CH7 key concepts genetic material: DNA DNA structure DNA replication
The discovery that DNA is the genetic code involved many ...
Transcript of The discovery that DNA is the genetic code involved many ...
The discovery that DNA is the genetic code involved many experiments.
Section 1: DNA: The Genetic Material
KWhat I Know
WWhat I Want to Find Out
LWhat I Learned
Essential Questions• Which experiments led to the discovery of DNA as the genetic material?• What is the basic structure of DNA?• What is the basic structure of eukaryotic chromosomes?
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Review• nucleic acid
New• double helix• nucleosome
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Vocabulary
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Discovery of the Genetic Material• After the rediscovery of Mendel’s work, scientist began to look for the
molecule involved in inheritance.
• For many years, scientists struggled to determine if DNA or protein was the source of genetic information.
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Discovery of the Genetic MaterialGriffith• First major experiment searching for the genetic material
• Involved transformation between two forms of S. pneumoniae
• Set the stage for the search to identify the transforming substance
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
Discovery of the Genetic MaterialAvery• Identified the molecule that transformed the R strain of S. pneumoniae into
the S strain
• Concluded that when the S cells were killed, DNA was released
• R bacteria incorporated this DNA into their cells and changed into S cells
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
Discovery of the Genetic Material Hershey and Chase• Used radioactive labeling to trace bacteriophage
DNA and protein.
• Concluded that the bacteriophage DNA was injected into the cell and provided the genetic information needed to produce new viruses.
Summary of Hershey-Chase ResultsInteractive Table
FPOAdd link to interactive table from page 328 (table 1) here.
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
DNA StructureNucleotides• Nucleotides are the subunits of nucleic acids, and consist of
• 5-carbon sugar
• Phosphate group
• Nitrogenous base
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
DNA StructureChargaff• Analyzed the amount of A, G, T,
and C in the DNA of various species
• Chargaff’s rule: C = G and T = A
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DNA StructureThe structure question• Search for the structure of DNA was lead by four scientists:
• Rosalind Franklin, British chemist
• Maurice Wilkins, British physicist
• Francis Crick, British physicist
• James Watson, American biologist
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
DNA StructureX-ray diffraction• X-ray diffraction techniques indicated that DNA was a double helix, or
twisted ladder shape.
• The double helix shape was formed by two strands of nucleotides twisted around each other.
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
DNA StructureWatson and Crick• Using Franklin and Chargaff’s data, Watson and Crick measured the
width of the helix and the spacing of the bases.
• They built a model that conformed the Franklin and Chargaff’s data.
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
DNA StructureDNA structure• DNA often is compared to a twisted ladder.
• Rails of the ladder are represented by the alternating deoxyribose and phosphate.
• The pairs of bases (cytosine-guanine or thymine-adenine) form the steps.
• Purine base always binds to a pyrimidine base
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
DNA StructureOrientation• DNA molecules have specific orientations of the two strands
• On the top rail, the strand is said to be oriented 5’ to 3’.• The strand on the bottom runs in the opposite direction and is
oriented 3’ to 5’.
Structure of DNA Animation
FPOAdd link to animation from page 331(Figure 8) here.
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
Chromosome Structure• In prokaryotes, DNA molecules are contained in the cytoplasm, and
consist mainly of a ring of DNA and associated proteins.
• In eukaryotes, DNA is organized into individual chromosomes.
DNA: The Genetic MaterialCopyright © McGraw-Hill Education
Chromosome Structure• To fit into a cell, DNA coils around a group of beadlike proteins called
histones.
• DNA + histones form a nucleosome, which group together into chromatin fibers, which supercoil to form a chromosome.