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Biol321 Molecular Genetics

Handout 3

Transcription generates two units

P lacI

LacI

P lac O

DNALacZ LacY LacA

mRNAUnit 1 Unit 2

Repressor -Galactosidase Permease Trans-acetylaseMolecular

Genetics&Genomics

CT CTNT NT recA lexA

CT CTNT NT SOS genes

CT CTNT NT

CTNT

OFFlow expression

OFFlow expression

OFFlow expression

Dr. Fahd M. Nasr

Sixth EditionSeptember 2006

Department of Biology Faculty of SciencesLebanese University Hadath-Beirut Lebanon

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Structure of eukaryotic genes and chromosomesStructure of eukaryotic genes and chromosomes

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11nm fiber

Solenoid model for packaging of nucleosomes into the 30-nm chromatin fiber

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Organization of 30-nm chromatin fiber into looped domains

H3/H4 tetramer

H2A/H2B dimer

H2A/H2B dimer

H2A/H2B dimer

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Electron micrograph of a metaphase chromosome depleted of histonesThe chromosome maintains its general shape by a nonhistoneprotein scaffold from which loops of DNA protrude

Sizes of eukaryotic genomes

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The mountain grasshopper Podisma pedestris

The fruit flyDrosophila melanogaster

18,000 Mb 180 Mb

C-value paradox

C-value paradox: complexity does not correlate with genome size

3.4 x 109 bpHomo sapiens

6.7 x 1011 bpAmoeba dubia

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N-value paradox: complexity does not correlate with gene number

~25,000 genes~25,000 genes ~26,000 genes~26,000 genes ~50,000 genes~50,000 genes

2Myrmecia pilosula (An ant)

8Drosophila melanogaster (Fruit fly)10Arabidopsis thaliana (Plant in the mustard family)12Caenorhabditis elegans (Microscopic roundworm)

32Saccharomyces cerevisiae (Budding yeast)36Xenopus laevis (South African clawed frog)38Felis catus (Cat)

40Mus musculus (House mouse)46Homo sapiens (Human)54Ovis aries (Sheep)

60Bos taurus, B. indicus (Cattle)62E. asinus (Donkey)64Equus caballus (Horse)

78Canis familiaris (Domestic dog)1260Ophioglossum reticulatum (A fern)

diploid number of chromosomesSpecies

Chromosomes numbers in different species

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Cohesins along chromosome arms are

released

Cohesinremain s at centromere

Cohesin at centromer is degraded

The alignment of sister chromatids via cohesin

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R-banding patterns

G Banding Pattern

1q22.3

550 bands

650 bands

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Fluorescence in situ hybridization (FISH)

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A B

C

D E

F G

Chromosome painting (or spectral karyotyping)

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There are three distinct domains of life

Last Common Universal Ancestor

LUCA

Pyrococcus fumari (113ºC)

The Three-Domain System

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Extremophiles (Archea)Thermophiles Halophiles

Methanogens

Cryophiles

Anatomy of prokaryotic genomes

• Most with a genome size < 5Mb• Genomes varies widely ranging from

0.58Mb in Mycoplasma genitalium to 9.2Mb in Myxococcus xanthus

• Most of the bacterial genomes are circular and haploid

• Some exceptions to this traditional view start to emerge

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Examples of genome organization in prokaryotes

Examples of genome organization in prokaryotes

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Total genome schematic of Borrelia burgdorferi

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E. coli genome Nucleoid condensed dscccDNA

Histone-like proteinsNegatively supercoiled

• Endosymbiotic theory– Mito and chloroplast free living bacteria

• Ploidy– Nucleus 2n– Organelles polyploid

Rat mito. 2-10 copies/organelle~1000 organelles/cell

up to 10,000 organelle genomes

Eukaryote genome