Cytoskeleton and cellular motility - Week 25 Flashcards
what is the function of cytoskeletons
The cytoskeleton provides a structural framework for cells to maintain and change shape, attach to surfaces, and perform various cellular tasks. These tasks include transporting organelles and vesicles, dividing the cytoplasm, specializing cell surfaces, and enabling cell motility.
What are the roles of actin filaments in eukaryotic cells, including their contributions to plasma membrane organization and microvilli formation and function?
Actin filaments: form cytoskeletal and motility systems in all eukaryotes.
Crosslinked actin filaments resist deformation, transmit forces, and restrict diffusion of organelles.
Cortical actin filaments: network that excludes organelles, reinforces the plasma membrane, and restricts the lateral motion of some integral
membrane proteins. The cortex varies in thickness from a monolayer of actin filaments in red blood cells to more than 1 µm in amoeboid cells.
Microvilli (filopodia): expand the cell surface for transport of nutrients and participate in sensory processes, including hearing. Bundles of actin filaments support microvilli.
How do actin, microtubules, and intermediate filaments work together to support cellular functions, such as intracellular transport and cell division
The actin cytoskeleton interacts with microtubules and intermediate filaments, supporting various cellular functions such as intracellular transport and cell division. These structures complement each other and work together to provide structural support and enable cell motility.
where does actin filaments undergo rearrangements during cell migration
The Lamellipodium is the site where actin filaments undergo rearrangements during cell migration.
what are the 2 ways that actin helps with cell movement
Actin plays a crucial role in cell movement through two mechanisms. Firstly, the polymerization and depolymerization of actin filaments generates the force required for cell migration. Secondly, actin provides tracks for myosin motor proteins to move along, which drives the movement of the cell.
How are actin and myosin filaments involved in cellular processes such as muscle contraction, cell division, and providing structural support through the formation of contractile muscle fibers and stress fibers
Actin and myosin filaments are involved in various cellular processes, including muscle contraction and cell division. They form stable contractile muscle fibers, a contractile ring during cell division to separate two daughter cells, and stress fibers in conjunction with other proteins to provide structural support and enable cellular contraction.
what does the process of actin polymerization use as the source of energy
The process of actin polymerization, in which actin monomers assemble into filaments, requires ATP (adenosine triphosphate) as an energy source.
what does actin binding protein play a role in regulating
Actin binding proteins play a crucial role in regulating the assembly, disassembly, and organization of actin filaments in cells.
what are some specific functions of different actin binding proteins
Different actin binding proteins have specific functions such as binding actin monomers, severing filaments, capping filament ends, nucleating filaments, promoting polymerization, crosslinking filaments, stabilizing filaments, or moving along filaments.
what are the different types of actin binding proteins with examples
- Bind monomers: Profilin, B-thymosin, cofilin
- Actin filament nucleating: Arp2/3 complex (activated by WASP)
- Actin filament polymerases: Formins
- Actin filament capping proteins: Gelsolin, Heterodimeric capping proteins
- Actin filament severing proteins: Cofilin, formins, fragmin, severin
- Proteins that bind the side of actin filaments: Tropomyosin, fimbrin
- Actin filament crosslinking proteins: Alpha-actinin, filamin
what is critical for lamellipodium
Actin is critical for the lamellipodium, the leading edge of a migrating cell.
What are some examples of actin filament destabilizers, and how do they destabilize actin filaments
Actin filament destabilizers include Latrunculin A and B, which sequester actin monomers and prevent polymerization, and Cytochalasins, which bind to the barbed end and inhibit subunit association and dissociation. The C2 toxin caps actin filaments, preventing further polymerization.
What are some examples of actin filament stabilizers, and how do they stabilize actin filaments
Actin filament stabilizers include Phallotoxins (such as Phalloidin) and Jasplakinolide, which bind to actin filaments between subunits and reduce the rate of dissociation, increasing the stability of the filament.
How do small, drug-like molecules, such as CK666 and SMIFH2, inhibit actin-binding proteins like Arp2/3 complex and formins, respectively
Small, drug-like molecules can inhibit actin-binding proteins, such as Arp2/3 complex and formins. CK666 inhibits actin filament branch formation by blocking the conformational change that activates Arp2/3 complex. SMIFH2 inhibits nucleation and elongation by many different formins.
what does Rho GTPases regulate
Rho GTPases are a family of small GTP-binding proteins that play a critical role in regulating the assembly of actin filaments.
what are microtubules, what are they composed of and what is there function
Microtubules are stiff cylindrical polymers composed of α-tubulin and β-tubulin, which provide structural support and serve as tracks for movement powered by kinesins and dyneins. They play a crucial role in organizing the cytoplasm during interphase and forming the mitotic spindle during cell division, which helps separate duplicated chromosomes.
