Cytoskeleton Filaments Flashcards
Name the 3 major filaments in cytoskeleton
Intermediate filaments
Microtubules
Actin filaments
What are the major functions of the cytoskeletal filaments
Facilitate cell movement and also maintain shape
Where are intermediate filaments located
Cytoplasm and nucleus
What are cells/intermediate filaments linked by
Desmosomes (proteins)
What are intermediate filaments called when in nucleus and what is their job in nucleus
Nuclear lamins
Form mesh along inner membrane to act as anchors for chromosomes and pores
Explain the structure of IF from monomer to tetramer
A- helical monomer which forms a coiled dimer when 2 helixes
Then the tetramer means 4 A helical strand (2 coiled dimers)
What is assembly and disassembly of IF regulated by
Phosphorylation (ATP)
What are the subunits called which make up the nuclear lamins
Lmna Lmnb LmnC
What happens to IF in cell division
Phosphorylated to segregate the nucleus
The protein domains of IF differ between each area /cell of body
Eg keratin, neueofilaments, nucleus
What does this allow
Determination of source of tumours
Where are microtubules found and what’s their role
Cytoplasm (grow from centromere)
Function is division of chromosomes
Shuttling of vesicles in cytosol
Facilitate cilia movement
What are the monomers of microtubules called and how are they built up
Tubulin monomers
Built and dissembled by GTP
Why are microtubules found in ciliated cells extending from basal body?
They facilitate cilia movement
Explain the full structure of microtubules
Made of tubulin heterodimers which include both Beta and Alpha
Tubulins form protofilaments
There are 13 protofilaments giving the tube like structure
They have a plus end (beta) and a negative (alpha)
What does it mean that microtubules have polarity
The plus end is Beta groups
The minus end is alpha - this is where they break down
What are the 2 motor proteins found attached to microtubules to carry cargo?
Dynein
Kinesin
What do kinesin and Dynein motor proteins use to move across microtubules
Atp hydrolysis (when atp is bound to their globular heads)
Which end does dynein and kinesin move cargo to
Dynein = minus
Kinesin = plus end
What does the cargo carried depend on for dynein and kinesin
Their tail shape
How are cilia arranged (in terms of microtubules and dynein)
9 doublets (a,b microtubules) 2 singlets joined by nexins
Moved by dynein arms
What if nexins didn’t join singlets
Dynein would cause sliding in the tubules and wouldn’t be able to bend
What is actins job
Cell contraction and preventing too much stretch
Cell movement
Keep microvilli upright
Explain actin filaments structure
2 stranded helix which is coiled
37nm
What do actin filaments use to build/disassemble
ATP hydrolysis (phosphorylation)
Why is actin found in microvilli
Keeps the microvilli upright
When actin is in high concentrations in cytoplasm what do they form
Cross linked bundles
Actin is polar because it has a - end and a + end. Why does the + end grow rapidly
Due to Globular actin monomers
There are 6 actin binding proteins. Name them
Myosin motor proteins Bundling proteins Severing proteins Cross linking proteins Side binding proteins
What do severing proteins do to actin filaments
They fragment them to form a fluid state
What do bundling proteins do
Hold actin filaments in a gel mesh network in the cortex for example for microvilli support
What do myosin motor proteins do
Form contractile bundles with actin
Actin filaments cause cells to move across surfaces. First step is protrusion explain it
Actin polymerisation at the + end pushes the membrane of the cell forward
Forms protrusion (new actin cortex)
Explain the next step after protrusion of cellular movement
New Anchorage points form at the new actin cortex (protrusion) which allows movement across the cell
Contraction of myosin motor proteins at the end of the cell pushes it forward
What are myosins and what is their job
Motor proteins which move vesicles or membrane via their tails
Globular heads which use ATP hydrolysis to move are attached to actin filaments
Which type of myosin moves membranes and vesicles?
Myosin I
What does myosin II do
It slides actin filaments past one another using the globular heads in muscle contraction
Spectrin is another cytoskeleton protein in inner membrane of cells. Explain the structure and function
Tetramer of spectrin is bound to actin molecules in a pentagon structure
This allows stability and cell shape to be maintained
What 2 reasons are there actin associated proteins
For regulation / polymerisation
For movement - eg
Motor myosins
Name the 4 types of intermediate filaments and where found
Nuclear lamins
Keratins filaments (eg in skin,nails)
Vimentin- muscle
Neurofilaments- in neurones
What is keratins IF job
Found in cytoplasm of cells stuck to desmosomes and prevent excess stretching and rupturing of cells
What is IF job in neurofilaments (neurones)
Determine axon diameter and provide neurone strength
What is IF job in vimentin (muscle)
Lines the sarcomere and prevents muscle fibre misalignment
What is an example of where bundling proteins bundle actin together
Microvilli support
Where is cross linking protein action found in actin
In spectrin network in RBCS
