CYTOSKELETON Flashcards
WHAT ARE THE FUNCTIONS OF THE CYTOSKELETON?
-internal support of the cell and its structures
-cell signalization and cell division
-movements of the cell and intracellular support
WHAT IS DYNAMIC BALANCE IN RELATION TO THE CYTOSKELETON?
-the process in which the monomer units of the cytoskeletal fibres can detach and reattach
WHAT ARE THE 3 TYPES OF CYTOSKELETAL FILAMENTS?
-microtubules
-microfilaments / actin
-intermediate filaments
WHAT ARE MICROTUBULES?
-monomer of alpha and beta tubulin - dimers polymerize to form protofilaments (13 protofilaments arranged in a circle in one microtubule
-strong, long
-low deformation force, very flexible
-not stable - constantly poly (GTP) /depolymerize (GDP)
-thickest of the fibres - 25nm
-polar - (+) (BETA) end have a bound GTP, which allows for fast polymerization of fibres (–) (ALPHA) end is anchored on MTOC (microtubule organizing centre) slow depolarization occurs
▪ MTOC is typical for eukaryotic cells, is found in the centrosome and is formed by gamma globulin with microtubules emanating from it
WHAT ARE THE FUNCTIONS OF THE MICROTUBULES?
-part of the mitotic spindle, which segregates chromatids into opposite poles of the cell - occurs due to the individual microtubules shortening
(3 types of microtubule fibres
▪ astral – don’t have contact with the
chromosomes, are attached to the membrane
and cytoskeleton, pull MTOC into opposite poles
of the cell
▪ kinetochore – pull chromatids into the direction
of the centrosomes
▪ interpolar – coil with the polar microtubules of
the opposite centrosome and push each other apart)
-flagella and cilia (9 doublets + 1 central pair) allow for movement via dynein protein
▪actively move in only one direction, return via passive movement
-form a path for the movement of organelles (cargo transport)
▪motor proteins such as dynein (moves to - end) and kinesin (moves to + end) move on microtubules
WHAT DRUGS AFFECT THE FUNCTIONS OF MICROTUBULES?
-colchicine / vinblastine / vincristine (stabilization of free tubulin - cannot polymerize, form mitotic spindle and undergo mitosis)
-taxol (stabilization of microtubules - stops the depolymerization of microtubules, cannot undergo mitosis)
WHAT ARE CYTOSTATICS?
-drugs which stop the growth of cells
WHAT ARE INTERMEDIATE FILAMENTS?
-10nm diameter
-not polarized
-never breaks just becomes more deformed
-made up of monomers: lamins, keratins, vimentin, desmin, proteins of neurofilaments
- monomers have a dumbbell shape – central part of monomer is made of an α-helix domain has globular domains on both sides with a C and N end
- monomers coil and form dimers which arrange antiparallel to each other and form a tetramer - tetramer then further coils and forms an intermediate filament
o 1 fibre = tetramer
o 1 intermediate filament = 8 coiled tetramers
(ROPE-LIKE STRUCTURE)
WHAT ARE THE FUNCTIONS OF INTERMEDIATE FILAMENTS?
-mechanical support and formation of cell junctions - do not undergo dynamic remodeling like microfilament or microtubules
-desosomes give strength / mechanical resistance to tissue in the cytoplasm
-lamins give strength to nuclear envelope and anchors chromatin - plays a role in the regulation of intergradation and disintegration of the nuclear envelope
WHAT ARE MICROFILAMENTS?
-7nm diameter
- monomer is G-actin (Globular), which polymerizes and forms a double helix F-actin (fibrous)
-organized into linear bundles, 2D networks and 3D gels
-polarized + (ATP = polymerization) and - (ADP = depolymerization) end, actin filaments face in the same direction
- dynamic stability 🡪 grows and then shortens (polymerizes and depolymerizes) -“Treadmilling”
-highly concentrated in the cortex beneath the plasma membrane
-break easily
WHAT ARE THE FUNCTIONS OF MICROFILAMENTS?
- Microvilli – fine hairs on the cell surface, niches of the plasmatic membrane which increases cell surface without increasing cell size
- Cell cortex– under the plasmatic membrane, give mechanical support
- Lamellipodia (flat projections) and filopodia (finger-like projections) aid in amoeboid locomotion of the cell
- Contractile ring – used in cytokinesis to separate cells
-Contractile bundles – with the help of myosin work as the muscle of cell -> movement
WHICH DRUGS AFFECT THE FUNCTION OF MICROFILAMENTS?
- latrunculin – binds to free actin and prevents polymerization
- phalloidin – stabilizes microfilaments, blocks polymerization
WHAT PROTEINS BIND ACTIN?
-spectrin (shape of erythrocytes)
-dystrophin (binding of microtubules to basal lamina)
WHICH KIND OF TUBULIN IS FOUND IN THE CENTROSOME AND IN THE CENTRIOLES?
-gamma tubulin
WHAT DOES THE FOCAL CONTACT CONNECT TO?
actin filaments
