Molecular Cell Biology - Problem Drill 20: Cytoskeleton and Cellular Mobility

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1 Molecular Cell Biology - Problem Drill 20: Cytoskeleton and Cellular Mobility Question No. 1 of Which of the following statements about cytoskeletal filaments is correct? Question #1 (A) The Cytoskeleton is made up of 2 types of protein filaments: (A) Actin filaments and (B) Microtubules. (B) The Cytoskeleton is made up of 3 types of protein filaments: (A) Actin filaments, (B) Microtubules and (C) Intermediate Filaments. (C) Cellular filaments are assembled into 2 different sizes: (A) Actin filaments are the smallest (7nm), and (B) Microtubules are the largest (25nm). (D) Cellular filaments are assembled into 2 different sizes: (A) Microtubules are the smallest (7nm), and (B) Actin filaments are the largest (25nm). The Cytoskeleton is made up of 3 types of protein filaments: (A) Actin filaments, (B) Microtubules and (C) Intermediate Filaments. B. Correct! The Cytoskeleton is made up of 3 types of protein filaments: (A) Actin filaments, (B) Microtubules and (C) Intermediate Filaments. Cellular filaments are assembled into 3 different sizes: (A) Actin filaments are the smallest (7nm), (B) Intermediate filaments are in the middle (10nm) and (C) Microtubules are the largest (25nm). Cellular filaments are assembled into 3 different sizes: (A) Actin filaments are the smallest (7nm), (B) Intermediate filaments are in the middle (10nm) and (C) Microtubules are the largest (25nm). The Cytoskeleton is both rigid enough to support the shape of the cell and flexible enough to be reorganized frequently. The Cytoskeleton is made up of 3 types of protein filaments: (A) Actin filaments, (B) Microtubules and (C) Intermediate Filaments. Each type of filament is formed through the assembly of different protein subunit. Cellular filaments are assembled into 3 different sizes: (A) Actin filaments are the smallest (7nm), (B) Intermediate filaments are in the middle (10nm) and (C) Microtubules are the largest (25nm).

2 Question No. 2 of Actin filaments. Question #2 (A) Are also known as large filaments, and are organized into bundles just underneath the plasma membrane. (B) Exist as single fibers in cells with actin-binding proteins, such as myosin. (C) Bundles are cross-linked into a network with actin-binding proteins, such as myosin. (D) In cross-linked bundles have no influence the shape and movement of the plasma membrane. Actin filaments, also known as microfilaments, are organized into bundles just underneath the plasma membrane. Actin filament bundles are cross-linked into a network with actin-binding proteins, such as myosin. C. Correct! Actin filament bundles are cross-linked into a network with actin-binding proteins, such as myosin. Cross-linked actin bundles directly influence the shape and movement of the plasma membrane and facilitate such things as T-cell migration. Actin filaments, also known as microfilaments, are organized into bundles just underneath the plasma membrane. Actin filaments, along with motor proteins such as myosin, are reorganized as cells change their shape and move. Actin filament bundles are cross-linked into a network with actin-binding proteins, such as myosin. These bundles directly influence the shape and movement of the plasma membrane and facilitate such things as T-cell migration.

3 Question No. 3 of Which of the following statements about intermediate filaments is correct? Question #3 (A) Intermediate filaments are made up of various intermediate filament proteins including: keratins, vimentin, neurofilament proteins and nuclear lamins. (B) Intermediate filaments are made up of various intermediate filament proteins including: keratins, vimentin, myosin and actin. (C) They all share the lattice-type cross-linked structure and are prominent around the nucleus and extend out towards the periphery of the cell. (D) They all share the lattice-type cross-linked structure and are prominent inside the nucleus and extend out towards the periphery of the cell. A. Correct! Intermediate filaments are made up of various intermediate filament proteins including: keratins, vimentin, neurofilament proteins and nuclear lamins. Intermediate filaments are made up of various intermediate filament proteins including: keratins, vimentin, neurofilament proteins and nuclear lamins. They all share the same long rope-like structure and are prominent around the nucleus and extend out towards the periphery of the cell. They all share the same long rope-like structure and are prominent around the nucleus and extend out towards the periphery of the cell. Intermediate filaments are made up of various intermediate filament proteins including: keratins, vimentin, neurofilament proteins and nuclear lamins. They all share the same long rope-like structure and are prominent around the nucleus and extend out towards the periphery of the cell. Intermediate filaments provide the cell with strength and carry mechanical stress. They are present in large numbers in epithelial cells and are linked from cell to cell. They also lie along the length of axons, providing strength as it spans over great distances in the body.

