AM - Cytoskeleton (2) Flashcards
What do microtubules consist of?
α-Tubulin and β-Tubulin subunits
How are microtubules formed?
- The major Microtubule Organising Centre (MTOC) is the centrosome
- y-Tubulin ring complex of the centrosome synthesises microtubule growth
How do polymerisation and depolymerisation occur in microtubules?
- Polymerisation is driven by GTP hydrolysis
- Depolymerisation occurs through the release of tubulin dimers
How is microtubule assembly regulated?
- Stathmin binds 2 αβ-Tubulin dimers, reducing the free pool (reduces microtubule elongation)
- Polymerisation of free tubulin subunits is energetically favourable
How are microtubules stabilised?
Microtubule Associated Proteins (MAPs) allow crosslinking of microtubules- providing stability
What are intermediate filaments?
They are the most stable component of the cytoskeleton and perform a structural function
How are intermediate filaments formed?
Fibrous polypeptides are believed to assemble side by side to give rise to a filament with high tensile strength
Out of IFs, MTs and MFs which are conserved and which are variable?
Conserved- MFs and MTs
Variable- IFs
What are the 2 major motor proteins involved in the movement along microtubules?
- KINESINS (move toward the plus end)
- DYNEINS (move toward the minus end)
How are microtubules important in axons?
Provide tracks for the movement of vesicles
How is the directionality of movement in microtubules and microfilaments achieved?
Polarity
What are 2 characteristics of motor proteins?
- Globular head region- engages and moves along the filament
- Tail region- attaches cargo to the motor protein
What acts as the motor protein on microfilaments?
MYOSIN
What is the arrangement within Cilia?
9 + 2 arrangement
How does the cilium move?
ATP-driven movement of dynein cause microtubules within cilium to slide against each other - causes cilium to bend
What is the role of the cytoskeleton in cell division?
Important in the separation of chromosomes
- Spindle fibres and contractile ring are structures of the cytoskeleton
What allows for the indirect interaction between actin and the membrane?
Actin Binding Proteins (ABPs)
What are 3 ways of cytoskeletal interactions with the membrane?
- ABPs
- Signal activation of Ezrin-Radixin-Moesin (ERM) interaction with actin
- Binding of the cytoskeleton to the extracellular matrix via integrin
How do mutations in dystrophin result in disorders?
Muscle fibres are no longer strengthened or protected- muscle becomes weaker leading to Duchenne Muscular Dystrophy (DMD)
How do mutations in sarcoglycans result in disorders?
Muscle fibres are no longer connected and sarcolemma is not protected by the joining of the cytoskeleton to the extracellular matrix - muscle lacks connection resulting in Limb-Girdle
Muscular Dystrophy (LGMD)
How do mutations in laminin result in disorders?
Lack of interaction with receptors anchored in the plasma membrane of cells adjacent to the basement membrane- results in Congenital Muscular Dystrophy (CMD)
