THE NUCLEUS: Description, contents and others

This document is all about the nucleus.

1. NUCLEUS
*plural-nuclei
*from Latin nucleus or nuculeus, meaning kernel
or seed)

2. NUCLEUS
•most prominent organelle of the cell
•The number of nuclei may vary:
a.Uninucleate
b.Binucleate
c.multi-nucleate
*Certain eukaryotic cells such as the mature sieve tubes
of higher plants and mammalian erythrocytes contain
_______ nucleus.

3. *Prokaryotic cells ______ nucleus and is complemented by
_________.
*The contents of the nucleus:
a. DNA genome
b. RNA synthetic apparatus
c. fibrous matrix
*It is surrounded by two membranes, each one a phospholipid
bilayer containing many different types of proteins.

4. •Inmostcells,the________
nuclearmembraneiscontinuous
withtheroughendoplasmic
reticulum,andthespacebetween
theinnerandouternuclear
membranesiscontinuouswiththe
lumenoftheroughendoplasmic
reticulum.Thetwonuclear
membranesappeartofuseat
___________, the ring-like
complexescomposedofspecific
membraneproteinsthroughwhich
materialmovesbetweenthe
nucleusandthecytosol.

5. •Itcontainscell'sgeneticmaterial,
organizedasmultiplelonglinearDNA
moleculesincomplexwithhistones,to
form________________.Thegeneswithin
thesechromosomesarethecell'snuclear
genome.Thefunctionistomaintainthe
integrityofthegenesthatcontrolsthe
activitiesofthecellbyregulatinggene
expression.
A nucleosome is a
section of DNA that is
wrapped around a core
of proteins.

6. NUCLEUS: A Review
•From Latin nucleus or nuculeus, meaning _________________
•Eukaryotes usually have a single nucleus (_____________), but a few cell types, such
as mammalian red blood cells, have no nuclei, and a few others have many
(_________________). Human skeletal muscle cells have more than one nucleus, as
do eukaryotes like fungi. Cell nuclei contain most of the cell's genetic material,
organized as multiple long linear DNA molecules in complex with a large variety of
proteins, such as ______________, to form _______________. The genes within
these chromosomes are the cell's nuclear genome and are structured in such a way
to promote cell function. The _______________ maintains the integrity of genes and
controls the activities of the cell by regulating gene expression—the nucleus is,
therefore, the __________ ___________of the cell.

7. Nucleus Structure
•largestorganelleofthecell
•occupiesabout10%ofthetotalvolumeofthecell
•Inmammaliancellstheaveragediameterofthenucleusis
approximately6micrometers.
•viscousliquidwithinitiscalled___________(karyolymph)
•Thepolynucleatecellsoftheanimalsaretermedassyncytialcells,
whilethepolynucleatecellsoftheplantsareknownas
coenocytes.

9. •Therearealsovariationswithrespecttoshapeand
sizeofnucleus.Itmaybesphericalovaltoflattened
lobeorirregularinshape.Shapeofnucleusalso
dependsonthecell.Thespheroid,cuboidor
polyhedralcells,nucleusisusuallyspheroid.In
cylindrical,prismaticorfusiformcells,nucleusis
ellipsoid.

11. Nuclear Envelope
•nuclear membrane
•two membranes: outer membrane and the inner membrane
•The outer membrane of the nucleus is continuous with the
membrane of the rough endoplasmic reticulum.
•The space between these layers is known as the Perinuclear
space.
•The nuclear envelope encloses the ________ and separates the
genetic material of the cell from the ________ of the cell.
•It also serves as a barrier to prevent passage of macro-
molecules freely between the nucleoplasm and the cytoplasm.

12. Nuclear Pore
•The nuclear envelope is perforated with numerous pores called
___________.
•The nuclear pores are composed of many proteins known as
nucleoproteins.
•The nuclear pores regulate the passage of the molecules between the
nucleus and cytoplasm.
•The pores allow the passage of molecules of only about 9nm wide.
The larger molecules are transferred through active transport.
•Molecules like of DNA and RNA are allowed into the nucleus. But
energy molecules (ATP), water and ions are permitted freely.

13. Chromosomes (Chromatin structure)
•1. The nucleus of the cell contains majority of the cells genetic material in the form
of multiple linear DNA molecules.
•2. These DNA molecules are organized into structures called ________________.
•3. The DNA molecules are in complex with a large variety of proteins (____________)
which form the chromosome.
•4. In the cell they are organized in a DNA-protein complex known as chromatin.
•a. Chromatin = DNA + Histone + DNA binding proteins.
•b. Two type of chromatin are present.
•(i) Euchromatin
•(ii) Heterochromatin

14. •Heterochromatinishighlycondensed,gene-poor,and
transcriptionallysilent.
.Euchromatinislesscondensed,gene-rich,andmore
easilytranscribed(Huisingaetal.2006)

16. •5. During cell-division the chromatin forms well-defined
____________.
•6. The genes within the chromosomes consists of the cells
nuclear genome.
•7. Mitochondria of the cell also contains a small fraction of
genes.
•8. Human cells has nearly 6 feet of DNA, which is divided into
46 individual molecules.

17. Nucleolus
•The nucleolus is not surrounded by a membrane, it is a densely
stained structure found in the nucleus.
•The nucleoli are formed around the nuclear organizer regions.
•It synthesizes and assembles ribosomes and r-RNA.
•The number of nucleoli is different from species to species but
within a species the number is fixed.
•During cell division, the nucleolus disappears.

18. Functions of the Nucleus
•controls the hereditary characteristics of an organism
•1. Storage of hereditary material, the genes in the form of long and
thin DNA (deoxyribonucleic acid) strands, referred to as chromatins.
•2. Storage of proteins and RNA (ribonucleic acid) in the nucleolus.
•3. It is responsible for protein synthesis, cell division, growth and
differentiation.
•4. Nucleus is a site for transcription in which messenger RNA (mRNA)
are produced for the protein synthesis.

19. •5. It controls the heredity characteristics of an organism.
Exchange of hereditary molecules (DNA and RNA) between the
nucleus and rest of the cell.
•6. During the cell division, chromatins are arranged into
chromosomes in the nucleus.
•7. Production of ribosomes (protein factories) in the nucleolus.
•8. Selective transportation of regulatory factors and energy
molecules through nuclear pores.
•9. It also regulates the integrity of genes and gene expression.