4 Question No. 4 of Which of the following statements about microtubules is correct? Question #4 (A) Microtubules are long, hollow tube-like cylinders, which are made up of the protein tubulin. (B) Microtubules are long, hollow tube-like cylinders, which are made up of the protein actin. (C) They are the smallest and weakest component of the cytoskeleton. (D) Microtubules are involved in calcium ion movement within cells. A. Correct! When the receptor changes its conformation the associated G-protein to bind GTP and go on to activate or inactivate a plasma membrane associated protein. Microtubules are long, hollow tube-like cylinders, which are made up of the protein tubulin. They are the largest and strongest component of the cytoskeleton. Microtubules also are involved in vesicle and organelle movement within cells. Microtubules are long, hollow tube-like cylinders, which are made up of the protein tubulin. They are the largest and strongest component of the cytoskeleton. Microtubules are usually organized into vast arrays in cells with 1 end attached to a single microtubule organizing center called a centrosome. Microtubules help polarize and shape cells when stabilized by associated proteins. Microtubules also are involved in vesicle and organelle movement within cells. This is possible with 2 microtubule-dependent motor proteins called dyneins and kinesins.

5 Question No. 5 of Which of the following statements about cytoskeleton filament self assembly is correct? Question #5 (A) The process ends with nucleation, where filament subunits are assembled into trimer groups; they are then stable enough to combine with other trimer groups and, together, begin to form an elongated fiber. (B) When an actin or tubulin subunit is incorporated into the growing filament, the bound ADP (actin) or GDP (tubulin) is hydrolyzed. (C) Cytoskeleton filament self assembly is a dynamic process which involves the formation of stable subunits that allow the filament to form and elongate. (D) Cytoskeleton filament self assembly is a rigid process which involves the formation of irreversible subunits that allow the filament to form and elongate. The process begins with nucleation, where filament subunits are assembled into trimer groups; they are then stable enough to combine with other trimer groups and, together, begin to form an elongated fiber. When an actin or tubulin subunit is incorporated into the growing filament, the bound ATP (actin) or GTP (tubulin) is hydrolyzed. C. Correct! Cytoskeleton filament self assembly is a dynamic process which involves the formation of stable subunits that allow the filament to form and elongate. Cytoskeleton filament self assembly is a dynamic process which involves the formation of stable subunits that allow the filament to form and elongate. Cytoskeleton filament self assembly is a dynamic process which involves the formation of stable subunits that allow the filament to form and elongate. The assembly of filaments is a balance between the addition of subunits at one end and the disassembly at the other end of the filament. The process begins with nucleation, where filament subunits are assembled into trimer groups; they are then stable enough to combine with other trimer groups and, together, begin to form an elongated fiber. Elongation occurs as subunits are added to either end of the growing filament, until a steady state is reached where the addition of subunits is matched with the disassembly of subunits. This general process occurs for both actin filaments and microtubules.

