BIOS E-1a Lecture 08 101711 annotated-1

BIOS E-1a Lecture 08 101711 annotated-1 - Lecture 8:...

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Lecture 8: Chromosome Theory Reading: Chapters 7, 9 (concepts 9.1 and 9.2) 1
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Genetic material must meet criteria: 1. Information 2. Replication 3. Transmission 4. Variation For fun, you might want to read some of the classic experiments: •G r i f f i t h Avery, MacLeod, and McCarty Hershey and Chase Franklin Watson and Crick Meselson and Stahl 2
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Levels of DNA structure 1. Nucleotides are the building blocks of DNA (and RNA). 2. A strand of DNA (or RNA) 3. Two strands form a double helix. 4. In living cells, DNA is associated with an array of different proteins to form chromosomes. 5. A genome is the complete complement of an organism’s genetic material. 3
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Nucleotides • 3 components –Phosphate group –Pentose sugar –Nitrogenous base 4
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• 3 components – Phosphate group – Pentose sugar • Deoxyribose – Nitrogenous base • Purines – adenine (A), guanine (G) • Pyrimidines – cytosine (C), thymine (T) 5
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RNA • 3 components – Phosphate group – Pentose sugar • Ribose – Nitrogenous base • Purines – adenine (A), guanine (G) • Pyrimidines – cytosine (C), uracil (U) 6
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• Conventional numbering system • Sugar carbons 1’ to 5’ • Base attached to 1’ • Phosphate attached to 5’ 7
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• Nucleotides covalently bonded • Phosphodiester bond: phosphate group links 2 sugars • Phosphates and sugars from backbone • Bases project from backbone • Directionality- 5’ to 3’ •5 T A C G 3 Strands 8
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• Amount of adenine similar to the amount of thymine and amount of cytosine similar to amount of guanine Base content in DNA from a variety of organisms 9
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•D N A i s – Double stranded – Helical – Sugar-phosphate backbone – Bases on the inside – Stabilized by hydrogen bonding – Base pairs with specific pairing 10
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• AT/GC or Chargoff’s rule – A pairs with T – G pairs with C – Keeps width consistent • 10 base pairs per turn • 2 DNA strands are complementary – 5’ – GCGGATTT – 3’ – 3’ – CGCCTAAA – 5’ • 2 strands are antiparallel – One strand 5’ to 3’ – Other stand 3’ to 5’ 11
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• Space-filling model shows grooves – Major groove • Where proteins bind and affect gene expression – Minor groove 12
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Semiconservative replication • During replication 2 parental strands separate and serve as template strands • New nucleotides must obey the AT/GC rule • End result 2 new double helices with same base sequence as original 13
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14
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• Origin of replication – Site of start point for replication • Bidirectional replication – Replication proceeds outward in opposite directions • Bacteria have a single origin • Eukaryotes require multiple origins 15
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DNA replication • Origin of replication provides an opening called a replication bubble that forms two replication forks • DNA replication proceeds outward from forks • Bacteria have single origin of replication • Eukaryotes have multiple origins of replication 16
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• DNA helicase – Binds to DNA and
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This note was uploaded on 02/09/2012 for the course BIOLOGY 102 taught by Professor Anderson during the Spring '11 term at Harvard.

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BIOS E-1a Lecture 08 101711 annotated-1 - Lecture 8:...

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