II' INTERNAL ORGANIZATION OF EUKARYOTIC CELLS

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II. INTERNAL ORGANIZATION OF EUKARYOTIC CELLS
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Structure of a typical animal cell
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Structure of a typical plant cell
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II.1.4. Nucleus
Biological significance storage, expression and
transmission of the genetic information.
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Segmented nuclei of leukocytes
neutrophils
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Structural components
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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.
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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.
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Nuclear pore
EM image
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Relationship of the nucleus and the cytosol
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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).
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.
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Euchromatic nucleus of neuron
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Structure
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.
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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).
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3. Level of organisation 300 nm chromatin fibers
300 nm
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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 detecteble
units. At the start of the mitosis (M phase)
each chromose has replicated and consists of two
sister chromatids joined together
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Fine structure
Chromatids 300 nm chromatin fiber form spirals
(packing level 10 000 x)
700 nm
300 nm
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Staining of the chromosomes
Fluorescent stains (e.g. Quinacrin)
Q-bands
specific for
AT-rich DNA regions Giemsa-stainingaccording
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
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Chromosomes
The human karyotype
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Chromosomal organization of different species
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
bakers yeast 32 corn 20
rice 24 wheat 42 tobacco 48
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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
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Structure of the chromosomes
X
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Scanning-EM, human chromosomes
Schematic view of chromosomal regions
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5
1
4
1
3
1
2
1
1
1
1
2
2
2
3
3
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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.
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Binding of the chromosomes to the mitotic spindle
Attachment site kinetochor at the centromer
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Preparation of chromosomes, karyotype
determination
Blood culture (phytohaemagglutini
n) colchicin separation of
erythrocytes and white blood cells
fixation staining
microphoto
arrange according to size, centromer position and
banding pattern