6 Question No. 6 of Which of the following statements about cellular regulation of microtubule filaments is correct? Question #6 (A) γ-tubulin is a unique form of tubulin protein that binds actin subunits and forms a γ-actin ring complex along with other associated proteins. (B) MTOC is where the microtubules end they are nucleated in the cell periphery. (C) The formation of microtubules is regulated by a number of factors: (A) γ- tubulin, (B) Microtubule-organizing center (MTOC) and (C) microtubuleassociated proteins. (D) The formation of microtubules is regulated by a number of factors: (A) γ- tubulin, (B) Microtubule-organizing center (MTOC) and (C) receptor tyrosine kinases. γ-tubulin is a unique form of tubulin protein that binds tubulin subunits and forms a γ-tubulin ring complex along with other associated proteins. MTOC is where the microtubules are nucleated and then spread out in an array towards the cell periphery. C. Correct! The formation of microtubules is regulated by a number of factors: (A) γ-tubulin, (B) Microtubule-organizing center (MTOC) and (C) microtubule-associated proteins. The formation of microtubules is regulated by a number of factors: (A) γ-tubulin, (B) Microtubule-organizing center (MTOC) and (C) microtubule-associated proteins. The formation of microtubules is regulated by a number of factors: (A) γ-tubulin, (B) Microtubule-organizing center (MTOC) and (C) microtubule-associated proteins. γ-tubulin is a unique form of tubulin protein that binds tubulin subunits and forms a γ-tubulin ring complex along with other associated proteins. This ring serves as a template from which a microtubule nucleates. MTOC is where the microtubules are nucleated and then spread out in an array towards the cell periphery. This array surveys the outlying regions of the cell and helps regulate filament length and number.

7 Question No. 7 of Which of the following statements about the cellular regulation of actin filaments is correct? Question #7 (A) Cells have a single mechanism to regulate the formation of actin filaments: actin-related proteins (ARPs). (B) Cells have various mechanisms to regulate the formation of actin filaments: (A) Actin-related proteins (ARPs), (B) protein binding to free subunits and (C) actin-severing proteins. (C) Profilin is an example of a protein that prevents the binding of free actin subunits. (D) Actin-severing proteins, such as profilin, bind to actin filaments and ultimately severe them into smaller units. Cells have various mechanisms to regulate the formation of actin filaments: (A) Actin-related proteins (ARPs), (B) protein binding to free subunits and (C) actinsevering proteins. B. Correct! Cells have various mechanisms to regulate the formation of actin filaments: (A) Actin-related proteins (ARPs), (B) protein binding to free subunits and (C) actinsevering proteins. Profilin is an example of a protein that binds to free actin subunits. Actin-severing proteins, such as gelsolin, bind to actin filaments and ultimately severe them into smaller units. Cells have various mechanisms to regulate the formation of actin filaments: (A) Actin-related proteins (ARPs), (B) protein binding to free subunits and (C) actinsevering proteins. Actin-related proteins such as ARP2/3, provide a nucleation site for the actin filament. This usually takes place near the plasma membrane and it, in turn, is subject to regulation by external signals. Profilin is an example of a protein that binds to free actin subunits. Upon binding, profilin increases the insertion of the subunit into the growing actin filament. Profilin is then released and can bind to additional free subunits. Actin-severing proteins, such as gelsolin, bind to actin filaments and ultimately severe them into smaller units. Initially, gelsolin binds to the actin filament then it inserts itself between 2 actin subunits; after it has severed the actin filament, it remains bound and caps the free end.

8 Question No. 8 of Which of the following statements about molecular motors is correct? Question #8 (A) Molecular motors (motor proteins) bind to cytoskeletal filaments and hydrolyze ATP to provide the necessary energy to move along it. (B) Molecular motors (motor proteins) bind to the plasma membrane and hydrolyze ADP to provide the necessary energy to move along it. (C) Molecular motors hydrolyze ADP and undergo a conformational change. (D) They release the filament and undergo conformational relaxation, and then do not re-bind to filaments. A new motor protein is required to bind to the filament and move forward by 1 step (typically a few nanometers). A. Correct! Molecular motors (motor proteins) bind to cytoskeletal filaments and hydrolyze ATP to provide the necessary energy to move along it. Molecular motors (motor proteins) bind to cytoskeletal filaments and hydrolyze ATP to provide the necessary energy to move along it. Molecular motors hydrolyze ATP and undergo a conformational change. They release the filament and undergo conformational relaxation, and can then bind to filaments and the motor protein and cargo, or the filament itself moves forward by 1 step (typically a few nanometers). Molecular motors (motor proteins) bind to cytoskeletal filaments and hydrolyze ATP to provide the necessary energy to move along it. There are over 10 different types of motor proteins in cells, and they differ in the type of cytoskeletal filament they bind to and the direction in which they move. Motor proteins are involved in the movement of vesicles and organelles within cells, as well as movement of the cell itself. Molecular motors utilize the energy released from the hydrolysis of ATP to facilitate their function. Motor proteins create movement in cells using the following general principles: (A) Bind to filaments at their head region or motor domain. (B) Hydrolyze ATP and undergo a conformational change. (C) Release the filament and undergo conformational relaxation. (D) Bind to filaments and the motor protein and cargo, or the filament itself moves forward by 1 step (typically a few nanometers).

