Lecture 22: Motors, Actin, Cell Motility Flashcards
Microtubules (MT) types
Axonemal MT - highly organized, stable, part of structures involved in cell movement
Cytoplasmic MT - loosely organized, very dynamic, located in cytosol
About microtubules (MT)
- largest cytoskeletal element
- polymer of two different proteins (monomers): alpha tubulin and beta tubulin
What is a heterodimer?
Alpha and beta particles together which forms long protofilaments
How many protofilaments make a microtubule?
13 protofilaments in longitudinal array
A microtubule is _______
Hollow
Orientation of microtubules?
- polarity present
- fast-growing plus end - more dynamic, not a positive charge just the name
- slow-growing minus end
Microtubule organizing center (MTOC)
Central site of MT assembly, only in eukaryotic cells, microtubule grows away from MTOC, therefore the plus end is always the farther part of the MT from the MTOC, and the negative end is closest to MTOC
What binds the MT’s?
Microtubule associated proteins: which modulate assembly and function and mediate interactions with other structures
- Non-motor proteins
- Motor proteins
MT-associate non-motor proteins functions
- control MT organization in cytosol (Tau, and MAP2)
- stabilizes MT band stimulates assembly
Defective Tau protein consequences?
- neurofibrillary tangles -> Alzheimer’s disease
MT-associated motor proteins functions
- use ATP to generate force
- can move material along MT track
- can generate sliding force between MTs
- kinesin: plus end directed
- dynein: minus end directed
Kinesin receptor attaches Motor protein to vesicle
Zebra fish Kinesin and dynein
Kinesin: darkly coloured
Dynein: lightly coloured
Microfilaments functions
- maintenance of cell shape
- cell movement
- vesicle transport
- muscle contraction
- cytokinesis
Microfilaments
- 8nm
- polymer of actin protein
- plus and minus end
Microfilaments (MF) monomers and polymers
- Monomer - G-actin: four subdomains
- Polymer - F-actin: 28 subunits of G-actin make up this unit, two strands of G-actin monomers
MTs plus and minus end
Plus end is fast growing
Minus end is slow
They are polar
Phalloidin and actin?
Once binded to actin, you can track actin using fluorescent phalloidin, come from mushrooms
proteins in microfilaments?
Actin-binding proteins help to organize microfilaments
Which two ways can microfilaments be assembled?
microfilaments can be arranged in loose network OR in tight bundles
F-actin microfilaments are associated with _________
Motor proteins
What are myosin’s in microfilaments?
Motor proteins associated with microfilaments, there are two types:
1. Conventional myosin’s: Type II, primary motors for muscle contraction
2. Unconventional myosins: type I and III-XVII, organelle and vesicle movement
Myosins move towards ______ end of microfilaments
Plus
MT and MF based motors cooperate in ______
Intracellular transport (e.g. movement of pigment to PM)
Intermediate filaments (IF) functions
- 10 nm diameter
- exclusive to multicellular animal cells
- provide structural support and mechanical strength
- stable in comparison to MT and MF
- arrangement of fibrous alpha helical proteins
- NOT POLAR
Types of intermediate filaments
Keratins - in cytosol
Lamins - in nucleus
In axons of neurons, IF’s….
Arranged in stacks
