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What are the three major classes of filament in a eukaryote cytoskeleton?
Microtubules, microfilaments (aka actin filaments) and intermediate filaments
Which two filaments are polar and which is non-polar?
Microtubules and microfilaments are polar, intermediate filaments are non-polar
What are microtubules composed of?
Tubulins
What is the diameter of a microtubule?
25nm
What are microfilaments composed of?
Actin
What is the diameter of a microfilament?
7nm
What is the diameter of an intermediate filament?
10nm
What is the composition of an intermediate filament?
Intermediate filaments are composed of various proteins, including keratins, vimentin, and neurofilaments, depending on the cell type.
Which part of the cytoskeleton do colchicine and taxol affect?
Microtubules
Which part of the cytoskeleton do phalloidin and cytochalasins affect?
F-actin
Give a brief overview of indirect immunofluorescence light microscopy
A technique used to visualize specific proteins in cells or tissues using antibodies that are tagged with fluorescent dyes. Example: if you want to study actin from a mouse cell, the actin is injected into a rabbit and the rabbit’s antibodies are purified. Then secondary antibodies are obtained from a sheep and loaded with GFP. The secondary antibodies bind to the primary antibodies, allowing visualization under a fluorescence microscope.
What is polyacrylamide gel electrophoresis (PAGE) used to investigate the cytoskeleton?
A method for separating polypeptides on the basis of their different relative molecular mass. A protein gel of polymerised acrylamide is used for comparing samples (eg. lung vs liver cells).
What are the four functions of microtubules?
Cell shape and polarity, cell organisation and positioning of organelles, cell division, cell motility
In cells, tubulin exists as a heterodimer. What does this mean?
An alpha and beta tubule are bound together as a heterogenous dimer.
How many protofilaments make up the wall of a microtubule with a lumen in the middle?
13
Which is the growing end of a microtubule?
+
What is another word for the MTOC (microtubule organising centre)?
Centrosome
Describe the structure of the centrosome
A pair of centrioles surrounded by pericentriolar material from which the microtubules grow
What is colchicine used for in relation to the cytoskeleton?
It is used to disassemble the microtubule and then it can be observed regrowing
What does taxol do in the cytoskeleton?
Overstabilizes microtubules and prevents their disassembly.
What are MAPs in the cytoskeleton?
Microtubule-associated proteins.
What do microtubule-associated proteins do?
Link microtubules to each other, link mts to the cell membrane, link mts to vesicles (they ‘walk‘ vesicles along the length of the tubule) or control mt assembly and disassembly
What is another name given to microfilaments?
Actin filaments
What is a stress fibre?
A bundle of actin fibres which are contractile (ie myosin helps them to contract)
Where are actin filaments found in the cell
They run parallel to the cell surface on the interior and also mechanically linking the sides of cells in adherens junction and in brush borders of microvilli
What do actin filaments do?
They are important for morphogenesis, mechanotransduction, cell-cell adhesion and cell membrane adhesion
What are G-actin and F-actin?
Globular actin (monomer) and fibrous actin (polymer)
From what plant is the toxin phalloidin obtained?
Death cap mushroom
What does cytochalasin do to actin?
Depolymerizes it
What does phalloidin do to actin?
Overstabilises actin
What is the most abundant protein in a cell?
Actin
What is actin treadmilling?
When actin is simultaneously polymerising and depolymerising from opposite ends. The role of this phenomenon is unclear.
What type of proteins regulate the function of actin?
Actin-binding proteins
What is the basic common structure of intermediate filaments?
Very fibrous and rich in alpha helices, stable and non-polar
Which component of the cytoskeleton is used to diagnose spina bifida?
An increase in a type of intermediate filament called GFAP from amniotic fluid
Which tissue type is the protein lamin found in?
Nuclear lamina in eukaryotic cells
Which tissue type is the protein vimentin found in?
Cells of mesenchymal origin
Which tissue type is the protein keratin found in?
Epithelial cells and derivatives
Which tissue type are neurofilaments found in?
Neurons
What is meant by cell integrity?
The complete and unharmed state of a cell wall
How many genes do humans have for keratin?
At least 30
What is hyperkeratosis and what type of keratin does it effect?
A thickening of the skin, affecting ker1 and ker10
What is epidermolysis bullosa simplex and what type of keratin does it effect?
A group of rare inherited skin disorders that cause the skin to be fragile and blister easiy, affecting ker14
What is pemphigus vulgaris?
A group of autoimmune diseases causing blisters on the skin and mucous membranes throughout the body
