What are the 3 main types of cytoskeletal elements in eukaryotic cells?
What cytoskeletal elements are made from alpha and beta tubulin subunits?
What cytoskeletal elements are made up of actin monomers?
What cytokeletal elements emanate from a single organizing center within interphase cells?
1. Positioning organelles within the cell 2. Transport of vesicles for intracellular trafficking 3. Partioning of chromosome during division
What are the functions of microtubules?
What cytoskeletal elements determines cell shape and ae involved in whole cell movement?
What cytoskeletal element is a large and heterogenous family of proteins and provides mechanical strength?
The cytoskeleton provides the cell its what?
The cytoskeleton allows for cellular remodeling during periods of what?
The cytoskeleton is used for what? (It includes swimming and crawling)
What is the cytoskeleton used for during mitosis?
What kind of trafficking does the cytoskeleton drive?
The cytoskeleton provides what kind of support to the plasma membrane?
Muscle contraction and axon/dendrite extension in neurons
The cytoskeleton provides the machinery used for what?
Generates and/or maintains organelle structure
The cytoskeleton does what for organelle structure?
Dynamic and adaptable
Are cytoskeletal elements static and unchangeable or dynamic and adaptable?
The needs of the cell
Changes to the cytoskeleton depend on what?
Individual subunits of the cytoskeleton in a constant state of what?
Just beneath the plasma membrane
Where are actin filaments found?
Strength and shape
Actin filaments provide what to a cell?
Lamellipodia or filopodia which are essential for cell motility
During interphase, the actin filaments beneath the plasma membrane form dynamic structures called what?
Lamellipodia or filopodia are essential for what?
Actin has a polarized organization in what kind of cells?
What exists as long filaments that project from the microtuble organizing center which is located adjacent to the nucleus?
The structural organization of microtubule and actin filaments undergo dramatic changes when the cell undergoes what?
The mitotic spindle
After chromosomes duplication the single microtubule array will form a bipolar structure called what?
The mitotic spindle is essential for the segregation of what?
Actin structures formed for motility will do what to prevent cell movement?
The contractile ring
Actin will reform, with the help of associated motor proteins, to form a 'belt' around the middle of cell called the what?
Microtubule-dependent chromosome segregation
The contractile ring will 'pinch' the cell in half after what?
The cytoskeletal filaments
What will reassemble to form the structures first described in interphase?
Bundles of actin filaments form what to increase the cell surface area thereby increasing nutrient uptake?
Are actin filaments stable structures or instable structures?
Do microvilli have a constant location, length and diameter or variable location, length and diameter?
The contents of the intestinal lumen from leaking into the body
Actin filaments also form below the microvilli; these cell-cell junctions prevent what?
Actin and microtubule filaments have what? It enables cells to differentiate between top and bottom and left from right.
In polarized epithelial cells, microtubules run vertically (apical to the basal) or horizontally which is important for the trafficking of newly synthesized material?
Intermediate filaments, attached to what, link adjacent epithelial cells together to form a sturdy sheet of cells
A sturdy sheet of cells
Intermediate filaments, attached to desmosomes, link adjacent epithelial cells together to form what?
Intermediate filaments, attached via what, link epithelial cells to the underlying extracellular matrix on the basal lateral side of the cell?
The underlying extracellular matrix on the basal lateral side of the cell
Intermediate filaments, attached via hemidesosomes, link epithelial cells to what?
1. They provide dynamic structures for cellular reorganization, 2. They are stable structures for the maintanance of cellular structure 3. They establish polarity in a cell
Name three functions of cytoskeletal elements
α- and β-tubulin (γ tubulin also exists)
Microtubules are formed from two tubulin subunits (dimers); What are they?
α- and β-tubulin subunits are tightly bound to each other as a what?
Each tubulin monomer (α- or β-tubulin) binds to one molecule of what?
Hydrolysis; (α-tubulin always has GTP bound)
Organization of the tubulin heterodimer is such that the GTP bound to the alpha subunit is protected from what?
Hydrolysis; (β-tubulin can have either GTP or GDP bound)
GTP bound to the beta subunit can undergo what? (This effects MT dynamics)
α-tubulin always has GTP bound and β-tubulin can have either GTP or GDP bound. This difference is important for the property known as what?
What are hollow tubes formed by 13 protofilaments containing alternating α- and β-tubulin heterdimers?
Microtubules are stiff and difficult to bend due to what kind of interactions?; This makes MT the straightest structural element in cells (up to millimeters in length!)
Tubulin subunit assemble into what in the same direction giving the microtubule a distinct polarity.
At the other end
Tubulin subunit assemble into a protofilament in the same direction giving the microtubule a distinct polarity; α-tubulin subunits exposed at one end and β-tubulin subunits exposed where?
The minus end
Microtubule end with the free alpha subunit is called the what end?
The plus end
Microtubule end with the free beta subunit is the what end?
Microtubules nucleate from the microtubule organizing center (MTOC) located near the what?
