II. INTERNAL ORGANIZATION OF EUKARYOTIC CELLS. Structure of a „typical” animal cell.
-
Upload
elwin-johnston -
Category
Documents
-
view
224 -
download
0
Transcript of II. INTERNAL ORGANIZATION OF EUKARYOTIC CELLS. Structure of a „typical” animal cell.
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 leukocytesSegmented nuclei of leukocytes
neutrophils
Structural components
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.
The nuclear envelopenuclear envelope is formed from two concentric membranes that are continuous with the endoplasmic reticulum (ER). The space between the two membranes is the perinuclear spaceperinuclear space which is continuous with the lumen of the ER.
The inner nuclear membrane contains proteins which enable it to bind to the nuclear laminanuclear lamina (network of intermediate filaments), which binds the chromatin.
The double-membrane envelope is penetrated by nuclear poresnuclear pores.
Nuclear pore
EM imageConstruction
surface wiev
side wiev
Relationship of the nucleus and the cytosol
II.1.4.2. Chromatin
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).
HeterochromatinHeterochromatin: Closely packed chromatin . The DNA is organized by histon and non-histone proteins.
Euchromatin:Euchromatin:
Here the chromatin is loosely arranged. The DNA double helices are partially split to single strands by RNA polymerases.
Euchromatic nucleus of neuronEuchromatic nucleus of neuron
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) H1
Octamer
1. Level of organisation: NucleosomeNucleosome
Structure
The chromatin is a DNA-protein complex About half of the chromatin is protein: they are either histones or non-histone proteins.
Histones 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.
2. Level of organisation : 30 nm chromatin fiber30 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).
3. Level of organisation: 300 nm chromatin fibers300 nm chromatin fibers
30 nm chromatin fiber
loop domains
20 000-30 000 base pairs
300
nm
Chromosomes
W. Waldeyer, 1888:
" …thick chromatin structures which can be seen during mitosis and meiosis...„
Name: chroma: color and 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 Chromosomes exists only during cell division as microscopically detecteble units. detecteble units.
At the start of the mitosis (M phase) each chromose has replicated and consists of two sister chromatids joined together
Fine structure
Chromatids: 300 nm chromatin fiber form spirals (packing level: 10 000 x)
300 nm
700 nm
Staining of the chromosomes
• Fluorescent stains (e.g. Quinacrin): Q-Q-bands bands specific for AT-rich DNA regions
• Giemsa-staining:according to the technique applied, either G-bandsG-bands ("Giemsa-positiv")
specific for AT-rich DNA-regions or
R-bandsR-bands ("Giemsa-negativ")
specific for GC-rich DNA-regions
ChromosomesThe human karyotype
fruitfly 8 house fly 12 ant 48 frog 26 carp 104 dog 38 cat 64 mouse
40 rat42
cattle 60 rhesus monkey 42 human 46
baker’s yeast 32 corn
20 rice 24 wheat
42 tobacco 48
Chromosomal organization of different species
Variability in chromosomal organization.
Chromosomal organization (karyotype) can show high variability even in closely related species.
The number of genes is equal!
Reeves deer
Indian deer
Scanning-EM, human
chromosomes
Schematic view of
chromosomal regions
X 4 5
Tel omer
shorter arm „p”
longer arm „q”
centromer1
23
45
1
1 1
111
2
2
2 233
sister chromatids
Structure of the chromosomes
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.
Binding of the chromosomes to the mitotic spindle
Attachment site:
kinetochorkinetochor at the centromer
Preparation of chromosomes, karyotype determination
Blood culture (phytohaemagglutinin) colchicin separation of erythrocytes and white blood cells fixation staining
microphotoarrange according to size, centromer position and banding pattern