powerlecture: chapter 13
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PowerLecture: Chapter 13. DNA Structure and Function. 13.1 The Hunt. Originally believed to be an unknown class of proteins Thinking was Heritable traits are diverse Molecules encoding traits must be diverse Proteins are made of 20 amino acids and are structurally diverse. - PowerPoint PPT PresentationTRANSCRIPT
PowerLecture:PowerLecture:Chapter 13Chapter 13
DNA Structure and FunctionDNA Structure and Function
13.1 The Hunt13.1 The Hunt
Originally believed to be an unknown Originally believed to be an unknown class of proteinsclass of proteins
Thinking wasThinking was Heritable traits are diverseHeritable traits are diverse Molecules encoding traits must be Molecules encoding traits must be
diversediverse Proteins are made of 20 amino acids Proteins are made of 20 amino acids
and are structurally diverseand are structurally diverse
Miescher Discovered DNAMiescher Discovered DNA
18681868 Johann Miescher investigated the chemical Johann Miescher investigated the chemical
composition of the nucleuscomposition of the nucleus Isolated an organic acid that was high in Isolated an organic acid that was high in
phosphorusphosphorus He called it nucleinHe called it nuclein
Griffith Discovers Griffith Discovers TransformationTransformation
19281928 Attempting to develop a vaccineAttempting to develop a vaccine Isolated two strains of Isolated two strains of Streptococcus Streptococcus
pneumoniaepneumoniae Rough strain was harmlessRough strain was harmless Smooth strain was pathogenicSmooth strain was pathogenic
TransformationTransformation
What happened in the fourth What happened in the fourth experiment?experiment?
The harmless R cells had been The harmless R cells had been transformedtransformed by material from the by material from the dead S cellsdead S cells
Descendents of the transformed cells Descendents of the transformed cells were also pathogenicwere also pathogenic
Avery, McCarty, and MacLeodAvery, McCarty, and MacLeodRepeated Griffith’s ExperimentRepeated Griffith’s Experiment
Oswald AveryOswald Avery Maclyn McCartyMaclyn McCarty Colin MacLeodColin MacLeod
Avery, McCarty, and MacLeodAdded the non-deadly Rough Type of Bacteria to the Heat-Killed Smooth
Type
CarbohydratesCarbohydrates LipidsLipids ProteinsProteins RNARNA DNADNA
To the Heat-Killed Smooth Type, To the Heat-Killed Smooth Type, added enzymes that added enzymes that
destroyed…destroyed…
S-Type Carbohydrates S-Type Carbohydrates DestroyedDestroyed
S-Type S-Type Lipids Lipids
DestroyedDestroyed
S-Type S-Type Proteins Proteins
DestroyedDestroyed
S-Type RNA S-Type RNA DestroyedDestroyed
S-Type DNA S-Type DNA DestroyedDestroyed
Conclusion:Conclusion:
DNA was the DNA was the transforming factor!transforming factor!
Oswald & AveryOswald & Avery
What is the transforming material?What is the transforming material? Cell extracts treated with protein-Cell extracts treated with protein-
digesting enzymes could still transform digesting enzymes could still transform bacteriabacteria
Cell extracts treated with DNA-digesting Cell extracts treated with DNA-digesting enzymes lost their transforming abilityenzymes lost their transforming ability
Concluded that DNA, not protein, Concluded that DNA, not protein, transforms bacteriatransforms bacteria
The Hershey-Chase The Hershey-Chase Experiment Experiment
Alfred Hershey Alfred Hershey & Martha & Martha
Chase worked Chase worked with a with a
bacteriophage:bacteriophage:
A virus that A virus that invades invades
bacteria. It bacteria. It consists of a consists of a
DNA coreDNA core and and a a protein coatprotein coat
DNADNA
Protein coatProtein coat
Protein coats of bacteriophages labeled with Sulfur-35Protein coats of bacteriophages labeled with Sulfur-35
DNA of bacteriophages labeled with Phosphorus-32DNA of bacteriophages labeled with Phosphorus-32
BacteriumBacterium
BacteriumBacterium
PhagePhage
PhagePhage1.1. Hershey and Chase mixed Hershey and Chase mixed
the radioactively-labeled the radioactively-labeled viruses with the bacteriaviruses with the bacteria
The viruses infect the The viruses infect the bacterial cells.bacterial cells.