9 Question No. 9 of Which of the following statements about protrusion, during cellular locomotion is correct? Question #9 (A) Protrusion is the first step in the process of cell motility. (B) Lamin polymerization provides the force that pushes the plasma membrane outward, forming protrusive processes such as Lamellipodia and Filopodia. (C) Nucleation occurs near the nucleus and, consequently, the growing filaments push out on the nuclear membrane. (D) Protrusion is the middle step in the process of cell motility. A. Correct! Protrusion is the first step in the process of cell motility. Actin polymerization provides the force that pushes the plasma membrane outward, forming protrusive processes such as Lamellipodia and Filopodia. Nucleation occurs at the plasma membrane and, consequently, the growing filaments push out on the plasma membrane and the disassembly of the filament takes place deeper in the cell. Protrusion is the first step in the process of cell motility. Cell locomotion can be divided into 3 phases: (A) Protrusion, (B) Attachment and (C) traction. Protrusion is the first step in the process of cell motility. Actin polymerization provides the force that pushes the plasma membrane outward, forming protrusive processes such as Lamellipodia and Filopodia. Within the Lamellipodia and Filopodia, are growing actin filaments and motor proteins that move the protrusion forward. Nucleation occurs at the plasma membrane and, consequently, the growing filaments push out on the plasma membrane and the disassembly of the filament takes place deeper in the cell.

10 Question No. 10 of Which of the following statements about the actin-dependant phases of cellular locomotion is correct? Question #10 (A) Cell locomotion can be divided into 2 phases: (A) Protrusion and (B) traction. (B) Cell locomotion can be divided into 3 phases: (A) Protrusion, (B) Attachment and (C) traction. (C) During the attachment process of cell locomotion, the protruding organelles bind to the substratum. (D) After the cell has made new focal contact points, there is no detachment from focal contact near the back of the cell and contraction of the cell cytoskeleton. Cell locomotion can be divided into 3 phases: (A) Protrusion, (B) Attachment and (C) traction. B. Correct! Cell locomotion can be divided into 3 phases: (A) Protrusion, (B) Attachment and (C) traction. During the attachment process of cell motility, the protruding Lamellipodia and Filopodia bind to the substratum. After the cell has made new focal contact points, there is detachment from focal contact near the back of the cell and contraction of the cell cytoskeleton. Cell locomotion can be divided into 3 phases: (A) Protrusion, (B) Attachment and (C) traction. Protrusion is the first step in the process of cell motility. Actin polymerization provides the force that pushes the plasma membrane outward, forming protrusive processes such as Lamellipodia and Filopodia. Within the Lamellipodia and Filopodia, are growing actin filaments and motor proteins that move the protrusion forward. Nucleation occurs at the plasma membrane and, consequently, the growing filaments push out on the plasma membrane and the disassembly of the filament takes place deeper in the cell. During the attachment process of cell motility, the protruding Lamellipodia and Filopodia bind to the substratum. This provides many anchorage points for the cell as it moves. Actin filaments are attached to the substratum by focal contacts. These focal contact points usually occur near the advancing front of the cell. After the cell has made new focal contact points, there is detachment from focal contact near the back of the cell and contraction of the cell cytoskeleton. The extension of the plasma membrane forward, as well as contraction of the rear portion of the cell leads to the forward motility of the cell.