Chapter 9 and some of 8 DNA and the Molecular Structure of Chromosomes

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Chapter 9 and some of 8DNA and the Molecular
Structure of Chromosomes
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Chapter Outline

• Functions of the Genetic Material
• Proof That Genetic Information Is Stored in DNA
• The Structures of DNA and RNA
• Chromosome Structure in Prokaryotes and Viruses

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Functions of the Genetic Material

• The genetic material must replicate, control the
  growth and development of the organism, and allow
  the organism to adapt to changes in the
  environment.

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Functions of the Genetic Material

• Genotypic Function Replication
• Phenotypic Function Gene Expression
• Evolutionary Allows for Mutation

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Chromosomes

• Genes are located on chromosomes.
• Chromosomes contain proteins and nucleic acids.
• The nucleic acids are deoxyribonucleic acid (DNA)
  and ribonucleic acid (RNA).

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Proof that Genetic Information is Stored in DNA

• In most organisms, the genetic information is
  encoded in DNA. In some viruses, RNA Is the
  genetic material. Viroids are infectious naked
  RNA molecules, and prions are infectious,
  heritable proteins (not TRUE).

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DNA Mediates Transformation
Convert IIR to IIIS By DNA?
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Avery MacLeod and McCarty Experiment
Circa 1943
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The Genetic Material of Bacteriophage T2 is DNA
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The Genetic Material of Tobacco Mosaic Virus is
RNA
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Viroids and Prions

• Viroids are infectious, naked RNA molecules.
• Prions are heritable (What do they mean here?),
  infectious proteins that do not contain nucleic
  acids.

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Key Points

• The genetic information of most living organisms
  is stored in deoxyribonucleic acid (DNA).
• In some viruses, the genetic information is
  present in ribonucleic acid (RNA).
• Viroids and prions are infectious naked molecules
  of RNA and protein, respectively.

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The Structures ofDNA and RNA

• DNA is usually double-stranded, with adenine
  paired with thymine and guanine paired with
  cytosine. RNA is usually single-stranded and
  contains uracil in place of thymine.

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nucleotide sugar base phosphate
nucleoside sugar base
When Do we Find RNA Mixed with The DNA?
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Ribonucleotide Reductase
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Pyrimidines have the longer name and smaller
base Purines have the shorter name and bigger base
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Structure of aPolynucleotide Chain
Why do we Always talk about DNA going in the 5
to 3 direction?
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Deoxyribonucleotides
What is dideoxyadenosine triphosphate (ddATP)?
Why are dideoxynucleotides useful in Mol.Bio.?
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One of Chargaffs Rules
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X-ray Diffraction Pattern of DNA
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The Double Helix
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I hate when DNA is not depicted properly!
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DNA Structure

• Complementary Base Pairs (A with T, G with C
• Antiparallel Strands
• Right-handed double helix (B-DNA)
• (No obvious reason to me why Right-handed is
  better than left-handed)

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A-DNA, B-DNA and Z-DNA
The Z-DNA helix is left-handed and has a
structure that repeats every 2 base pairs. The
major and minor grooves, unlike A- and B-DNA,
show little difference in width
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A-DNA, B-DNA and Z-DNA
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Supercoiling(higher order structure)
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What circular DNA exists in humans?
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Key Points

• DNA usually exists as a double helix, with the
  two strands held together by hydrogen bonds
  between the complementary base pairs adenine
  paired with thymine and guanine paired with
  cytosine.
• The complementarity of the two strands of a
  double helix makes DNA uniquely suited to store
  and transmit genetic information.

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Key Points

• The two strands of a DNA double helix have
  opposite chemical polarity.
• RNA usually exists as a single-stranded HELIX
  containing uracil instead of thymine.
• Why Does RNA form a helical structure?

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STACKING OF BASES
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The DNA of Prokaryotes and Viruses

• Prokaryotes are monoploid.
• Most viruses and prokaryotes have a single set of
  genes stored in a single chromosome, which
  contains a single molecule of nucleic acid.

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The E. coli Chromosome
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Key Points

• The DNA molecules in prokaryotic and viral
  chromosomes are organized into negatively
  supercoiled domains.
• Bacterial chromosomes contain circular molecules
  of DNA segregated into about 50 domains.

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The Genetics of Bacteria

• Bacteria contain genes that mutate to produce
  altered phenotypes. Gene transfer in bacteria is
  unidirectionalfrom donor cells to recipient
  cells.

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Bacteria

• One main chromosome with a few thousand genes.
• Variable number of plasmids and episomes.
• Asexual reproduction by simple fission.

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Recombination in Bacteria
Does this recombination process interfere with
DNA cloning experiments?
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Key Points

• Bacteria usually contain one main chromosome.
• Wild-type bacteria are prototrophs they can
  synthesize everything they need to grow and
  reproduce given an energy source and some
  inorganic molecules.
• Auxotrophic mutant bacteria require additional
  metabolites for growth.

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Key Points

• Gene transfer in bacteria is unidirectional
  genes from a donor cell are transferred to a
  recipient cell, with no transfer from recipient
  to donor.

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Mechanisms of Genetic Exchange in Bacteria

• Bacteria exchange genetic material through three
  different parasexual processes.

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Transformation inBacillus subtilis (NOT TRUE for
E.Coli)
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Streptococcus pneumoniae Phenotypes
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Transformation-Griffiths Expt
1928