Protein coats of bacteriophages labeled with Sulfur-35Protein coats of bacteriophages labeled with Sulfur-35
DNA of bacteriophages labeled with Phosphorus-32DNA of bacteriophages labeled with Phosphorus-32
1.1. Separated the viruses Separated the viruses from the bacteria by from the bacteria by agitating the virus-agitating the virus-bacteria mixture in a bacteria mixture in a blenderblender
Protein coats of bacteriophages labeled with Sulfur-35Protein coats of bacteriophages labeled with Sulfur-35
DNA of bacteriophages labeled with Phosphorus-32DNA of bacteriophages labeled with Phosphorus-32
1.1. Centrifuged the mixture so that the Centrifuged the mixture so that the bacteria would form a pellet at the bacteria would form a pellet at the bottom of the test tubebottom of the test tube
1.1. Measured the radioactivity in the pellet Measured the radioactivity in the pellet and in the liquidand in the liquid
Hershey & Chase’s Hershey & Chase’s ExperimentsExperiments
Created labeled bacteriophagesCreated labeled bacteriophages Radioactive sulfur Radioactive sulfur Radioactive phosphorus Radioactive phosphorus
Allowed labeled viruses to infect Allowed labeled viruses to infect bacteriabacteria
Asked: Where are the radioactive Asked: Where are the radioactive labels after infection?labels after infection?
virus particlelabeled with 35S
DNA (blue)being injected into bacterium
35S remainsoutside cells
virus particlelabeled with 32P
DNA (blue)being injected into bacterium
35P remainsinside cells
Fig. 13-4ab, p.209
Hershey and Chase ResultsHershey and Chase Results
Structure of the Structure of the Hereditary Hereditary MaterialMaterial
Experiments in the 1950s Experiments in the 1950s showed that DNA is the showed that DNA is the hereditary materialhereditary material
Scientists raced to Scientists raced to determine the structure of determine the structure of DNADNA
1953 - Watson and Crick 1953 - Watson and Crick proposed that DNA is a proposed that DNA is a double helixdouble helix
Figure 13.6Page 211
13.2 Structure of 13.2 Structure of Nucleotides Nucleotides
in DNAin DNA Each nucleotide consists ofEach nucleotide consists of
Deoxyribose (5-carbon sugar) Deoxyribose (5-carbon sugar)
Phosphate groupPhosphate group
A nitrogen-containing baseA nitrogen-containing base
Four basesFour bases Adenine, Guanine, Thymine, CytosineAdenine, Guanine, Thymine, Cytosine
Nucleotide BasesNucleotide Bases
phosphate group
deoxyribose
ADENINE (A)
THYMINE (T)
CYTOSINE (C)
GUANINE (G)
Composition of DNAComposition of DNA
Chargaff showed:Chargaff showed: Amount of adenine relative to guanine Amount of adenine relative to guanine
differs among speciesdiffers among species Amount of adenine always equals amount Amount of adenine always equals amount
of thymine and amount of guanine always of thymine and amount of guanine always
equals amount of cytosineequals amount of cytosine
A=T and G=CA=T and G=C
Rosalind Franklin’s WorkRosalind Franklin’s Work
Was an expert in X-ray Was an expert in X-ray crystallographycrystallography
Used this technique to examine Used this technique to examine DNA fibers DNA fibers
Concluded that DNA was some Concluded that DNA was some sort of helixsort of helix
Watson-Crick Watson-Crick ModelModel
DNA consists of two DNA consists of two
nucleotide strandsnucleotide strands
Strands run in opposite Strands run in opposite
directionsdirections
Strands are held Strands are held
together by hydrogen together by hydrogen
bonds between basesbonds between bases
A binds with T and C with A binds with T and C with
GG
Molecule is a double Molecule is a double
helixhelix
13.3 DNA Structure Helps 13.3 DNA Structure Helps Explain How It DuplicatesExplain How It Duplicates
DNA is two nucleotide strands held DNA is two nucleotide strands held
together by hydrogen bondstogether by hydrogen bonds
Hydrogen bonds between two Hydrogen bonds between two
strands are easily brokenstrands are easily broken
Each single strand then serves as Each single strand then serves as
template for new strandtemplate for new strand
How does DNA replicate?How does DNA replicate?
