Cytoskeleton and Cell Division Flashcards
cytoskeleton provides structural support for
plasma membrane and cell organelles
functions of cytoskeleton (3)
- intracellular movement/transport of substances (large molecules/organelles)
- cell locomotion (amoeboid movement, embryonic development, cili, flagella)
- muscle contraction (specialized cells)
3 main elements of cytoskeleton
microfilaments
intermediate filaments
microtubules
microfilaments are important in maintaining
cells shape
facilitate shape during movement
actin diameter
6-8 nm
actin strands are made of
smaller G-actin subunits
G actin
small, globular protein monomer, polymerizes to form protofilaments
2 protofilaments twist together to form a
double helix, F actin
actin links with filamin beneath the plasma membrane to form a
support meshwork called cell cortex (terminal web)
actin prevents the cell from
deformation by reenforcing the phospholipid bilayer
actin is also found in (2)
microvilli
stereocilia
myosin thick filament diameter
15 nm
myosin is classified as
motor protein along with dyenin and kinesin
myosin shape
long and rod shaped with globular heads
myosin forms
thick, ropy cables with myosin heads sticking out the sides (braiding golf clubs)
myosin heads form
cross-bridges between adjacent filaments
what is required for muscle contraction? (2)
Ca
ATP
intermediate filaments diameter
8-10 or 10-15 nm
intermediate filament structural function
1’
heterogenous group
molecular makeup varies between cells
generally forms large filaments which bind with
intracellular structures
there are several different classes of intermediate filaments, meaning
1 cell may produce more than 1 type of filament
intermediate filaments are useful in (2)
immunohistochemistry
tumor ID
cytoketatin
characteristic of all epithelial cells
cytokeratin in the epidermis of the skin forms
tonofibrils
vimentin
found in mesodermal cells of mesenchymal origin
(includes endothelial cells, muscle cells, neuroectodermal cells
desmin
unique to muscle cells, mesodermal origin
neurofilament proteins
present in nerve cells (neurons)
GFAP
found in glial support cells of the nervous system
astrocytes
lamin
forms a layer on the inside of the nuclear membrane
intermediate filaments (6)
cytokeratin vimentin desmin neurofilament proteins GFAP lamin
microtubule diameter
24 nm
microtubules are compoased of which 2 globular protein subunits
alpha and beta tubulin
arranged in a coiled, spiral pattern
microtubules polymerize to form
hollow tubes
readily assembles and disassembles
microtubules are involved in (3)
cell movement
maintenance of cell shape
intracellular transport of substances
microtubule movement occurs via
addition or subtraction of tubulin subunits from microtubules
motor proteins — & — attach microtubules to organelles to allow for movement in the cytoplasm
dyenin
kinesin
various microtubule-associated proteins (MAPs) provide
energy as ATPase
stabilize microtubules along with
capping proteins
classic example of microtubules during cell division
cell spindle
drugs that inhibit polymerization of microtubules and cell division (3)
colchicine
vincristine
vinblastin
microtubules are found in (4)
cilia and flagella
centrioles
basal bodies of cilia
mitotic spindles
axoneme
9 pairs of microtubules (peripheral doublets) containing dynein arms (link doubles together) arranged in a circle with a central doublet in the middle
(9+2 structure)
central doublets connect to peripheral doubles by
radial spokes
peripheral doublets connect to each other by the protein
nexin
in cilia, the basal axoneme grows from the
basal body
derived from modified centriole
centrioles are normally located in the
centrosome
cell center, near nucleus and function in cell division
centrioles during cell division
pair of centrioles (diplosome) oriented at right angles to each other within the centrosome
each centiole consists of
9 triplets of microtubules arranged in a cylinder
centrioles acts as a — — for microtubules
nucleation center
during mitosis, centrioles divide and each pair goes to the opposite poles of the cell to form the
mitotic spindle
the mitotic spindle controls the
distribution of chromosomes in daughter cells
movement of chromosomes occurs via addition and subtraction of tubulin subunits and attachment proteins (dyenin and kynsesin) to — at the
chromatids
kinetochore (centromere)
what happens during mitosis?
growth and replication of the cell
mitosis phases
interphase prophase metaphase anaphase telophase
what is interphase?
the resting phase, or time between divisions
which phase occupies most of the life of a cell?
interphase
subphases of interphase (3)
G1
S
G2
G1 phase
first gap phase
which phase is the longest?
G1
what occurs during G1 phase? (3)
cell growth
maturation
differentiation
hypertrophy
increase in cell size
hypertrophy occurs during
G1
hyperplasia
increase in cell number
hypertrophy occurs during
mitosis
S phase
synthesis phase
what occurs during S phase?
replication of DNA prior to division
at the beginning of S phase, chromosome number is –, at the end it is –
2n
4n
prior to replication, in S phase, each chromosome has a — — with an — —
single chromatid
attached centromere
following replication in S phase, each chromosome contains - chromatids connected by a —
2
centromere
when does replication of centrioles occur?