what is dynamic instability
Dynamic instability is a phenomenon in which microtubules exhibit constant cycles of polymerization and depolymerization, resulting in the overall appearance of “dynamic instability.”
how are microtubules arranged cells
Tissue culture cells, microtubules (green) irradiate from the centrosome (red)
who discovered centrosomes
Edouard Van Beneden was a Belgian embryologist who first observed centrosomes and described them as “centrosphères”. Theodor Boveri, a German biologist, later named them centrosomes and conducted further research on their role in cell division
what does centrosomes consist of and what are they composed of
Centrosomes consist of a pair of centrioles, which are cylindrical structures composed of microtubules, and pericentriolar material.
what is the role of centrioles
Centrioles nucleate microtubules and are involved in organizing the microtubule cytoskeleton.
what type of organelles are cilia
Cilia are sensory organelles
what is called the basal body
The mother centriole at the base of a cilium is called the basal body
what does cilia maintain and how
cilia play critical roles in maintaining cell homeostasis by sensing and responding to the environment, facilitating the movement of fluids and particles, and mediating signaling pathways.
What is the difference in microtubule arrangement between the primary cilium and the motile cilium
The primary cilium has a 9+0 arrangement of microtubules, meaning there are nine microtubule doublets but no central pair, while the motile cilium has a 9+2 arrangement, with nine doublets and two central microtubules.
how does active transport occur in sensory cells with cilia
In sensory cells with cilia, active transport occurs through intraflagellar transport (IFT), a bidirectional process that moves cargo along microtubules within the cilium.
where are motile cilia present
Motile cilia are present in a variety of cells, including respiratory epithelia and sperm cells.
How do Vinblastine, Taxol, Colchicine, and nocodazole interfere with microtubule dynamics, and what is the clinical application of these drugs
- Tubulin binds several therapeutic compounds, including Vinblastine and Taxol, which are used in cancer chemotherapy by interfering with microtubule dynamics and blocking cell division.
- Vinblastine binds between tubulin dimers at the ends of microtubules, inhibiting mitosis.
- Taxol binds β-tubulin and stabilizes microtubules.
- Colchicine and nocodazole inhibit microtubule assembly by binding dissociated tubulin dimers. Colchicine stabilizes a bent conformation that cannot fit into the microtubule lattice.
- Colchicine is used empirically to treat gout, but its precise mechanism of action is not fully understood.
what are intermediate filaments, what is their function, and how big are they
Intermediate filaments are a type of cytoskeletal protein that provides mechanical support for animal cells. They are strong and flexible polymers composed of many different but homologous proteins. Intermediate filaments have a diameter of about 10 nm, which is intermediate between those of the thick and thin filaments in striated muscles.
what are 2 examples of intermediate filaments
There are several types of intermediate filaments, including lamins and keratins.
What is the main function of intermediate filaments in cells and tissues, and how does it differ from that of microfilaments and microtubules
Unlike microfilaments and microtubules, intermediate filaments do not play a direct role in cell motility or intracellular transport. Instead, they provide contractility, flexibility, and tensile strength to cells and tissues.
What are the typical colors used to label vimentin, microtubules, and actin in fluorescent images, and how do vimentin and keratin intermediate filaments differ in their behavior during mitosis?
In flourescent images, vimentin intermediate filaments would appear in red, microtubules in green, and actin (labeled with phalloidin) in blue. Vimentin intermediate filaments would typically be dispersed during mitosis, whereas keratin intermediate filaments would remain intact throughout mitosis.
where are keratins expressed and what can mutation in keratins affect
Keratins are expressed in stratified squamous epithelia and mutations in keratin genes can affect the integrity of the skin’s epithelium.
How do intermediate filaments complement the function of microtubules, actin filaments, and membranes in cells
Intermediate filaments are like flexible tendons within cells, preventing excessive stretching in response to internal or external forces. They interact with microtubules, actin filaments, and membranes to complement their function. Desmin filaments in smooth muscle, for example, transform into a continuous strap when the muscle is stretched.
what is the function of neurofilaments
In addition to providing mechanical stability, neurofilaments also play a role in increasing the diameter of the axon, which enhances the efficiency of electrical communication between neurons.
what are kinesins
Kinesins are motor proteins that move along microtubules in a specific direction, typically towards the plus end of the microtubule.
