i want 25 mutiple choice questions with their model answer below each question that covers different aspects of all of the following information : Appearances
1- The largest structure within the cell.
2- They may be rounded, oval.
3- Often near the cell’s center.
4- One cell might possess two nuclei (Binucleated cell) e.g (liver cells).EM Components of the nucleus
1) Nuclear envelope (or nuclear
membrane).
2) Chromatin
3) Nucleolus
4) Nuclear sap
(matrix, nucleoplasm1) The nuclear envelope
by EM: Two thin membranes separated by a
narrow perinuclear space (30-50nm)---.
- This space &the outer nuclear envelope
connected to the (rER)
-Nuclear lamina ?
1-Highly organized meshwork of proteins
formed of intermediate filaments called
(lamins) attached to inner nuclear
membrane, also it is associated with
chromatin.
2- Stabilize the nuclear envelopNuclear lamina2) Nuclear pore complexs
➢ The 2 nuclear membrane are
bridged by many nuclear pores.
➢ The nuclear pores has a
complex structure (more than
30 core proteins called
(nucleoporins) display 8 fold
symmetry around the lumen
➢ The cell has 3000-4000 pores ----
providing passage up to 1000
macromolecules per secondScanning EM of nuclear poreThe importance of the nuclear envelope and
pores:
1- Maintains the micro-enviroment of the nucleus
different from that in the cytoplasm .
2- Individual pores permit molecular transfer in both
direction simultaneously.
3- Macromolecules shipped out of the nucleus
include ribosomal subunits while the inbound
traffic consists of chromatin proteins & ribosomal
proteins.2- CHROMATIN
What are the chromatin?
Chromatin formed of DNA (double helix
+ PROTEINS (histons)Chromosomes & chromatin
➢ In non dividing cell : it is found in the form of long
threads (double helix strands)= chromatin.
➢ During cell division , become more coiled, more
thicker, found in chromosomes.Two categoeries of chromatin in most
of non dividing cell :
The ration of hetero to euchromatine can provide a
rough indicator of cell’s matabolic activity
1-
Heterochromatin
2-
Euchromatinchromatin
Euchromatin
1- by LM: lightly
basophilic area (not
visiable )
2- By EM : dispersed
granules.
3- increase in active cell
e.g neuron
Heterochromatin
condensed
1- by LM: intensely
basophilic clumps
2-By EM: coarse ,electron
dense.
3- increase in cells with
little synthetic activity
e.g lymphocyteEm : Euchromatin VS HeterochromatinEuchromatin
- Extended.
- Active form :
Very rich in genes
show more
transcriptional
activity
Heterochromatin
- More compact
- Inactive form:
Show little or no
transcriptional
activityLevel of chromatin packing
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Choose who can manage tagsPosition of Heterochromatin inside the
nucleus
(hetero= other.. Chroma=color)
1- Some attached to inner
nuclear membrane
except at nuclear pore.
2- Another parts attached
to nucleolus.What is the function of the
nucleus ?
P. 55 (figure 3-2) 14th edition
P. 58 (figure 3-3) 12th edition3) The Nucleolus
By L.M:
➢ more prominent in Protein forming cell.
➢ They are the large, rounded and basophilic
body within the nucleus.
➢Why it is basophilic?By E.M: nucleolus formed
of
1) Fibrillar region ----(immature form of
ribosomes
1) Granular region (mature ribosomes)
The 2 regions appear different in their
staining and reflect stages of rRNA
maturation1) Fibrillar region; formed of:
a) light staining area:
Nucleolar organizer ----
containing the DNA
sequences that code for
rRNA.
b) Dark area :
Consist of accumulating
rRNA transcripts (newly
formed ).2- Granular region:
- Contains mainly the large &
small ribosomal subunits
being assembled from
rRNA + ribosomal proteins
synthesized & imported
from the cytoplasm …..
- The newly organized small
and large ribosomal
subunits are then exported
back to the cytoplasm
through nuclear poreThe ribosomes
formed of RNA +
PROTEINSFunction of the nucleolus:
The nucleolus is the site where the RNA of
ribosomes (rRNA) is synthesized and produce
ribosomal subunits which assembly into final
form of ribosomes in the cytoplasm