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

35

35

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

35

35

35

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