What is the role of ATPase domains in the movement of myosin, kinesin, and dynein along cytoskeletal fibers, and how has the evolution of these motor proteins contributed to the development of complex cellular structures and functions
Myosin, kinesin, and dynein all contain ATPase domains that hydrolyze ATP to provide the energy necessary for their movement along cytoskeletal fibers. These motor proteins have evolved from a common ancestor and have diverged to acquire specialized functions in different organisms and cell types. The evolution of these molecular motors has played a key role in the development of complex cellular structures and functions, such as muscle contraction, intracellular transport, and cell division.
how do motor proteins use ATP hydrolysis to generate force and produce motion in cells
The motors bind to a support or cargo and interact with cytoskeletal fibers like actin filaments or microtubules. The energy from ATP hydrolysis creates force that stretches an elastic element between the cargo and fiber, resulting in motion. The type of motion depends on whether the force in the spring is stronger than the resistance of the fiber or the cargo.
what is myosin
Myosin is a motor protein that moves along actin filaments, using them as tracks for movement.
how can vanadate and ultraviolet light inactive dyenein
Vanadate and ultraviolet light can both inactivate dynein, a molecular motor protein, but through different mechanisms.
Vanadate works by binding to the γ-phosphate site of dynein-adenosine diphosphate (ADP), inhibiting its function. However, vanadate also binds to other ATPases, making it nonspecific.
On the other hand, ultraviolet light can cleave and inactivate the dynein heavy chain, which is a component of the dynein motor complex. Monastrol is a kinesin-5 inhibitor that prevents the proper segregation of chromosomes during mitosis, while Blebbistatin blocks cytokinesis by inhibiting myosin-II in cytoplasmic and skeletal muscle. Higher-affinity inhibitors of kinesin-5 are being developed for cancer therapy.
what is intracellular motility
Intracellular motility refers to the movement of organelles, vesicles, and other cellular components within the cell.
what can mocrotubule transport
microtubule motors can attach to membranes and transport vesicles and other cargo along the cytoskeleton.
what is axonal transport and what are the 2 types of axonal transport
Axonal transport is the process by which various cargoes, such as mitochondria, lipids, synaptic vesicles, and proteins, are transported along the cytoskeleton of an axon, which is a long, thin extension of a neuron.
There are two types of axonal transport: anterograde transport, which moves cargoes from the cell body towards the axon terminals, and retrograde transport, which moves cargoes from the axon terminals towards the cell body. The process is mediated by microtubule-based molecular motors.
how can cytoskeletal polymers alter the shape of the cell
The cytoskeleton provides mechanical support to cells and also contributes to cellular shape and movement. Assembly of new cytoskeletal polymers or rearrangement of preexisting ones can alter the shape of the cell.
what are 2 examples of cell shapes changes produced by contraction
Muscle contraction and cytokinesis are examples of cell shape changes produced by contraction.
what are pseudopod extension
Pseudopod extension is a form of locomotion
what affects cell motility
Substrate can affect cellular motility
What experimental approach can be used to study actin filament dynamics at the leading edge of cell migration
Studying actin filament dynamics at the leading edge of cell migration can be done using photobleaching experiments, which show that actin assembles at the leading edge.
What are some examples of cells that exhibit chemotaxis, and what are the chemical cues that they are attracted to
Chemotaxis is observed in Dictyostelium and leukocytes during infection. Dictyostelium shows chemotaxis towards cyclic adenosine monophosphate (cAMP), while leukocytes are attracted to chemokines and bacterial metabolites at infection sites.
What is growth cone guidance and how does it regulate cell motility during development
Growth cone guidance is a model for regulating cell motility during development. It involves extension and growth of neuronal processes, as well as chemical cues that guide transport of organelles and other elements inside the cell.
What is the role of focal adhesions in cell motility
Focal adhesions are reversible connections between the extracellular matrix and the cytoskeleton in moving cells.
What is the role of focal adhesions in cell motility and what structures do they connect in the cell
Focal adhesions are protein complexes that link the extracellular matrix to the actin cytoskeleton and play a crucial role in cell motility. These structures are reversible and dynamic, constantly forming and disassembling as cells move and change shape.
What is cell movement and what does it involve
cell movement is a highly dynamic process that involves multiple cellular components and signaling pathways. Cells constantly adapt their shape and behavior in response to various extracellular and intracellular signals, allowing them to move and navigate through their environment.
What are muscles, and what are the three types of muscles found in the body
Muscles are contractile tissues that use actin and myosin to generate powerful, unidirectional movements. They are responsible for both visible and invisible movements such as walking, talking, breathing, and heartbeats, and can be regarded as the motors of the body. There are three types of muscles: skeletal, cardiac, and smooth. Muscle cells help keep us erect when we are still sitting or standing, and muscles comprise about 40% to 50% of body weight.
what are 4 functions of muscle in the body
Functions of Muscles:
- Producing movement: Muscles enable all kinds of voluntary movement and move the bones of the skeletal system through their connective tissue attachments.
- Maintaining posture and body position: When not moving, isometric muscle contractions hold various parts of the supportive skeletal system in position.
- Stabilizing joints: Muscles help stabilize joints by maintaining tension in the surrounding connective tissue.