ConservativeConservative Semi-ConservativeSemi-Conservative DispersiveDispersive
Hypotheses:
• Bacteria cultured in medium Bacteria cultured in medium containing a containing a heavyheavy isotope of isotope of Nitrogen (Nitrogen (1515N)N)
Meselson-Stahl ExperimentMeselson-Stahl Experiment
• Bacteria transferred to a medium Bacteria transferred to a medium containing elemental Nitrogen containing elemental Nitrogen ((1414N)N)
Meselson-Stahl ExperimentMeselson-Stahl Experiment
Meselson-Stahl ExperimentMeselson-Stahl Experiment
1.1.DNA sample centrifuged after First DNA sample centrifuged after First replicationreplication
Meselson-Stahl ExperimentMeselson-Stahl Experiment
1.1.DNA sample centrifuged after DNA sample centrifuged after Second replicationSecond replication
DNA DNA ReplicatioReplicatio
nn Each parent Each parent
strand remains strand remains
intactintact
Every DNA Every DNA
molecule is half molecule is half
“old” and half “old” and half
“new”“new”Fig. 13-7, p.212
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 Energy for strand assembly is provided by removal of two provided by removal of two phosphate groups from free phosphate groups from free nucleotidesnucleotides
Fig. 13-8c, p.213
Strand AssemblyStrand Assembly
Continuous and Continuous and Discontinuous AssemblyDiscontinuous 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.
Base Pairing Base Pairing during during
ReplicationReplication
Each old Each old strand serves strand serves as the as the template for template for complementacomplementary new strandry new strand
Fig. 13-8, p. 213
Enzymes in ReplicationEnzymes in Replication
Enzymes unwind the two strands - helicaseEnzymes unwind the two strands - helicase DNA polymerase attaches complementary DNA polymerase attaches complementary
nucleotides nucleotides DNA ligase fills in gaps (Okazaki DNA ligase fills in gaps (Okazaki
fragments)fragments) Enzymes wind two strands togetherEnzymes wind two strands together
DNA RepairDNA Repair
Mistakes can occur during replicationMistakes can occur during replication DNA polymerase can read correct DNA polymerase can read correct
sequence from complementary sequence from complementary
strand and, together with DNA ligase, strand and, together with DNA ligase,
can repair mistakes in incorrect can repair mistakes in incorrect
strandstrand
13.4 Cloning13.4 Cloning
Making a genetically identical copy of Making a genetically identical copy of
an individualan individual Researchers have been creating Researchers have been creating
clones for decadesclones for decades These clones were created by These clones were created by
embryo splittingembryo splitting
1 A microneedle 2 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 sheepFig. 13-9, p.214
CloningCloning
Showed that differentiated cells Showed that differentiated cells
could be used to create clonescould be used to create clones Sheep udder cell was combined Sheep udder cell was combined
with enucleated egg cellwith enucleated egg cell Dolly is genetically identical to the Dolly is genetically identical to the
sheep that donated the udder cellsheep that donated the udder cell
Dolly: Dolly: Cloned from an Adult CellCloned from an Adult Cell
Fig. 13-9, p.214
Dolly: Cloned from an Adult Dolly: Cloned from an Adult CellCell
Ian Wilmut was the first to produce a Ian Wilmut was the first to produce a cloned sheep, which he named Dollycloned sheep, which he named Dolly
Dolly experienced health problems Dolly experienced health problems similar to other mammals cloned similar to other mammals cloned from adult DNAfrom adult DNA
Impacts, Issues: Impacts, Issues: Goodbye Goodbye DollyDolly
Fig. 13-1a, p.206
Goodbye DollyGoodbye Dolly
The risk of defects in clones is hugeThe risk of defects in clones is huge
Possible benefit – patients in desperate need of Possible benefit – patients in desperate need of organ transplantsorgan transplants
Genetically modified cloned animals may produce Genetically modified cloned animals may produce organs that human donors are less likely to rejectorgans that human donors are less likely to reject
Cloning humans – ethical?Cloning humans – ethical?
Impacts, Issues: Impacts, Issues: Goodbye Goodbye DollyDolly
Therapeutic CloningTherapeutic Cloning
SCNT – Somatic Cell Nuclear TransferSCNT – Somatic Cell Nuclear Transfer
Transplant DNA of a somatic cell Transplant DNA of a somatic cell from the heart, liver, muscles, or from the heart, liver, muscles, or nerves into a stem cell nerves into a stem cell (undifferentiated cell)(undifferentiated cell)
More ClonesMore Clones
http://www.cyagra.com/gallery/jewel.htm
CowsCows
http://www.popsci.com/scitech/article/2003-05/face-should-we-clone-fading-species
Fig. 13-10, p.215