Cytoskeleton Flashcards
how many polymers are there?
3
-actin filament, microtubules, intermediate filaments
what is the function of the cytoskeleton?
structure of cell, intracellular movement of organelles, cell movement
is the cytoskeleton dynamic?
- yes
- polymer ⇌ monomer
what so accessory proteins regulate?
- site + rate of filament formation
- polymerisation, depolymerisation
- function of cytoskeleton
describe the structure of microtubules and their function
- hollow tubes made of tubulin
- rigid, long and straight
-organelle positioning, intracellular transport, cell movement
describe the structure of intermediate filaments and their function
- heterogenous groups of filament proteins
- rope like structure
-gives mechanical strength to the cell
what is another name for actin filaments?
microfilaments
describe the structure of actin filaments and their function
- helical polymers made of actin
- flexible, organised into 20 networks and 3D gas
-cell and organelle shape, cell migration
give 2 properties of the polymers that make up the cytoskeleton
- monomers are abundant
- not covalently bonded
describe the structure of actin
- twisted chain units of G-actin to form F-actin
- provides structural polarity
- associated w’ actin-binding proteins (ABP)
what are the 3 isoforms of actin
- α-actin found in muscle cells
- β and γ actin found in non muscle cells
how can actin polymerise?
-by the addition of g-actin to the f-actin
how are g-actin levels controlled?
mainly by ABP
- thymosin β4: prevents addition of G-actin
- profilin: facilitates actin polymerisation
what are the 2 ABPs that bind to f-actin?
1) actin bundling proteins
- parallel bundles
- eg: microvilli in epithelial cells
2) cross linking proteins
- maintain f actin in gel like network
- eg: cell cortex
what do f actin severing proteins do?
break f actin into smaller filaments
what do motor proteins do?
transport of vesicles and organelles through filaments
how is actin arranged in skeletal muscle?
- para-crystalline array integrated w diff ABPs
- interaction w rosin allows muscle contraction
how is actin arranged in non muscle cells
- cell cortex: form a thin cheat beneath plasma membrane
- associated w myosin: form a purse string ring that results in cleavage of mitotic cells (cytokinesis)
explain the process of cell migration
- cell pushes out protrusions at its front to show the route
- causes actin polymerisation: the accumulation of f actin
-protrusions adhere to the surface and interns link
filaments to extracellular matrix around cell
-cell contraction and retraction of rear part of the cell
describe the structure of intermediate filaments
- toughest of the cytoskeleton filaments
- rope like made of many strands twisted together
- form a network throughout cytoplasm, joining up to cell to cell junctions
- surrounds the nucleus
explain the polymerisation of intermediate filaments
- each unit has an N terminal, C terminal globular protein and central elongated ‘ rod-like’ domain
- units for 2 stable dimers
- every 2 dimers form a tetramer
- tetramer bind to each other to make rope like filament
what are the two types of intermediate filaments?
nuclear and cytoplasmic
what are nuclearlamins?
- nuclear filaments
- forms ‘mesh’ structure
- line inner face of nuclear envelope to strengthen + provide attachment sites for chromatin
- disassemble + reform at each cell division controlled by post translational modifications (de/phosphorylation)
what are the cytoplasmic filaments?
- keratins in epithelia
- vimentin in connective tissue, muscle cells and neurological cells
- neurofilaments in nerve cells
what do the cytoplasmic filaments do?
- provide tensile strength so cell can withstand mechanical strength
- structural support by creating deformable 3D structural network to reinforce cell shape and organelle localisation
describe the structure of microtubules
- hollow tubes makes of ruby lim
- each filament is polarised
- dynamic structure so can assemble and disassemble in response to cell’s needs
what are MTOCs?
microtubule organising centres
- specialised protein complexes where assembling of tubulure units start
what is the MTOC in most cells?
centrosome
- contains γ tubulim ring that initiated microtubule growth
what are the monomers of microtubules?
- α and β tubulin that form heterodimers in a polarised growth
what is the function of microtubules?
1) intracellular transport: acts as a railway which molecular motors run different motors for diff cargoes
- directionality of filaments is vital
2) organised position of organelles: provides polarity
3) rhythmic beating of cilia&flagella: motile processes w highly organised microtubule core
- 9+2 structure: axoneme
- bending of cilia & flagella is driven by motor protein dynein
- basal body at base of tubule controls assembly of axoneme
