Cytoskeleton and cellular motility - Week 25

Question 1

what is the function of cytoskeletons

Answer 1

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.

Question 2

What are the roles of actin filaments in eukaryotic cells, including their contributions to plasma membrane organization and microvilli formation and function?

Answer 2

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.

Question 3

How do actin, microtubules, and intermediate filaments work together to support cellular functions, such as intracellular transport and cell division

Answer 3

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.

Question 4

where does actin filaments undergo rearrangements during cell migration

Answer 4

The Lamellipodium is the site where actin filaments undergo rearrangements during cell migration.

Question 5

what are the 2 ways that actin helps with cell movement

Answer 5

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.

Question 6

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

Answer 6

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.

Question 7

what does the process of actin polymerization use as the source of energy

Answer 7

The process of actin polymerization, in which actin monomers assemble into filaments, requires ATP (adenosine triphosphate) as an energy source.

Question 8

what does actin binding protein play a role in regulating

Answer 8

Actin binding proteins play a crucial role in regulating the assembly, disassembly, and organization of actin filaments in cells.

Question 9

what are some specific functions of different actin binding proteins

Answer 9

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.

Question 10

what are the different types of actin binding proteins with examples

Answer 10

• 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

Question 11

what is critical for lamellipodium

Answer 11

Actin is critical for the lamellipodium, the leading edge of a migrating cell.

Question 12

What are some examples of actin filament destabilizers, and how do they destabilize actin filaments

Answer 12

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.

Question 13

What are some examples of actin filament stabilizers, and how do they stabilize actin filaments

Answer 13

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.

Question 14

How do small, drug-like molecules, such as CK666 and SMIFH2, inhibit actin-binding proteins like Arp2/3 complex and formins, respectively

Answer 14

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.

Question 15

what does Rho GTPases regulate

Answer 15

Rho GTPases are a family of small GTP-binding proteins that play a critical role in regulating the assembly of actin filaments.

Question 16

what are microtubules, what are they composed of and what is there function

Answer 16

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.

Question 17

what is dynamic instability

Answer 17

Dynamic instability is a phenomenon in which microtubules exhibit constant cycles of polymerization and depolymerization, resulting in the overall appearance of “dynamic instability.”

Question 18

how are microtubules arranged cells

Answer 18

Tissue culture cells, microtubules (green) irradiate from the centrosome (red)

Question 19

who discovered centrosomes

Answer 19

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

Question 20

what does centrosomes consist of and what are they composed of

Answer 20

Centrosomes consist of a pair of centrioles, which are cylindrical structures composed of microtubules, and pericentriolar material.

Question 21

what is the role of centrioles

Answer 21

Centrioles nucleate microtubules and are involved in organizing the microtubule cytoskeleton.

Question 22

what type of organelles are cilia

Answer 22

Cilia are sensory organelles

Question 23

what is called the basal body

Answer 23

The mother centriole at the base of a cilium is called the basal body

Question 24

what does cilia maintain and how

Answer 24

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.

Question 25

What is the difference in microtubule arrangement between the primary cilium and the motile cilium

Answer 25

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.

Question 26

how does active transport occur in sensory cells with cilia

Answer 26

In sensory cells with cilia, active transport occurs through intraflagellar transport (IFT), a bidirectional process that moves cargo along microtubules within the cilium.

Question 27

where are motile cilia present

Answer 27

Motile cilia are present in a variety of cells, including respiratory epithelia and sperm cells.

Question 28

How do Vinblastine, Taxol, Colchicine, and nocodazole interfere with microtubule dynamics, and what is the clinical application of these drugs

Answer 28

• 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.

Question 29

what are intermediate filaments, what is their function, and how big are they

Answer 29

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.

Question 30

what are 2 examples of intermediate filaments

Answer 30

There are several types of intermediate filaments, including lamins and keratins.

Question 31

What is the main function of intermediate filaments in cells and tissues, and how does it differ from that of microfilaments and microtubules

Answer 31

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.

Question 32

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?

Answer 32

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.

Question 33

where are keratins expressed and what can mutation in keratins affect

Answer 33

Keratins are expressed in stratified squamous epithelia and mutations in keratin genes can affect the integrity of the skin’s epithelium.

Question 34

How do intermediate filaments complement the function of microtubules, actin filaments, and membranes in cells

Answer 34

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.

Question 35

what is the function of neurofilaments

Answer 35

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.

Question 36

what are kinesins

Answer 36

Kinesins are motor proteins that move along microtubules in a specific direction, typically towards the plus end of the microtubule.

Question 37

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

Answer 37

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.

Question 38

how do motor proteins use ATP hydrolysis to generate force and produce motion in cells

Answer 38

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.

Question 39

what is myosin

Answer 39

Myosin is a motor protein that moves along actin filaments, using them as tracks for movement.

Question 40

how can vanadate and ultraviolet light inactive dyenein

Answer 40

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.

Question 41

what is intracellular motility

Answer 41

Intracellular motility refers to the movement of organelles, vesicles, and other cellular components within the cell.

Question 42

what can mocrotubule transport

Answer 42

microtubule motors can attach to membranes and transport vesicles and other cargo along the cytoskeleton.

Question 43

what is axonal transport and what are the 2 types of axonal transport

Answer 43

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.

Question 44

how can cytoskeletal polymers alter the shape of the cell

Answer 44

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.

Question 45

what are 2 examples of cell shapes changes produced by contraction

Answer 45

Muscle contraction and cytokinesis are examples of cell shape changes produced by contraction.

Question 46

what are pseudopod extension

Answer 46

Pseudopod extension is a form of locomotion

Question 47

what affects cell motility

Answer 47

Substrate can affect cellular motility

Question 48

What experimental approach can be used to study actin filament dynamics at the leading edge of cell migration

Answer 48

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.

Question 49

What are some examples of cells that exhibit chemotaxis, and what are the chemical cues that they are attracted to

Answer 49

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.

Question 50

What is growth cone guidance and how does it regulate cell motility during development

Answer 50

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.

Question 51

What is the role of focal adhesions in cell motility

Answer 51

Focal adhesions are reversible connections between the extracellular matrix and the cytoskeleton in moving cells.

Question 52

What is the role of focal adhesions in cell motility and what structures do they connect in the cell

Answer 52

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.

Question 53

What is cell movement and what does it involve

Answer 53

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.

Question 54

What are muscles, and what are the three types of muscles found in the body

Answer 54

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.

Question 55

what are 4 functions of muscle in the body

Answer 55

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.

Question 56

what are 4 properties of muscles

Answer 56

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

Question 57

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

Answer 57

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.

Question 58

What are the unique features of cardiac muscle and how does it function to pump blood into the circulatory system

Answer 58

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.

Question 59

What are pacemaker cells, where are they located in the heart, and how do they generate rhythmic contractions without input from the nervous system?

Answer 59

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.

Question 60

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

Answer 60

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.

Question 61

How do cardiac myocytes enable the efficient pumping of blood and what is the role of gap junctions in this process

Answer 61

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.

Question 62

how are gap junctions formed and what types of molecules can pass through gap junctions, and what types of molecules cannot

Answer 62

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.

Question 63

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

Answer 63

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.

Question 64

where do specialized gap functions occur, and how does connexons allow precise control of electrical signalling between cells

Answer 64

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.

Question 65

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?

Answer 65

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.