Cytoskeleton Week 2 Flashcards
What is the cytoskeleton?
The skeleton and muscles of cells. It provides for architecture,shape and motility and for directed movement of organelles and molecules in the cell.
What are the components of the cytoskeleton?
Microtubules, Microfilaments, intermediate filaments and other accessory and regulatory proteins.
What is another name for microfilaments?
Actin filaments
What is the polymer of microtubulues?
Tubulin dimers (alpha and beta)
Tubulin is a ___________ meaning that is can turn _________ into __________
Tubulin is a GTPase meaning that it has the ability to turn GTP into GDP
How large is tubulin?
24nm
Where do microtubules stem from? What is the specific word to describe the orientation?
They stem out of the nucleus. Perinuclear
What are the accessory proteins associated with microtubules and what are their functions?
MAPs stabilize and space polymers and regulate interactions between cytoskeletal elements.
How dynamic are microtubules?
Highly dynamic if not stabilized
Microtubules act as a substrate for ___________
Microtubule based motor proteins to transport organelles. Think of the microtubules as the road and the motor proteins as cars.
Microtubules are ______________ which means that it has a ____ and ____ end. Which end is more dynamic?
Polarized , + and -. The + end lengthens and shortens more dynamically
What are the 5 functions of microtubules?
- Make up mitotic spindle
- Determine Cell Shape
- Provide railways for organelle transport
- Important for neuron cell shape and axonal transport
- Back bone for cilia and flagella
Which of the following are associated with microtubules?
Cilia, Flagella or Microvilli
Cilia and Flagella
Microtubules are composed of ___________ made of tubulin dimers. Describe this structure and how many are often found in a microtubule.
Protofilaments are stacks of tubulin dimers (alphabeta). Each microtubule has 13 +/- protofilaments.
What is used to determine the microtubule dynamic instability?
The behavior of the + end. Lengthening and shrinking is measured at the + end of the microtubule. When polymerization is occurring it is deemed “rescue” and when shortening is occurring it is called “catastrophe”.
Why does MT dynamic instability happen?
Tubulin, the dimer of microtubules, is a GTPase so it must be loaded with GTP prior to being polymerized. During elongation, a GTP-bound tubulins promote elongation and prevent the depolymerization of the microtubule. When the GTP-bound tubulin is hydrolyzed to GDP-bound tubulin, it removes this cap to promote shrinkage.
When does the GTP cap exist on microtubules?
During rescue or elongation
GDP-bound tubulin promotes elongation. Is this true or false?
False!
The ________ end of the microtubule is embedded in the nucleus.
Negative
_________ is negative end directed and ___________ is positive end directed. They both use ______ as energy.
Dynein, Kinesin, ATP
What are the two microtubule associated MOTOR proteins?
Dynein and Kinesin
What domain of motor proteins is attached to the mictrobule?
The head domain
____________ determines the type of cargo being carried by motor proteins and the rate of their activity.
Light and intermediate chains
What are examples of structural NON-MOTOR microtubule associated proteins?
Tau, MAP
What are the functions of non-motor microtubule associated proteins?
Organize MTs, Regulate MT stability and dynamics
What is nucleation?
The genesis of a cytoskeletal polymer
Where does nucleation of microtubules occur?
The centrosome.
__________ follows nucleation which is the elongation of the polymer
Polymerization
The centrosome is made of __________ perpendicularly aligned _________.
2 perpendicularly align gamma tubulins.
What is the purpose of gamma tubulins?
They are required for the polymerization of alphabeta tubulin dimers.
Where are gamma tubulins found in cells?
ONLY in the centrosome or other structures that nucleate, gamma tubulins are not part of the actual microtubule.
Cilia are located at ___________(organs). What is the function of cilia?
Lung epithelium, trachea and fallopian tube. They are mucociliary escalators which means they are found along airways to brush mucus out of the way.
Are cilia motile or non-motile?
They can be both!
The sperm tail is similar to __________. Why is this important?
It allows sperm to move towards the egg
Cilia and flagella do not originate from the nucleus. What is the nucleation site for cilia and flagella?
Basal bodies. Their negative end is in the plasma membrane as the positive end grows away from the cell.
Cilia and flagella are composed of ___________ in a __________ formation as _________. What is the name of this structure.
microtubules , 9+2 as doublets. Axoneme
___________ drives axonemal motility. Describe axonemal motility.
Dyenin allows for movement of the microtubule doublets in the axoneme structure to force the cilia and flagella to move.
________________ is a body-wide defect in axonemal structure that results in obstructive lung disease and __________. What structure is not functioning?
