Unit2-1Students - Review of Unit 1-2 1 Physical structure...

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1. What holds the DNA duplex together Hydrogen bonds Hydrophobic interactions Van der Waals interactions Ionic interactions 1. DNA denaturation High temperature Low salt Basic conditions (high pH) Organic solvents 1. Physical structure of DNA Chargaff Wilkins and Franklin Watson and Crick Review of Unit 1-2
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5. Eukaryotic genomes are highly complex, and contain unique, moderately repetitive and highly repetitive sequences 6. Genes are mainly in the single copy regions of the genome 4. Renaturation kinetics can be used to estimate genome size and complexity 7. Genome size does not always correlate with organism complexity: C-value paradox Review of Unit 1-2
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Unit 2: DNA Replication Reading: Weaver pp. 639-682   More detail in the reading than you need to know – Focus on what is covered in lectures
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DNA RNA Protein Protein synthesis (translation) RNA synthesis (transcription) DNA replication CENTRAL DOGMA
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Replication: the general process A new strand is synthesized using the existing denatured DNA strands as a template Uses complementary base pairing, and requires a series of enzymes Highly regulated process
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Why study replication? After DNA is replicated the genetic information is passed on to daughter cells. Although this is a highly regulated process, mistakes in copying can and do occur. Mistakes in genes that regulate the cell cycle can cause a cell to lose control over its replication. Cancer cells are examples of cells lacking cell-cycle control!
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Questions about DNA Replication Do old DNA strands pair with new or old DNA? How and where does replication begin? What proteins are required for DNA synthesis? Does replication go in one direction or bidirectionally?
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Questions About DNA Replication Do old DNA strands pair with new or old DNA? The double helix structure suggests a mode of replication: the two strands separate and each serves as a template for a new complementary strand to be synthesized Other possibilities existed, so this had to be tested experimentally
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Dispersive Possible Mechanisms Of Replication old old and new mixed Semiconservative 1. Conservative new
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Conservative Possible Mechanisms Of Replication new old Semiconservative old and new mixed 2. Dispersive
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Dispersive Conservative Possible Mechanisms Of Replication new old old and new mixed 3. Semiconservative
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Meselson and Stahl tested these models experimentally 1. Grew bacteria in the presence of 15 N “heavy” nitrogen [“Normal” nitrogen has atomic mass of 14.008 ( 14 N)] 1. The E. coli bacteria incorporate 15 N into DNA 3. 15 N-labeled DNA can be distinguished from DNA containing 14 N by density-gradient centrifugation
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centrifugation (100,000X g) CsCl forms a gradient Least dense Most dense 15 N + CsCl DNA will reach and remain at the location within the gradient that shares its density Density-gradient centrifugation 14 N + CsCl 15 N 14 N
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15 N 14 N 90 min 30 min Bacteria replicate ~ every 30 minutes Heavy Light 14 N 15 N
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Unit2-1Students - Review of Unit 1-2 1 Physical structure...

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