Lecture 10: The cytoskeleton 2 Flashcards
What is the overall process of cell migration?
- Polymerisation of actin monomers at leading end pushes plasma membrane forwards
- Forms new region of actin cortex
- New anchorage points made between bottom of cell and surface
- Contraction of rear end mediated by myosin II motor proteins draws body of cell fowards
- New anchorage points made at front and old ones at the back released
- Cycle repeats
What are the three main mechanisms of animal cell migration?
Cell pushes out protrusions at leading edge of cell
Protrusions adhere to surface
Rear of cell is pulled forwards
What is the role of the Arp2/3 complex as the cell pushes out protrusions?
- Complex binds to side of existing actin filaments
- Nucleates assemble of new actin filaments and causes branching
- Prevents disassembly at minus end
Where is the main nucleator of actin filaments located?
Lamellipodia
What is the role of actin polymerisation as the cell pushes out protrusions?
- Actin polymerisation pushes cell forwards
- Actin filaments disassemble at the rear of the lamellipodium
What are filopodia?
Extend by actin polymerisation pushing on plasma membrane
Role in guiding migrating cell by probing environment and establishing new contacts
What are formins?
Actin nucleating proteins attached to plasma membrane
Add actin monomers to plus end of actin filaments to form filopodia
Why don’t formins slide back?
Anchored into place by interactions with other actin filaments via cross linking proteins
How do protrusions adhere to the surface?
Focal contacts contain integrins
Contractile actin bundles attach to focal contacts
How is the rear of the cell pulled forwards?
Motor protein myosin II
What are the two different types of intermediate filaments?
Cytoplasmic : found in animals except arthropods or hydra
Nuclear : found in all animals
What is an example of a cytoplasmic intermediate filament?
Keratin filaments
What is an example of a nuclear intermediate filament?
Nuclear lamins
What are nuclear lamins?
Made up of intermediate fibres underlying the nuclear envelope in nucleated cells
How can nuclear lamins cause disease?
Mutations can lead to diseases like progeria
What are some properties of intermediate filaments?
10nm diameter
Don’t bind to nucleotides Strong and durable
Stable
Disassemble in cell division and reassemble in telophase
What is the role of intermediate filaments?
Strengthen cells
Protect against stretching
What occurs when there is a mutation in keratin filaments?
Skin is more prone to blistering
Cells rupture between the nucleus and hemidesmosomes connecting cells to basal lamina
What are some effects of desmin mutations?
Muscular dystrophy
Cardiac myopathy
How is desmin linked?
Desmosomes
What is the role of desmin?
Maintain organisation in the cell
What are neurofilaments?
Strengthen neurons
Aberrant accumulation in cell bodies and axons can cause ALS
How are intermediate filaments assembled?
Symmetrical
Non-polar
Why are intermediate filaments symmetrical and non-polar?
Dimers align into pairs in an antiparallel fashion
Overall filament is symmetrical
Held together by covalent bonds
What are some effects of plectin mutation?
Helps interaction between filament systems
Can cause skin disruption muscular dystrophy and neurodegeneration
What is the filament in intermediate filaments?
8 stranded flexible helix
10nm diameter
What are the stabilising and destabilising drugs of intermediate filaments?
None
