated cell) Transplant DNA of a somatic cell
from the heart, liver, muscles, or nerves into a stem cell
(undifferentiated cell) Slide 44 More Clones
http://www.cyagra.com/gallery/jewel.htm Cows
http://www.popsci.com/scitech/article/2003-05/face-should-we-clone-fading-species
Slide 45 Fig. 13-10, p.215
