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II. INTERNAL ORGANIZATION OF EUKARYOTIC CELLS

II. INTERNAL ORGANIZATION OF EUKARYOTIC CELLS. Structure of a „typical” animal cell. Structure of a „typical” plant cell. II.1.4. Nucleus. Biological significance : storage, expression and transmission of the genetic information. Segmented nuclei of leukocytes. neutrophils.

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II. INTERNAL ORGANIZATION OF EUKARYOTIC CELLS

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  1. II. INTERNAL ORGANIZATION OF EUKARYOTIC CELLS

  2. Structure of a „typical” animal cell

  3. Structure of a „typical” plant cell

  4. II.1.4. Nucleus Biological significance: storage, expression and transmission of the genetic information.

  5. Segmented nuclei of leukocytes neutrophils

  6. Structural components

  7. II.1.4.1. Nuclear membrane (envelope) cytoplasm nuclear membrane nuclear lamina chromatin nuclear pore Biological significance: limiting layer between the inner part of the nucleus and the cytoplasm. Specific transport of micro- and macromolecules.

  8. The nuclear envelope is formed from two concentric membranes that are continuous with the endoplasmic reticulum (ER). The space between the two membranes is the perinuclear space which is continuous with the lumen of the ER. The inner nuclear membrane contains proteins which enable it to bind to the nuclear lamina (network of intermediate filaments), which binds the chromatin. The double-membrane envelope is penetrated by nuclear pores.

  9. Nuclear pore Construction surface wiev side wiev EM image

  10. Relationship of the nucleus and the cytosol

  11. The chromatin is composed of deoxyribonucleic acids and proteins. In interphase they are arranged in a relatively loose , „network” form. EM shows that there are two different forms of the chromatin, one appearing as a light element (euchromatin), the other one being dark (heterochromatin). II.1.4.2. Chromatin Euchromatin: Here the chromatin is loosely arranged. The DNA double helices are partially split to single strands by RNA polymerases. Heterochromatin: Closely packed chromatin . The DNA is organized by histon and non-histone proteins.

  12. Euchromatic nucleus of neuron

  13. Structure 1. Level of organisation: Nucleosome H2A, H2B, H3 and H4 (two molecules of each) are building the Histone-Octamer . The DNA double helix makes two turns around this octamer (166 base pairs). H1 binds to theis complex. (packing level: 6-7x) Octamer H1 The chromatin is a DNA-protein complex About half of the chromatin is protein: they are either histones or non-histone proteins. Histones are small, positively charged proteins, which bind non-specifically to DNA end compensate the negative charge of phosphate groups of the DNA. Histone classes: H1, H2A, H2B, H3 and H4.

  14. 2. Level of organisation : 30 nm chromatin fiber The nucleosomes are spirally organized around the H1 core (packing level: ~ 40 x) This structure is broken to segments by binding of non-histone proteins (e.g. gene regulator proteins).

  15. 3. Level of organisation: 300 nm chromatin fibers 20 000-30 000 base pairs 30 nm chromatin fiber loop domains 300 nm

  16. Chromosomes W. Waldeyer, 1888: " …thick chromatin structureswhich can be seen during mitosis and meiosis...„ Name:chroma: colorand soma: body Boveri and Sutton, 1905. Chromosome theory: the chromoses are the carriers of the genetic information.. Chromosomes exists only during cell division as microscopically detecteble units. At the start of the mitosis (M phase) each chromose has replicated and consists of two sister chromatids joined together

  17. Fine structure Chromatids: 300 nm chromatin fiber form spirals (packing level: 10 000 x) 700 nm 300 nm

  18. Staining of the chromosomes • Fluorescent stains (e.g. Quinacrin): Q-bands specific for AT-rich DNA regions • Giemsa-staining:according to the technique applied, either G-bands ("Giemsa-positiv") specific for AT-rich DNA-regions or R-bands ("Giemsa-negativ") specific for GC-rich DNA-regions

  19. Chromosomes The human karyotype

  20. Chromosomal organization of different species baker’s yeast 32 corn 20 rice 24 wheat 42 tobacco 48 fruitfly 8 house fly 12 ant 48 frog 26 carp 104 dog 38 cat 64 mouse 40 rat 42 cattle 60 rhesus monkey 42 human 46

  21. Variability in chromosomal organization. Chromosomal organization (karyotype) can show high variability even in closely related species. Reeves deer The number of genes is equal! Indian deer

  22. Structure of the chromosomes Te l o mer shorter arm „p” centromer longer arm „q” sister chromatids X 4 5 Scanning-EM, human chromosomes Schematic view of chromosomal regions 2 5 1 4 1 1 3 2 1 1 1 1 2 2 2 3 3

  23. Telomers, aging, cancer (and Dolly) Human telomer: 15 000 base pairs of repeated TTAGGG DNA sequences. Shortening: 50-200 base pairs/division. In germline cells: telomere terminal transferase (telomerase): ribonucleoprotein reverse transcriptase.

  24. Binding of the chromosomes to the mitotic spindle Attachment site: kinetochor at the centromer

  25. Preparation of chromosomes, karyotype determination Blood culture (phytohaemagglutinin) colchicin separation of erythrocytes and white blood cells fixation staining microphoto arrange according to size, centromer position and banding pattern

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