S phase
2 diplosomes
G2 phase
2nd gap phase
what occurs during G2 phase?
preparation for mitosis
during G2, — and — are synthesized for the mitotic spindle
ATP
tubulin
M phase
cell division portion of mitosis
M phase is characterized by — followed by —
karyokinesis (nuclear division)
cytokinesis (cytoplasmic division)
M phase results in
2 daughter cells
how long does S, G2, and M phase take?
several hours each
during S and M phases, chromosomes
condense
become visible, look like coiled snakes
during G1 and Go, chromosomes exist in an
unraveled mass
some cells lose the capacity for
cell division
is Go permanent or reversible?
it can be either depending on the cell type
facultative dividers
retain capacity for division with the proper stimulus
ex. reserve stem cells
terminally differentiated cells
lose capacity to divide
ex. neurons, cardiac myocytes
during prophase, chromosomes are visibly
condensed
during prophase, microfilaments an microtubules of cytoskeleton
disaggregate
during prophase, centrioles migrate to poles of the cell, form spindle apparatus with — — between them
interpolar microtubules
— — and — disappear at the end of prophase
nuclear membrane
nucleoli
during prometaphase, mitotic spindle attaches to
chromosomes at the kinetochore
during metaphase, chromosomes
line up along the equator (metaphase plate)
during anaphase,
centromeres split apart, chromosomes migrate to opposite ends of the cell
chromosomes are pulled by microtubules connecting
centriole and kinetochore
during telophase, the mitotic spindle
disaggregates
what reappears during telophase? (2)
nuclear envelope reassembles
nuclei reappear
during telophase, the plasma membrane forms a — —
cleavage furrow
cytokinesis results in
2 genetically identical. daughter cells
plant cells dont make a cleavage furrow, they make a
cell wall in the middle of the cell
mitotic index is used to describe the
proportion of cells in a tissue in mitosis at any given time
mitotic index is important in
tumors
estimated by counting the number of mitotic figures/HPF (normally <1)
sexual reproduction requires the production of
haploid gametes (egg and sperm)
haploid gametes are produced via
gametogenesis
spermatogenesis
occurs only in germ cells of male gonads
oogenesis
occurs only in germ cells of female gonads
meiosis involves chromosomal duplication followed by – consecutive cell divisions in haploid gametes
2
fusion of gametes (fertilization) produces
diploid zygote (fertilized egg)
meiosis result sin the formation of
two daughter cells
meiosis 1 differs from mitosis in what two ways?
during prophase 1, homologous pairs of chromosomes form tetrads, with exchange of chromatin via crossing over (chiasmata formation)
results in hybrid chromatids different from parents
each chromosome pair has potential for crossing over during prophase 1 (23 pairs total in humans)
centromeres do not split during anaphase 1
why do we want crossing over?
if the environment changes and you want your offspring to survive, you want variation within your offspring so some of them may survive
between the first and second meiosis, there is a brief
interphase 2 (interkinesis) with no replication of DNA
there is no — — in prophase 2
crossing over
during anaphase 2,
centromeres split
during telophase 2,
cytokinesis yields four haploid gametes, each genetically unique
during gametogenesis in males, - or - visible gametes (sperm) are produced
3 or 4
during gametogenesis in females, cytoplasmic division is
unequal
1 functional gamete (ovum) and 2 or 3 functional polar bodies
when does spermatogenesis begin?
when does oogenesis begin?
puberty
during fetal development
oogenesis timeline
begins during fetal development
female germ cells enter prophase 1 about 5th month of gestation during fetal development and stop
remain in prophase 1 until ovulation (12-50 years later)
some cells have a finite, predetermined life span, such as (2)
epithelial cells of skin
GI tract
apoptosis occurs during — development
fetal
webbed tissue
apoptosis can occur during the growth and regulation of
ovarian follicles and CL
apoptosis can be triggered by the destruction of
virus/tumor infected cells
clonal deletion in thymus
apoptosis to remove t-cells that react to self molecules
failure of clonal deletion may lead to
autoimmune diseases (the body produces antibodies to itself)
apoptosis mechanism
condensation of nuclear chromatin and shrinkage of the nucleus (pyknosis)
cell swells as a result of influx of water due to loss of ATP to maintain pumps in the cell membrane
lysosomes release catalytic enzymes into the cytoplasm (autolysis)
the cytoplasm becomes bright pink (eosinophilic)
pyknosis
shrinkage of the nucleus
autolysis
when lysosomes release catalytic enzymes into the cytoplasm
the final apoptosis pathway is initiated by
caspace cascade
caspases are normally
inactive enzymes
karyolysis
chromatin in nucleus begin to degenerate
karyorhexis
nuclear material begins to fragment and nuclear membrane disintegrates
apoptotic bodies
fragmented nuclear debris
apoptosis results in dead, — cells
necrotic
necrotic cells are later phagocytosed by
neutrophils
necrosis also refers to death of cells as a result of (3)
inflammation, traumatic injury, or pathology
