Nucleus & Mitosis Flashcards
General roles of the nucleus
-contains genetic information
-contains the nucleolus which is the site of rRNA production
-bound by a double membrane containing nuclear pores; this controls movements of material from cytoplasm into nucleus and vice versa
neoplasm definition
nuclear content other than nucleus and chromatin
85% = proteins and nuclear bodies
15% = nucleic acids
1% = lipids
structure of nuclear lamina
-adjacent to the inner nuclear membrane
-lamin A and C form a mesh of intermediate filaments
-lamin B allows the linking of the mesh to the inner nuc membrane (due to LBR - lamin B receptor)
!! lamins disassemble during mitosis and reassemble after cell division is done
main characteristics of nucleus that differ in different cells (5)
- different size
-different location
-absent in some cells
-more than one nucleus can be found in some cells
-nuclear cytoplasmic ratio differs
Chromatin def structure
-substance within chromosomes containing DNA + proteins
1. heterochromatin: condensed and doesn’t allow transcription
- euchromatin: looser and allows transcription (less steric hinderence)
-density of the chromatin reflects biosynthetic activity in the cell
Function andsize of nuclear pores
-made by the fusion of the inner and outer nuc membrane
-abundant in HIGHLY ACTIVE cells because they control the transport of molecules into and out of nucleus using transport proteins and receptors
-roughly 125 nm in diameter
NPC structure
-made of 2 rings: one cytoplasmic and one nuclear each containing 8 subunits
-they are attached to plasma membranes via anchoring proteins
NUCLEAR PORTION: connection to nuclear basket and distal ring
CYTOSOLIC PORTION: ring connected to cytoplasmic filaments
-CENTRAL PORE COMPLEX: makes the hole of the pore in the center of the membrane proteins
Receptors for regulation found in the NPC
IMPORT: nuclear localisation signal (NLS) using the importin receptor
EXPORT: nuclear export sequence (NES) using the exportin receptor
UPON RECOGNITION: complexes are driven through the pore using RanGTPase which hydrolyses GTP on fibrils
function of nuclear lamina
-makes up the nucleoskeleton
-provides shape and stability
-provides structural link between DNA and nuc envelope
-become phosphorylated/ dephosphorylated during mitosis for the destruction/ reassembly of the nuc membrane
specific proteins in the nucleoskeleton that should be memorised
- spectrin - connect to cytoskeleton
- nesprin and titin: connect to chromatin
- laminins and actin: free in nucleoplasm
cycle of nuclear lamina during mitotic division
INTERPHASE: unphosphorylated lamins means the nuclear membrane is present
PRO-METAPHASE: phosphorylation of lamins causes the disassembly of nuclear membrane
TELOPHASE: dephosphorylation of lamins and fusion of vesicles of the nuclear envelope to reassemble the membrane
common pathologies caused by the malfunction of nuclear lamins
-mutations affect the organisation of chromatin domains so there is different gene transcription causing different cell phenotypes
3 main laminopathies:
1. muscular laminopathies
2. lipodystrophies
3. developmental progeroid syndrome
structure of the nucleolus
-not membrane bound
-basophilic (intense stain)
3 REGIONS:
- Fibrillar center: DNA loops of chromosomes containing rRNA genes. light staining area
- Dense fibrillar material: rRNA processing precursors. dark staining areas
- Granular material: ribosome assembling region. appear as granular in staining
!! 2 and 3 make up the nucleonema.
What staining can be used to visualize nucleus morphologies in mitosis?
FEULGEN STAINING:
-stains DNA in dark red
-intensity of dye depends on degree of chromatin condensation (darker for hetero and lighter for eu)
3 different types of microtubules found in anaphase + function
- kinetochore MT: connects spindle pole with kinetochore of dividing chromosomes
- interpolar MT: connect 2 spindle poles
- astral MTs: in charge of mediating association of spindle pole with membrane of the 2 cell poles
change in length of microtubules during anaphase
interpolar: lengthen
kinetochore and astral shorten
classifications of dividing tissues (3)
- TRANSIENT: continuous replication (eg. lining epithelia). separated into slow and fast activity depending on speed of division)
- STABLE: do not continuously replicate but are able to divide in response to stimuli (eg. glands and liver tissue)
- STATIC: unable to divide (eg. highly specialised cells - neurons, cardiac and skeletal muscle)
Compare and contrast necrosis and apoptosis
-N has an extracellular cause (injury), AP has intracellular cause (cascades)
-N is unplanned and passive, AP is planned and active
-N has degeneration of organelles, swelling of ER and disruption to plasma membrane, AP has no membrane degeneration but is characterised by condensing of chromatin and apoptotic body formation
-N causes inflammatory response and AP doesnt
-
