HS120: The Nucleus Flashcards
Properties of the Nucleus:
- it is the largest membrane-bound structure of the cell
- the command centre of the cell
What are the functions of the nucleus?
- houses genetic material
- contains the molecular machinery to replicate DNA
- contains the molecular machinery to synthesize & process all types of RNA
- stores genetic information on its genes & transmits them to succesive generation
What does the genetic material in the nucleus do?
directs all cellular activities & regulates cellular structure
Classification of cell based on number of nuclei:
- Mononucleated: one nuclei
- Binucleated: 2 nuclei
- Multinucleated: more than 2 nuclei
How many nuclei are found in most body cells?
1 (mononucleated)
Which cells are binucleated?
- liver cells
- dome cells of transitional epithelium
Which cells are multinucleated?
- osteoclasts
- skeletal muscle fibre
Which body cells do not have a nucleus?
- mature erythrocytes/ RBCs
- blood platelets
Classification of nucleus based on position:
- central
- eccentric
- peripheral
Classification of nucleus based on shape:
- spindle/ elongated
- kidney shaped
- segmented
- lobulated
- rounded
What does the nuclear shape often reflect?
with examples
It often reflects the shape of the cell.
ex. simple cuboidal epithelia (rounded)
vs
simple columnar epithelia (elongated)
What is the microscopic appearance of nuclei under L/M?
2 ways it appears
-
vesicular/ open faced
- lightly stained nucleus (still basophilic because of nucleic acids)
- its details can be identified (i.e apparent nucleolus)
- used for metabolically active cells (liver & nerve cells) -
condensed
- deeply stained nucleus
- its details cannot be identified
- metabolically inactive cells (ex. small lymphocytes)
`
Where can the nuclei be seen as uniform in size and shape?
In simple columnar epithelia.
What are the components of a nucleus, assuming it is in an interphase cell? And what microspocy is used for it to be seen?
In EM, the components of the nucleus are:
1. nuclear envelope
2. chromatin
3. nucleolus
4. nucleoplasm/ karyoplasm / nuclear sap
Properties of nuclear envelope
- EM
- perinuclear cisterna
- nuclear pores
nuclear envelope disappears during cell division.
Define nuclear pores
where the nuclear membranes fuse with each other at certain regions to from perforations.
Define perinuclear cisterna
the 30-50nm space that separates the 2 concentric membranes of the nucleus.
What is the outer nuclear membrane?
- the membrane that faces the cytoplasm
- continuous with RER
- usually possesses ribosomes
What do the ribosomes on the outer membrane of nucleus do?
They actively synthesize transmembrane proteins that are destines for the outer or inner nuclear membranes.
What is the inner nuclear membrane?
- membrane that faces the nuclear contents
- close contact with nuclear lamina
What is nuclear lamina?
- interwoven meshwork of intermediate filaments located at the periphery of the nucleoplasm
- 4 types: lamins A/B1/B2/C
What microscope is used for nuclear lamina?
Electron, just like the rest of the nuclear envelope
what is the function of lamins?
- help in organizing & providing support to the lipid bilayer membrane
- “nucleoskeletal” function
- distribution & function of perinuclear chromatin
- formation of NPCs & assembly of vesicles during the reformation of the nuclear envelope after cell division
what is the function of the nuclear envelope?
- segregates the cytoplasm & nucleoplasm
- selectively-permeable membrane
- assists in organizing chromatin
what are nuclear pores?
- interruptions in the nuclear envelope
- inner & outer nuclear membranes fuse with each other
- they are 100nm in diametre
what is the function of nuclear pores?
permit communication between the nuclear compartment & the cytoplasm
What is the number of nuclear pores related to?
Directly proportional to the amount of metabolic activity of a cell.
How many nuclear pores are often found in growing cells?
- 3000 to 4000 of them, with 1000 macromolecules being transported within one of them per second (transportation is in both directions simultaneously)
What is EDMD?
Emery-Dreifuss muscular dystrophy:
- autosomal dominant
- muscular dystrophy caused by a mutation in lamins A & C
- tissue specific, affecting:
1. striated muscle
2. skeletal development
3. adipose tissue
4. peripheral nerves
What are the symptoms of EDMD?
- early onset contractures of major tendons
- slow muscle weakness
- muscle wasting in upper & lower limbs
- cardiomyopathy (heart muscle weakening)
What are the components of NPC?
- cytoplasmic filament/fibres
- cytoplasmic ring
- luminal spoke ring
- nuclear/ nucleoplasmic ring
- nucleic basket & distal ring
- central plug
Cytoplasmic fibres…
import substrates to the nucleus via the NPC
cytoplasmic ring…
the ring that faces the cytoplasmic aspect of the NPC.
- made of 8 (symmetrical) subunits, each attached to GTP-binding proteins and a cytoplasmic filament.
What is the nucleoporin?
It is the 3 ring-like arrays that are interconnected by a series of spokes.
The luminal spokes ring…
- anchor glycoprotein of the NPC to the rims of the nuclear pore
- made of 8 transmembrane proteins that project into the lumen of the nuclear pore & into the perinuclear cisterna.
The nuclear ring…
is the ring of the nuclear pore that faces the nucleoplasmic aspect of the nuclear pore.
- assists in exporting all types of RNA
Nuclear basket…
- filamentous & flexible
- suspended from the nucleoplasmic ring & protudes into the nucleoplasm
Central plug/ transporter is…
the material that is being transported to/ from the nucleus
Functions of the NPC:
- meditates the bidirectional nucleocytoplasmic transport
macromoleculs that are…
- shipped out: ribosomal subunits & RNA associated with proteins
- shipped in: chromatin proteins, ribosomal proteins, transcription factos, & enzymes
How does NPC transport method change?
depending on the size of macromolecule.
Transport of large molecules:
active transport through pore via GTP
Transport of small molecules:
ions and small water-soluble molecules cross NPC via simple diffusion.
Nucleolus in L/M:
- spherical & highly basophilic subdomain of nucleus.
- intense basophilia due to densely-concentrated rRNA
- H/E stain is used
Nucleolus under E/M:
- appears spongy due to the lightly-stained fibrillar centres.
What are the components of nucleoli under L/M?
and what happens in them
- fibrillar centres (NORs): genes 13, 14, 15, 21, 22 on DNA loops that code for rRNA, RNA polymerase 1, & transcription factors. The nucleolar-organizer region is where the gene loci that encodes for rRNA is located.
- pars fibrosa: genes that are actively undergoing transcription & large amounts of rRNA.
- pars ganulosa: densely-pack preribosomal particles & site of initial ribosomal assembly
- nuclear matrix: a network of fibres active in nucleolar organization
Nucleolus qualities:
- its size, number, & shape relate to the synthetic activity of the cell
- some cells contain more than one nucleolus per cell
- disappear during cell division
Function of nucleolus:
- rRNA synthesis and in the assembly of small and large ribosomal subunits
- synthesis of some regulatory RNAs
- regulating events in the cell cycle like cytokinesis
What happens to rRNA in the nucleolus?
it is associated with the ribosomal proteins that are imported from the cytoplasm via nuclear pores. Then after these ribosomal subunits are organized, they are exported back to the cytoplasm through those same nuclear pores.
What is the nucleoplasm?
- a viscous substance that surrounds the chromosomes & nucleoli
- composed of interchromatin & perichromatin granules, water, ribonucleoproteins (RNPs), & nuclear matrix.