PCD/Immotile cilia syndrome, sterile males. The cilia is not functioning due to disruption in axonemal structure. This can prevent mucus from being removed from the lung epithelium and airways and also prevent sperm from traveling.
Combination of situs inversus and immotile cilia syndrome
Kartagener’s Syndrome; cilia are not functional during body development so cells move to wrong spots leading to irregular organ development.
How are microtubules being used to develop therapies for cancer?
Scientists are finding ways to disrupt microtubule dynamics to block cell division.
Mutations in _________ and _________ can result in smooth brain also known as ________.
L1S1 and doublecortin microtubule proteins, lissencephaly
What is Charcot-Marie Tooth syndrome?
It is a neuronal disease that has a mutation in kinesin.
How are neurodegenerative diseases related to microtubules?
Abnormalities or mutations in tau, dynein, kinesin and spastin
How can ________ viruses exploit a neuron’s microtubule based transport system to reach cell bodies?
Neurotropic
Virus will bind to the nerve ending of the cell to enter the body of the cell by catching a ride on a dynein motor protein towards the negative end of the neuron located in the cell body. Kinesin will then take replicated viruses back to the nerve ending to be transported to more cells for future replication.
What is the SMALLEST cytoskeletal element?
Microfilaments
What is another name for microfilaments?
Actin filaments
What are microfilaments made of and what is the arrangement?
Non-hollow polymers of the globular protein actin that is arranged in a helical structure!
Remember microtubules have tubulin dimers as their polymers
Actin is an ________.
ATPase
Remember tubulin is a GTPase
How large are microfilaments?
7mm in diameter
Microfilaments are ________ if not ________. They can undergo lots of assembly and dissassembly
highly dynamic , stabalized
Microfilaments act as a substrate for __________ of motor proteins. What is their function?
Myosin family of motor proteins to move along and carry cargo
Remember the motor proteins associated with microtubules are dynein and kinesin
Where are microfilaments nucleated compared to microtubules?
Microfilaments do NOT have a specific organizing center like the centrosome. They can be nucleated anywhere in the cell.
Are microfilaments polarized?
Yes! The barbed end is the “+” and and the pointed end is the “-“ end.
Which end of microfilaments are preferred for elongation?
The barbed end.
Which way is myosin directed on actin filaments?
Towards the barbed end (+) end.
What are the 5 functions of microfilaments?
- Various functions in cell cortex
- Cleavage furrow for pinching off cells
- Contraction of both muscle and non-muscle
- Cell motility
- Short range organelle transport
What are the 3 actin isoforms and what are they associated with?
Alpha: Muscle specific (cardiac,smooth and skeletal)
Beta and Gamma: Most cells
What is the general structure of actin?
A helical structure bound by accessory proteins.
What are the 3 ways actin filaments/microfilaments can be nucleated?
ARP2/3 Complex
Spire
Formins
Describe the ARP2/3 Complex. What does it nucleate?
The ARP2/3 complex nucleates actin filaments from already formed filaments by initiating a branched assembly on the sides of an existing microfilament. The ARP complex needs NPF (nucleation promoting factor) to do the nucleation. First, an ATP loaded actin binds to the NPF which is joined by the ARP2/3 complex. This structure can attach to the side of the actin filament, remove the NPF and continue building onto the branched filament.
What is one requirement of ALL actin filament nucleation?
ATP loaded Actin
What is one unique requirement of ARP2/3 system for nucleation?
NPF or Nucleation Promoting Factor
What is formin nucleation?
Formin binds 2 actin subunits in a linear fashion
What is spire nucleation?
Spire grabs actin in a linear fashion.
Which end does actin bind to during elongation?
Branched end
What happens to actin as the branch keeps building?
ATP bound actin is required to add onto the branched end of a microfilament. However, as new ATP-bound actins are added, previously added actins loose a phosphorous to become ADP-bound actin.
Where is nucleation of microfilaments generated from?
Pointed end of actin filament.
How do myosin play a role in contractility and intracellular transport?
…
In a sarcomere, how are the pointed and branched ends of microfilaments arranged?
The pointed ends are furthest from each other and the barbed ends overlap each other in the middle.
What is the general structure of myosins?
A head(s) and light chains.
What are 3 types of Myosins?
Myosin 1, 2 and 5.
Which myosin generates ALL the movement and is most common? What feature of this myosin allows for its function?
Myosin 2. It has a Calmodulin light chain which are calcium binding proteins that determine if myosin will move.
What are myosin light chains? Which myosins have them and what is their purpose?
On-off switch for the myosin that binds calcium. Myosin 1 and 5 have calmodium light chains while Myosin 2 has a regulatory and essential light chain.
