copyright © 2010 pearson education inc. lecture 05 - dna structure based on chapter 2 - dna: the...
TRANSCRIPT
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Copyright © 2010 Pearson Education Inc.
Lecture 05 - DNAStructureBased on Chapter 2 - DNA: The Genetic Material
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1. The Search for the Genetic Material
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2. Griffith’s Transformation Experiment
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3. Avery’s Transformation Experiment
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Avery Experiment
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4. Hershey and Chase’s Bacteriophage Experiment
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Hershey Chase Experiment
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5. RNA as Viral Genetic Material
• All known cellular organisms and many viruses have DNA as their genetic material. Some viruses, however, use RNA instead.
• Examples of RNA viruses include:– Bacteriophages such as MS2 and Qb.– Animal viruses such as poliovirus and human
immunodeficiency virus (HIV).– Plant viruses such as tobacco mosaic virus (TMV)
and barley yellow dwarf virus.
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6a. The Composition and Structure of DNA and RNA
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6b. The Composition and Structure of DNA and RNA
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6c. The Composition and Structure of DNA and RNA
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6d. The Composition and Structure of DNA and RNA
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6e. The Composition and Structure of DNA and RNA
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7a. The DNA Double Helix
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7b. The DNA Double Helix
Chargaff’s Rules –
From inspection of data such as that shown in Table 2.2. above Erwin Chargaff concluded that:
• the amount of purine always equals the amount of pyrimidine
• the amount of G equals C, and the amount of A equals T
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7c. The DNA Double Helix
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7d. The DNA Double Helix
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7e. The DNA Double Helix
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8. RNA Structure
Similarities and differences between DNA and RNA structure:
• RNA structure is very similar to that of DNA.• It is a polymer of ribonucleotides (the sugar is ribose
rather than deoxyribose).• Three of its bases are the same (A, G, and C) while it
contains U rather than T.• Functional RNA in a cell is single-stranded, but internal
base pairing can produce secondary structure in the molecule.
• Some viruses use either dsRNA or ssRNA for their genomes. Double-stranded RNA is structurally very similar to dsDNA.
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9. The Organization of DNA in Chromosomes
• Cellular DNA is organized into chromosomes. • A genome is the chromosome or set of
chromosomes that contains all the DNA of an organism.
• In prokaryotes the genome is usually a single circular chromosome.
• In eukaryotes, the genome is one complete
haploid set of nuclear chromosomes. Mitochondrial and sometimes chloroplast DNA are also present.
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10a. Prokaryotic Chromosomes
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10b. Prokaryotic Chromosomes
DNA Supercoiling
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10c. Prokaryotic Chromosomes
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11. Eukaryotic Chromosomes
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12a. The Structure of Chromatin
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12b. The Structure of Chromatin
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12c. The Structure of Chromatin
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13. Euchromatin and Heterochromatin
• The cell cycle affects DNA packing, with DNA condensing for mitosis and meiosis and then decondensing during interphase, being most dispersed at S phase.
• Staining of chromatin reveals two forms:– Euchromatin condenses and decondenses with the
cell cycle. Euchromatin accounts for most of the genome in active cells.
– Heterochromatin remains condensed throughout the cell cycle. There are two types based on activity:
• Constitutive heterochromatin• Facultative heterochromatin varies between cell
types or developmental stages
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14. Unique- and Repetitive-Sequence DNA
• Sequences vary widely in how often they occur within a genome. The categories are:– Unique-sequence DNA, present in one or a few copies.– Moderately repetitive DNA, present in a few to 105
copies.– Highly repetitive DNA, present in about 105–107 copies.
• Prokaryotes - mostly unique-sequence DNA• Eukaryotes have a mix of unique and repetitive sequences.
– Unique-sequence DNA includes most of the genes that encode proteins.
– Human DNA contains about 65% unique sequences.– Repetitive-sequence DNA includes the moderately and
highly repeated sequences. They may be dispersed throughout the genome or clustered in tandem repeats.