lectures 2 and 3 bb1035 c15.pptx
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Lectures 2 and 3 – DNA and heredity
Genes = unit of inheritanceWhat is the evidence that genes = DNA?
• cellular location• variation among species• present in right amounts
Robert Feulgen – DNA dye (1914)
Lectures 2 and 3 – DNA and heredity
Traits can be transferred:• 1928 Griffith & Streptococcus pneumoniae
nonvirulent virulent
What is the chemical nature of this heritable change?
Virulence (trait) transferred from one organism to another…
What is the evidence that Genes = DNA? Lectures 2 and 3 – DNA and heredity
• 1944 Avery - experimental system
DNA fulfills key properties of hereditary material
1. Create extract
2. Treat extract3. Add to R strain
4. Test for virulence
5. DNAse!
Take home = Gene comprised of DNA- concept of transformation…- traits can be transferred via DNA (transgenics)
• faithful duplication• informational content• variation
What is the evidence that Genes = DNA?
How?
Lectures 2 and 3 – DNA and heredity
What is DNA - “deoxyribonucleic acid”
(charge?)sugar
double ring
single ring
1. Pyrimidine content = purine content2. T = A; C=G3. applies to dsDNA -
(ssDNA, ssRNA, dsRNA?)
Chargaff’s rules
Lectures 2 and 3 – DNA and heredity
Heredity genes = DNA
Heredity requires DNA to be passed on fromgeneration to generation. Requires
• replication• segregation (mitosis/meiosis)• linked to cell cycle
karyokinesiscytokinesis
Lectures 2 and 3 – DNA and heredity
What are the molecular underpinnings of heredity?
How is DNA propagated? • antiparallel double stranded helix• hydrogen bonded base pairs• replication mechanism: strand separation
Faithful replication - molecular mechanism?
1st 2nd
Semiconservativereplication
Lectures 2 and 3 – DNA and heredity
How is DNA propagated ?
Semiconservativereplication Template strandGrowing strand
3 end
5 end
5 end
3 end
incoming ntcomplementarity
phosphodiester linkage
phosphate ions
Lectures 2 and 3 – DNA and heredity
How is DNA propagated ? SemiconservativereplicationProkaryotic
Circular chromosome - single origin
Circular chromosome - resolution
linear chromosome - no resolution
- telomere??
Rate of replication? Size of Genome?
1000nts/sec
4.7Mbs vs. 3.4GbsE. coli H. sapiens
Length of time to replicate genome? - 9.5 yrs to read genome (Hs) - 20-40 minutes replicate prokaryotic - Hs??? 50bp/sec, many ori’s
Topoisomerase
Eukaryotic
linear chromosome - multiple origins
Lectures 2 and 3 – DNA and heredity
How is DNA propagated ?Semiconservative
replication
Leading strand Parent DNA
OkazakifragmentLagging strand template
Leading strand template
Lagging strand35
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1. Helicase (H bonds)
RNAprimer
2. Primase
3. DNA Polymerase (III) + clamp (PCNA)4. DNA Polymerase (I)5. DNA Ligase
Telomere shortening!
Telomerase: RNA + protein
TTAGGG (2500X)
No Telomerase = 50-200bp/divisionCancer cells – telomerase!Stem Cells – telomerase!
Lectures 2 and 3 – DNA and heredity
How is DNA propagated?1. Replication2. Segregation3. Cytokinesis
EukaryoticMitosisMeiosis
ReproductionGrowth
Regeneration/Repair
ProkaryoticBinary Fission
Reproduction
Lectures 2 and 3 – DNA and heredity
How is DNA propagated?1. Replication2. Segregation3. Cytokinesis
Importance of cytoskeleton!
Lectures 2 and 3 – DNA and heredity
How is DNA propagated ?
Fidelity of replication: if 1/105 = 60,000 mutations/divisionHow prevent?
1. Proofreading – DNA Pol2. Mismatch repair3. Excision repair (ie. UV = Py dimers)
- mutations- increased incidence of cancer- <40% survive past 20yrs old
Biotechnology How might knowledge of replication be useful?
Leading strand Parent DNA
Lagging strand
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DNA sequencing
Polymerase Chain Reaction (amplify DNA)
Lectures 2 and 3 – DNA and heredity
DNA sequencing
Polymerase Chain Reaction (amplify DNA)1. template2. primer3. polymerase (thermostable - Archaea)4. ???
Biotechnology How might knowledge of replication be useful?
Applications
Lecture 3 – DNA and heredity
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