What are myosin regulatory light chains?
Is phosphorylated and dephosphorylated to control myosin movement. They are controlled by kinases.
Which two polymers are involved in cytokinesis?
F-actin and Myosin II
__________ are microfilament actin based _________ projections
Microvilli, epithelial
What is one function of microvilli?
Increase surface area for absorption during digestion.
What are stereocilia? Are the microtubules or microfilaments?
Stereocilia are found in ear cells to detect sound waves. They are actin filament based and thus MICROFILAMENTS
Describe the structure of a microvilli. What is the function of myosin in this structure? Which myosin is used?
Long actin filaments extend from the terminal web up towards the surface of the skin. The barbed end is always pointed up. Myosin 1 with calmodium light chains hold actin filaments by binding the terminal web in the membrane. They have NO motor function in this structure.
The ______________ of which myosin is bound to the microvilli?
Hydrophobic lateral arm (calmodium) of myosin I binds to microvilli.
What stabilizes the microarray of actin filaments forming the microvilli?
Villin and fibrin
The physical link between the ECM and the cytoskeleton is a _________ which provides for ________.
Transmembrane protein, mechanical continuity
What is the name of the disease that deforms red blood cells to fragile _________ because of weakened binding affinity of spectrin to Band 4.1?
spherocytes, Hereditary Spherocytosis
What is a erythrocyte cytoskeleton made of?
Spectrin tetramers, and Actin. The actin forms a scaffold for the spectrin web.
How is breast cancer related to actin?
Sometimes, the actin associated protein Tinesin disrupts the linkage of integrin receptors to the actin cytoskeleton causing migration of cancer cells.
What is the name of the disease that deforms RBC’s to fragile elliptocytes because of ___________?
Hereditary Elliptocytosis, incomplete formation of spectrin
A mutation in ______________ can cause _________ which is characterized by an enlargement of the heart muscle/
Actin alpha, Familial Hypertrophic Cardiomyopathy
Mutations in ________ can cause deafness
Myosin VI ; stereocilia are affected
Mutations in Myosin VII can cause __________.
Deafness, neurological issues, blindness (Usher Syndrome Type 1)
How do pathogens use actin machinery to take advantage of the host?
Pathogens will develop surface proteins similar to actin nucleation molecules which induces the formation of an actin tail. The pathogen now motile is able to push it self out of one cell into the next.
What is an example of a pathogen that uses actin machinery to infect?
Listeria monosytogenes
What does Phallodin do?
Phallodine IRREVERSIBLY binds to actin filaments and stabilizes them.
What is the class of cytoskeletal elements that are molecularly related but diverse?
Intermediate Filaments
Are intermediate filaments polarized?
No!
How big are intermediate filaments?
10 nm
Are intermediate filaments dynamic?
NO, much more stable
What are the 4 functions of intermediate filaments?
- Space filling elements to increase cell volume
- Give cell tensile strength
- Specialized functions such as serving as cell markers
- Important at cell junctions
How conserved are intermediate filaments compared to microfilaments and microtubules?
Less conserved
What is the nucleation process of intermediate filaments?
They don’t have one! They just polymerize. Two IF monomers will form a coiled dimer. Two dimers will then form an ANTIparallel tetramer that can stack up to 8 times for one full IF. The filaments get longer and wrap into a rope like structure.
What region is shared by all intermediate filaments. Which is not?
The alpha region aka the non-central portion of the filament is all the same. The central portion of each intermediate filament varies and is the portion that will interact with to form the 8 tetramer stack.
What type of cytoskeletal element are keratins and where are they found?
Intermediate filament, epithelial cells, hair, nails
Nuclear lamins are _________ and are found in ________.
Intermediate filaments, nuclear lamina of ALL nucleated cells
What condition is characterized by skin that is very sensitive to mechanical injury? Which layer of the epidermis does the mutation of the _______ gene occur?
Epiderolysis bullosa simplex
Basal cell layer
Keratin
What disease is characterized by fast aging in young children? What is affected? Is it fatal?
Nuclear Lamin protein is mutated resulting in Progeria. It is fatal
How many diseases are associated with the IF family?
76
How many IF diseases in keratin mutated in?
Over 20
What is desmin ? If it is mutated, what can result?
Intermediate filament that is mutated in cardiomyopathies
What is mutated in Charcot-Marie Tooth disease?
Neurofilament proteins
What is peripherein?
It is an intermediate filament induced after peripheral nerve injury for repair.
What disease is characterized by abnormal myelin? What is mutated
Alexander disease, Glial fibrillary acidic protein is mutated.
