L1: cytoskeleton part 2 Flashcards
where are formins?
formins are found in stress fibres (contractile bundle), in cell division within the contractile ring for cytokenesis, phagocytic cuos, cell cortex (gel-like), filopodium (tight paralellel) etc.
F-actin cross-linkers?
fimbrin (monomer) + alpha-actinin (dimer) + spectrin (tetramer) abd filamin (dimer)
- fibrin + actin: tight packing so myosin II cannot enter. parallel bundle.
- alpha-actinin and actin filaments form loose packing so myosin II can enter. contractile bundle.
actin binding proteins?
- actin: forms filaments
- tropomyosin: strengthens filaments
-fimbrin + alpha-actinin: bundle filaments - filamin: cross links filaments into a gel
gelsolin: fragment filaments
myosin II: slides filaments
myosin I: move vesicles on filament
spectrin: attach sides of filaments on pm
thymosin: sequester actin monomers
drugs to intefere?
phalloidin- stabilises f actin
cytochalasin- binds to barbed end, blocks polymerisation
latrunallin- binds to g actin, prevents polymerisation
jasplakinolide- promotoes polymerisation, prevents phalloidin binding
microtubules?
25nm diameter.
made up of alpha and beta tubulin. forms a tubulin heterodimer.most microtubules contain 13 Protofilaments, a linear change of tubulin heterodimers. this organisation makes microtubules ;olar. the - end is closer to the nucleus at the contromere. the plus end is towards the cytoplasm.
regulation of microtubule activity?
Microtubule regulation is controlled by GTP binding and hydrolysis, rather than ATP. GTP binds to β-tubulin within the tubulin dimer, stabilizing a straight protofilament and promoting polymerization. Once incorporated into the microtubule, GTP is hydrolyzed to GDP, causing a conformational change in β-tubulin. This weakens lateral interactions between protofilaments, leading to a curved protofilament structure. When GDP-bound tubulin accumulates, the microtubule becomes unstable, triggering catastrophic depolymerization.
microtubule dynamics/polymierisation?
dynamic instability allows microtubule tips to explore the volume of a cell, searching for and binding to intracellular structures. 1. Individual Subunits (Tubulin Dimers)
Microtubules are made of α-tubulin and β-tubulin dimers.
These dimers exist freely in the cytoplasm before assembling into microtubules.
2. Oligomers (Nucleation Phase)
A few tubulin dimers come together to form small oligomers, serving as a nucleation point.
This is the lag phase, where microtubule formation is slow because the structure is still unstable.
3. Growing Microtubules (Elongation Phase)
Once a stable nucleus forms, dimers rapidly add to the plus (+) end, promoting microtubule growth.
GTP-bound β-tubulin stabilizes the growing microtubule.
4. Microtubules with Subunits Going On and Off (Dynamic Instability)
Once formed, microtubules do not remain static. Instead, they undergo dynamic instability, where tubulin dimers:
Polymerize (grow) when GTP-bound tubulin adds to the plus end.
Depolymerize (shrink) when GTP is hydrolyzed to GDP, causing instability.
This constant switching between growth and shrinkage is essential for microtubule function in cell division, intracellular transport, and cytoskeletal remodeling
how are microtubules arranged?
arranged so that the - is in the cenre and + sticks out depending on cell type.
- look at book has images
microtubule binding proteins?
binding proteins define how tightly packed micrtoubules are,. Ta4: crosslinkers in nerve cell. ;link neighbouring microtubules. tightly packed.
MAP2: links microtubules
ketamine: severs microtubules
plectin: links microtubules to intermediate filaments
MAPs: stabilises microtubules by binding along sides
microtubule functions?
cell division, cillia, sperm cells, nerve cells. Microtubules, with intermediate filaments and microfilaments, are the components of the cell skeleton which determinates the shape of a cell. Microtubules are involved in different functions including the assembly of mitotic spindle, in dividing cells, or axon extension, in neurons.
Gudimchuk and mclntosh (2021):
- during interphrase microtubules rely on their dynamics to facillitate the capture of organelles such as melanosomes and mitochondria initiating their minus end-directed transport. during mitosis, dynamic microtubules search for and capture chromosomes. dynamic instability increases the rate at which chromosomes attach to microtubules.
