Cytoskeleton Flashcards
What are some characteristics of the cytoskeleton?
It enable cells requirement to be pulled apart yet maintain orientation (its top and bottom), functions and remodelling
It is filamentous, where all the filaments interact.
This allows it to be strong enough to resist physical stresses on cells
and flexibile.
Dynamic response to growth signals
It is reliabile with excess capacity, genetic redundancy
Why do cells require to be pulled apart yet maintain orientation
1) mitosis
2) migration (caused by polarisation of actin pushing force)
3) specific cell shape in differentation and as part of a tissue.
What are the systems of the cytoskeleton?
1) ACTIN microfilaments
2) Tubulin microtubules
3) Intermediate filaments
Describe the orientation of the systems in an POLARISED epithelium cell.
Actin act as (smallest) stress fibers and induce movement
Tubulin microtubules like a spindle where SINGLE filaments spread to perifery of cell and out into lamella
Intermediate filaments present in crosslinked bundles to form flexible net structure.
All interact with each other throughout the cell and all are attached to the basement membrane.
Which system can be found connected with adjacent cells.
Actin microfilaments forming contacts and adhesions. Intermediate filaments also integrate between tissues.
Microtubules are not associated with junctions.
Name examples o signals that may act to regulate the cytoskeleton. What effect might happen?
1) Growth factors
2) Cytokines
3) Matrix components
External signal may cause the filament subunits to disassemble, diffuse then reassemble at a new site.
Describe the effect of thermo and mechanical stress on different types of filaments.
Single protofilaments like ACTIN prone to stress/unstability as there are no bonds between filaments, only subunits on the same filament.
Microtubules more resistant as there are bonds between subunits and other filaments.
Intermediate even more stable with ROPE properties; staggered bonds means it can be disorted without being broken.
How can cells be motile?
By having a dynamic cytoskeleton that can distort cell shape and move forward (also sensing function)
The properties of ACTIN
4-6nm (smallest)
very dynamic
Polar as there are two different ends
meshwork/bundles
Can be remodelled by ATP
The properties of tubulin
25nm (biggest)
EXTREMELY dynamic
Polar
Singular tubules
Can be remodelled by GTP/GDP
The properties of Intermediate filaments
10nm
Stable
APOLAR
Exists in bundle
Can be remodelled by phosphorylation
Give examples of specialised cells and how the cytoskeleton is used.
Muscle cells Contraction machinery (ACTIN); supporting shape changes
Epithelia
Polarisation (TUBULES); barrier formation
Neurones
Polarisation; supporting extreme shapes
Glial cells
Maintaining directed cell extensions structurally (INTERMEDIATE)
Sensory cells
Polarity; cell shapes (ACTIN/TUBULES)
Describe the cytoskeleton in the microvillus
(in the small intestine cells maintain orientation of absorbing brush border of the villus
ACTIN filaments are crosslinked and to the membrane to make this more stable.
Linking proteins include, villin and fimbrin between filaments and mysoin1 and calmodulin between the filaments and the membrane.
Give examples of specialized cells
1) the photoreceptor (transported through cell)
2) cochlear hair cells (picks up vibrations and is ACTIN based)
3) skeletal muscle cells (contraction)
4) Epitheal cells (wound healing)
What is the leading edge of a crawling cell?
lamellipodia are ribs of actin called microspikes, which, when they spread beyond the lamellipodium frontier, are called filopodia which have exploring functions
This formation of actin filaments “push” the leading edge forward and is the main motile force for advancing the cell’s front edge giving CELL MIGRATION.
This is acheived by POLARISED actin distribution in moving cells. For example in the filopodium, actin is in a tight parallel bundle but in the internal cell it is a gel network.
Actin determines cell shape for cell processes.
Actin distorts membrane/cell to allow engulfing of bacterium and therefore allows phagocytosis.
If cells are adhesive and spread out they are more likely to enter the S PHASE in division.
Involved in neuronal growth through the actin production of cone-lamellipodia and filopodia
Involved in Actin-dependent dendritic spines-memory; memory based on the growth of spines over time
Explain the problem of intracellular transport in neurones.
It has fine axons that are prone to damage that have to transmit important messages over long distances however, intermediate strengthen these.
How is the problem of transport solved?
CELL MOTORS which transport vesicles along filaments such as microtubules.
There are different kinds of motors; in axons microubules broken up with lots of short distances for the cargo to be carried along parts of the axon and connected dendrites forming is pathway
Fibroblasts have single longer tubules with longer pathway
Name two types of MOTORs that transport organelles
1) Dynein
2) Kinesin
What is an adhesion belt’s role in the cell?
Adhesion belt is associated with ACTIN filaments and allow the whole sheet of cells to move not just a single cell.
An organised tightening of this belt in selected regions causes a pocket to be produced, for example an epithelial tube.
List junction ound betwen cells
1) Adherins CELL TO CELL or Cell to MATRIX. attached by ACTIN
2) Desmosome attached by INTERMEDIATE
3) Hemidesmosome attached by INTERMEDIATE
What cytoskeleton genes are involved in cancer?
Adhesion (cadherins) and signalling (ras) oncogenes.
What cytoskeleton genes are involved in disorders if MUTATED?
What are these disorders?
Haemolytic anaemia (spectrin)
Skin fragility disorders (keratins)
Motorneurone disease (neurofilaments)
Cardio- and skeletal myopathies (desmin)
Progeria (lamin)
Male sterility (tubulin)
Deafness, blindness (myosin and kinesin-type motors)
How has knowledge about the cytoplasm helped fight disease (cancer)?
Drugs can be made specific to actin or microtubules.
For example Phalloidin binds to and stabilises actin.
Taxol does the same to microtubules; it changes the dynamics of the tubules and therefore prevents tumour genesis.
What are the key components of the cytoskeleton?
Filaments:
Intermediate filaments,
Microfilaments (made of actin),
Microtubules (made of tubulin).
Associated proteins:
Motor proteins
Linkers
Modifying proteins
Membrane binding sites:
Attachment proteins
