Office hr:5-6 Thr Geisel S&E Office hr:5-6 Thr Office hr:10-11am Wed ROMA cafe Works for everyone? 1

A cell is an organism or a unit of a multi-cellular organism 2

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Lecture 1 Genetic Information and the Cell Nucleus 4

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Several genomes of model system organisms have been sequenced Mouse! Zebrafish? 7

Mitochondria and chloroplasts contain their own genetic information 1.5 billion years ago 8

Many cell types, one genome: differentiation 9

The cells we have in our bodies are “wimpy” compared to protists 10

Karyotype Chromosome painting Different states of chromosomes throughout the life of a cell 11

Three DNA sequences required to produce a Chromosome: 1. 2 Telomeres (replication and prevent sticking) 2. Centromere (Kinetochore) (attaching daughter chromosomes) 3. 2 replication origins 12

Nucleosomes as seen in EM 30 nm thickUnfold into beads on a string DNA (string) and nucleosome core particles (beads) 13

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The Zigzag model 30 nm fibers are often interrupted by sequence- specific DNA- binding proteins 15

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Covalent modification of core histone tails 18

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Lampbrush chromosomes are interphase chromosomes in oocytes with active transcription Stiff extended chromatin loops 20

An RNA processing protein is shown green 21

Actively expressed Not expressed DNA from organisms that usually do not produce lampbrush chromosome is packaged into lampbrush chromosomes-- maybe all are in loop forms but are smaller 22

Interphase chromosomes in insects-multiple cycles of DNA synthesis without cell division 23

Bands (95%) and interbands (5%). Both have genes. Bands do not correlate with genes. Some bands have multiple genes and some lack genes Three times more genes than Bands Different levels of gene expression: Higher at interbands. Heterogeneity of chromosomes (dynamic) 24

Chromosome puffs 5 puffs 22 hours 25

RNA synthesis in chromosome puffs Polytene chromosomes from C. tentans New RNA in red BrUTP Older RNA in blue 3 H-uridine EM Autoradiograph 26

Heterochromatin--no expression 10%, additional levels of packing of 30-nm fibers. Commonly found around centromeres, near telomeres, other positions. Not “dead” DNA but has important functions; Euchromatin-- interphase chromosomes, looped 30-nm Fibers. 27

Individual chromosomes occupy discrete territories in an interphase nucleus- not intertwined! By nuclear matrix or scaffold? 28

Chromosome regions that are close to nuclear envelope 29

Replication forks Helicase topoisomerase 30

Visualizing transcription (rRNA) RNA polymerase 31

Nucleolus is a ribosome-producing factory 32

txn assembly 33

Nucleoli dissociate and fuse 34

Subnuclear structures: Nucleoli, Cajal bodies, GEMS, Interchromatin Granule clusters Or speckles, Fibrillarin (sno RNP) Pre-mRNA splicing Chromatin 35

Ribosomes on ER 37

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Dosage compensation Barr body 41

Covalent modification of DNA 42

CpG islands--methylation inactivates transcription 43

Summary 1.Eukaryotic cells keep genetic information in DNA enclosed in cell nucleus and mitochondria and chloroplasts (plants); 2.The genomes of several model organisms are completely sequenced; 3.Long DNA molecules are efficiently packed in chromosomes; 4.Cell nucleus is a highly organized structure; 5.Different sets of genes are expressed in different tissues; 6.Epigenetic regulation of gene expression. 44