L22 Cell Motility: Microtubules And Actin Filaments Flashcards
What do cell motility need?
Energy and guidance (direction) and mechanical interaction with something outside the cell
What are the two structures that are needed for microtubule- based motility?
Cilia and flagella
What are cargoes?
cargoes refer to the specific molecules or substances that are being transported into the cell through this process
What are the cargoes of cells?
Protozoa
Sperm
What are the cargoes of fluids?
Respiratory
Reproductive tract
Give adaptation of microtubules
Hollow tubule (of alpha and beta tubulin) - rigid structure
Cross section is 24nm in diameter (13 protofilaments)
Alternating alpha and beta tubulin creates a tubulin dimer
What are the similarities and differences between cilia and flagella structure?
Similarity:
Same structure
Differences:
Different length
Cilia: 2-10. X 0.25um
Flagella: 100-200 x 0.25um
What is the axoneme?
It’s the core structure of cilia and flagella, responsible for their movement
What are the key features of an axoneme?
Complete (A) fibres 13 protofilaments
Incomplete (B) fibres 10 protofilaments
- Dynein arms: motor proteins generates sliding motion between microtubule pairs
- Typically a “9+2” structure with 9 pairs of microtubules arranged in a ring around a central pair
Nexin links: Connects adjacent microtubule doublets, limiting slide and coordinating movement (causes a bend)
How are the waveforms different for cilia and flagella? (Write which uses inner and outer arm)
Cilia - back and forth pattern, resembling a whip-like motion
Flagella - wave like motion
What does Nexin do?
Forms a bridge joining the pairs of A and B microtubules.
Describe the structure of basal body
Instead of 9+2 its 9 x 3 microtubule array
0.2 um x 0.4 um (diameter x length)
Cylindrical pattern
What is basal body?
It’s a modified centriole, serving as the anchor of the axoneme
Where can the motility for the actin- based motility come from?
Motors and turnovers
Describe the structure of actin filament structure
Actin filament has polarity - plus and minus end
ATP hydrolysed when filament polymerises
Describe the structure of microtubule structure (listen to the guy)
- Alpha and beta subunit dimers.
- Nucelotides in both are GTP/GDP.
What are tubulin dimers?
Each tubulin dimer consists of an alpha and beta tubulin protein
What are protofilaments?
Tubulin dimers polymerise head to tail to form linear chains called protofilaments
What is actin treadmilling?
Where monomers are continuously added to one end and removed from the other end of an actin filament
Compare the actin filament vs microtubule structure
- Diameter - 5-9, 24
- Form - Solid, hollow
- Subunits - Homomeric, a/b heterodimers
- Nucleotide in monomer - ATP, GTP.
Describe the myosin structure
Head domain: motor domain of myosin
Contains binding sites for actin and ATP
What structures do actin need?
- Filopodium - thin, finger - like protrusions that extend from the cell surface
- Lamellipodium - sheet-like protrusions that form at the leading edge of migrating cells
- Stress fibres -
Cortical actin
What does profilin does to monomers?
- Inhibits nucleation
- binds to ATP actin
What does cofilin do?
Severing action.
Processes of Actin-Binding Preoteins?
- Monomer nucleating
- Monomer sequestering
- Capping
- Monomer polymerization
- Depolymerizing
- Bundling
- Filament severing
- Membrane Binding
What is myosin?
It is the microfilament motor protein for Cytoskeleton or muscle which has actin filament.
Describe the structure of Myosin?
- C-terminus and N-terminus at ends.
- Coiled with two alpha helices
- Two light chains at the Nterminus end
- 150nm long and 2nm wide