Microtubules nucleate from the microtubule organizing center located near the nucleus. This sets up polarity such that all microtubles are "what"?, that is the plus ends of the microtubule emanate outwards from the center of the cell
The microtubule organizing center
All minus ends are embedded within what?
All eucaryotic cells
What kind of cells is tubulin found?
Tubulin is highly what?
Yeast and human tubulin share what percentage of amino acid sequence identity?
6 isoforms (each of alpha and beta tubulin)
There are multiple isoforms of tubulin: how many isoforms are in humans?
Each isoform has a distinct location within the cell and performs subtly different what?
Actin monomer subunits
Actin filaments are composed of what kind of subunits?
ATP (or ADP)
Actin subunits bind what?
A head-to-tail fashion
Actin subunits assemble in what fashion to generate a filament with polarity?
To the "minus end" of the actin filament
ATP binds in a deep cleft in the center of an actin monomer which is open to what end of the actin filament?
The 'pointed end'
The "minus end" of the actin filament is what?
The 'barbed end'
The "plus end" of the actin filament is what?
Pointed versus barbed nomenclature refers to the arrowhead appearance of what heads when bound to actin filaments?
Actin filaments are a single helix of monomers that forms what looks like two parallel protofilaments that twist around each other in what kind of helix?
They are typically crosslinked by accessory proteins making actin structures stronger than an individual filament
Why are actin filaments flexible and easily bent, but strong?
Plasma membrane (cell cortex)
Actin filaments are nucleated at the what?
What kind of cells do you find actin filaments?
(Extraordinarily well) conserved
Actin is what?
The amino acids sequence of actin from different organisms are what percentage identical?
Alpha, beta, and gamma
What are the three different isoforms of actin in vertebrates?
1. They differ only slightly in their amino acid sequence 2. The alpha isoform is expressed only in muscle cells 3. The beta and gamma isoforms are found in nonmuscle cells
What are the differences between the three isoforms of actin?
What kind of filaments are only found in some metazoans including vertebrates, nematodes, and mollusks but not in all cell types of these organisms
Cells subjected to mechanical stress
Intermediate filaments are prominent in the cytoplasm of what kind of cells?
A rigid exoskeleton
Intermediate filaments are not found in animals that have what kind of exoskeleton?
Cytoplasmic intermediate filaments are closely related to what?
What form the meshwork beneath the inner membrane of the nuclear envelope and are the site of chromosome and nuclear pore complex attachment?
The individual polypeptides of intermediate filaments are elongated molecules with a central α-helical domain that assemble to form what?
The individual polypeptides of intermediate filaments are elongated molecules with a central α-helical domain that assemble to form parallel dimers. Dimers associate in a staggered antiparallel manner to form what?
Since tetramers are composed of antiparallel dimers, intermediate filaments do not have what?
How many tetramers assemble in a laterally manner to form a rope like filament?
Intermediate filaments have a rope-like characteristic making them easily bent but extremely difficult to what?
For what, phosphorylation may have a role in triggering their disassembly similar to what is seen for nuclear lamins during mitosis?
Actin or microtubules
The intermediate filament family is more diverse than what?
What is the most diverse family of intermediate filaments?
How many different keratins are there?
How many kinds of keratins are found in human epithelial cells?
How many kinds of keratins are found in hair and nails?
Anchoring the intermediate filaments at sites of cell-cell contact sites
How do keratin filaments impart mechanical strength to epithelial tissues?
Human genetic disease
Keratin gene mutations have been linked to what?
Defective keratin molecules can result in what in response to minor mechanical stress?
Blisters are due to rupturing epithelial cells as a consequence of what?
along the axons of vertebrate neurons
Where are neurofilaments found in high concentrations?
NF-L, NF-M and NF-H
What are three types of neurofilaments?
NF-L plus either NF-M or NF-H
NF-L, NF-M and NF-H can coassemble in vivo to form what?
During axonal growth, new neurofilament subunits are incorporated along the what?
At the ends of neurofilament polymers and along the length of a filament
Filament addition occurs where?
What kind of addition increases the diameter of the axon?
Neurofilament gene expression
Axonal diameter is controlled by what, which influences how fast an electrical signal travels down the axon?
ALS or Lou Gegrig's desease
Mutations in neurofilament genes that impact filament assembly have been linked to what disease?
Abnormal assembly of neurofilaments in motor neurons and in the axon interferes with normal axonal transport leading to what?
The assembly and disassembly of actin and tubulin
Eukaryotic cell survival depends on the balance between what two things?
By plants, fungi or sponges
Toxins that specifically target actin and microtubule filaments are produced in self-defense by what (they can not run away from predators)?
Either filament formation or its disassembly
The toxins produced bind tightly to either the filament form or the free subunit forms to drive what opposing actions?
Latrunculin and swinholide
What two toxins (from different marine sponges) depolymerize actin filaments by binding to actin subunits to prevent their assembly or severing actin filaments?
What toxin (fungal metabolites) binds to the plus end of actin filaments to prevent actin polymerization?
What toxin ("death cap" fungus) stabilizes actin filaments by binding at the interface between actin subunits?