- Maintaining body temperature: Muscle contraction generates heat that helps maintain body temperature.
what are 4 properties of muscles
Properties of Muscles:
- Excitability - responds to stimuli from motor or hormones
- Contractibility - can forcefully shorten
- Extensibility - can be stretched (lack of which is spasticity)
- Elasticity - can recoil to original length after being stretched
What are skeletal muscles, what is the main function of skeletal muscles and how are they controlled by the nervous system in terms of controlling their contraction
Skeletal muscles, also known as striped muscles or voluntary muscles, are attached to bones and responsible for the movement of the body in relation to the environment. They control the movement of hands, arms, legs, neck, trunk, and eyes. These muscles are multinucleate and their contraction is stimulated and controlled by the nervous system, making them voluntary. The nervous system sends signals to the muscles via nerves, which convert chemical energy into movement. Skeletal muscles attach to bone, skin, or fascia and can be voluntarily contracted and relaxed.
What are the unique features of cardiac muscle and how does it function to pump blood into the circulatory system
Cardiac muscle is the muscle tissue that makes up the bulk of the heart walls. It has a striated appearance and is involuntary, meaning it is not directly controlled by the nervous system. Cardiac muscle fibers are shorter than skeletal muscle fibers and usually contain only one nucleus. They are highly coordinated to pump blood into the circulatory system. Cardiac muscle fibers possess many mitochondria and myoglobin, producing ATP primarily through aerobic metabolism. The cardiac muscle cells are connected by intercalated discs that allow them to contract in a wave-like pattern, creating a pump. The heart is autorhythmic due to the built-in pacemaker in the cardiac muscle tissue.
What are pacemaker cells, where are they located in the heart, and how do they generate rhythmic contractions without input from the nervous system?
Pacemaker cells are specialized cells located in the sinoatrial node of the heart, responsible for initiating the rhythmic contractions of the heart. They are intrinsically excitable, meaning they can generate action potentials without input from the nervous system. The membrane potential of pacemaker cells spontaneously drifts toward threshold, causing action potentials to occur about once per second. These action potentials spread from cell to cell through gap junctions, activating all cells in the atrium within a few hundred milliseconds. After a brief delay in the atrioventricular node, the action potential and contraction spreads from cell to cell through the ventricle, resulting in the highly reproducible pattern of electrical activity that can be recorded on the surface of the body as an electrocardiogram.
what are cardiac myocytes and what is the significance of gap junctions in cardiac myocytes and how do they contribute to the coordinated contraction of the heart
Cardiac myocytes are short, branched muscle cells that are physically and electrically connected to each other via gap junctions. Gap junctions allow for the transmission of electrical activity between cells, enabling cardiac myocytes to act as a single functional unit or syncytium. This allows for the coordinated contraction of the heart and efficient pumping of blood.
How do cardiac myocytes enable the efficient pumping of blood and what is the role of gap junctions in this process
Gap junctions are specialized channels that allow the direct exchange of ions and small molecules between adjacent cells. This allows for the synchronization of cellular activities, such as the coordinated contraction of cardiac muscle cells.
how are gap junctions formed and what types of molecules can pass through gap junctions, and what types of molecules cannot
Gap junctions are formed by the alignment of connexin proteins in the plasma membrane of two adjacent cells, creating a channel that allows ions and small molecules to pass through. However, larger molecules such as proteins and nucleic acids cannot pass through these channels.
What is the structure and function of connexins in gap junctions, and how do they allow for the direct exchange of small molecules and ions between adjacent cells
Connexins are transmembrane proteins that form the subunits of gap junctions. Six connexin molecules come together to form a connexon, which is a cylindrical structure with a central pore. When two adjacent cells have connexons that align, they can form a gap junction channel between the two cytoplasms, allowing for the direct exchange of small molecules and ions.
where do specialized gap functions occur, and how does connexons allow precise control of electrical signalling between cells
Specialized gap junctions called electrical synapses occur on specific nerve cells and allow for rapid passage of ions between the two nerve cells. Individual connexons can be opened or closed, allowing for precise control of electrical signaling between the cells.
What is the structure of smooth muscle cells, and how does their contraction differ from that of skeletal muscle? Additionally, what are some examples of organs in which smooth muscle is found, and what bodily functions does it contribute to?
Smooth muscle cells are smaller than skeletal muscle cells, and they are spindle-shaped with one centrally located nucleus. Unlike skeletal muscle, smooth muscle lacks striations, which gives it a smooth appearance. Smooth muscle is involuntary, meaning that it is not under conscious control. The autonomic nervous system regulates the contractions of smooth muscle, but hormones and stretching can also affect its contraction. Smooth muscle is found in many internal organs, such as the bladder, uterus, stomach, intestines, and blood vessels. It is responsible for various bodily functions, such as pushing food through the digestive system and controlling the bladder and bowel. Smooth muscle can contract for a long period of time, making it well-suited for these types of functions.
