Eukaryotic Structure 6 Flashcards
(23 cards)
What is another name for actin filaments ?
Micro filaments
Where can you find actin filaments ?
- Microvilli
- Contractile bundles in cytoplasm
- Filopodia of migrating cells
- Contractile ring during cell division
Describe the structure of actin filaments
Made up of actin monomers which are globular proteins.
The actin monomers have a binding site for either ATP or ADP.
Two-stranded helical protofilament with a twist repeating every 37nm.
There is a plus end and minus end.
Describe the plus and minus end of actin filaments
Plus end (barbed end)- grows quickly
Minus end (pointed end)- doesn’t really grow
What is polymerisation of the actin filament ?
- Actin monomers in cytosol carry ATP
- ATP is hydrolysed to ADP as actin monomers assemble into the growing actin filament
- ADP remains trapped within the filament until the actin monomers dissociates from the filament
What is “treadmilling” of actin filament ?
The filament reaches a dynamic equilibrium= monomers are added to the plus end at the same rate that they are lost from the minus end.
The actin filament length remains unchanged.
Describe cell migration- protrusion (1)
The cell extends part of its membrane to form lamellipodia due to actin polymerisation
Describe cell migration- adhesion (2)
Attachment to extracellular matrix via focal contact
Describe cell migration- translocation (3)
Myosin motor proteins draw the cell body forward
Describe cell migration- de-adhesion (4)
Release of old focal point.
Cells crawl forward
What are bundling proteins ?
Actin filaments that are organised into tightly packed parallel or anti-parallel bundles.
They stabilise actin filaments in structures like filopodia and Microvilli.
Fascin is the protein in filopodia.
What are the thick and thin filaments in muscle fibres ?
Thin= actin
Thick= myosin-II
How do bacteria “hijack” actin cytoskeleton ?
They use actin cytoskeleton as a host to move in an invade neighbouring cells
What are the toughest and most durable cytoskeleton filaments?
Intermediate filaments
They are rope like
What are the main components of the cytoskeleton?
- Intermediate filaments
- Actin filaments
- Microtubules
Describe the structure of intermediate filaments
Alpha helical monomer
Two monomers coil together to form a coiled-coil dimer
Two dimers align in an anti-parallel fashion to form a tetramer
8 tetramers twisted into filament
What are the 4 major classes of intermediate filaments ?
- Keratin filaments
- Vimetin
- Neurofilaments
- Nuclear lamins
Describe keratin filaments
Keratin filaments in one cell link directly with filaments in a neighbouring cell through desmosomes
Found in hair, nails etc.
They provide mechanical strength and enable stretching.
Keratin mutants can cause cell rupturing in the epidermis because they cause the dermis and epidermis to separate.
Describe neurofilaments
They are found in neurons and provide mechanical support to the axon and help maintain its structure and stability
Describe nuclear lamins
They form the nuclear lamina, a mesh-like network that supports to nuclear envelope.
They are involved in the assembly/disassembly of the nuclear envelope: they are phorylated to cause disassembly during prophase.
What does a mutation in nuclear lamin A cause ?
Hutchison-Gilford Progeria Syndrome
Causes childhood onset of premature aging
How are the cytoskeleton components integrated in epithelial cells ?
- Actin filaments- Microvilli
- Microtubules- directed transport apical to basolateral
- Intermediate filaments- links to neighbouring cells and basal lamina
What is plectin ?
It cross links intermediate filaments into bundles.
It connect IF to microtubules and actin filaments.
It helps maintain structure.
SUN and KASH proteins allow communication between inside the nucleus and outside.
