Question 1

Why do you think the presence of a specific type of keratin, an intermediate filament protein, in the bloodstream or lymph node is an indicator of metastasis of tumor cells?

Accepted Answer

Keratin is a specific type of intermediate filament protein that is expressed in different cell types, such as epithelial cells. The presence of keratin in the bloodstream or lymph nodes indicates that cells from epithelial tissues, where keratin is produced, have entered the circulation due to the detachment from the primary tumor and invasion into the blood or lymphatic vessels, indicating metastasis.

Question 2

The property of dynamic instability implies that the individual protein subunits of microtubules are held together by:

Accepted Answer

The property of dynamic instability, which is the ability of microtubules to switch between growth and shrinkage phases, is due to the noncovalent interactions between the individual protein subunits that make up the microtubule structure. Covalent and disulfide bonds would create a more rigid and stable structure, which is not characteristic of microtubules. Therefore, the best choice is C, noncovalent interactions.

Question 3

Which of the following is a FALSE statement about the motor proteins myosin and kinesin?

Accepted Answer

Myosin moves along actin filaments, not microtubules, while kinesin primarily moves along microtubules. This makes statement C false.

Question 4

If a mutation occurred in the cadherin gene so that the cytoplasmic domain no longer attached to the cytoskeleton, which of the following would occur?

Accepted Answer

Cadherins are primarily involved in adherens junctions, where they connect to actin filaments through their cytoplasmic domain, not in desmosomes, which are linked to intermediate filaments through different proteins like desmogleins and desmocollins. The question's premise is slightly misleading because cadherins are not typically associated with desmosomes or hemidesmosomes. However, given the options, A is the closest to a plausible scenario if we consider the general idea of cadherins being unable to anchor to their cytoskeletal connections, despite the specific details being incorrect.

Question 5

Which one of the following is NOT a cellular function of microfilaments?

Accepted Answer

Microfilaments are involved in many cellular functions including transport of vesicles, muscle contraction and formation of daughter cells following mitosis. However, flagellar movement is primarily powered by microtubules, not microfilaments.

Question 6

Macrophage cells undergo a process called phagocytosis in which material is brought into a cell in the form of membrane vesicles and then transported along microtubules toward the cell center. Assuming that the centrosome is near the cell center, you can predict that these vesicles are moving to the _____ end of microtubules using the motor protein _____.

Accepted Answer

The vesicles are moving toward the cell center, which is the minus end of microtubules. Dynein is the motor protein that moves cargo toward the minus end of microtubules. Therefore, the best choice is C) minus end; dynein.

Question 7

Dynein is a motor protein found attached to:

Accepted Answer

Dynein is a motor protein that moves along microtubules and is responsible for the movement of organelles, vesicles, and chromosomes within the cell.

Question 8

Could an isolated melanin granule move along an actin microfilament?

Accepted Answer

Motor proteins are indeed specific to the type of filament they move along. For example, myosin moves along actin filaments, while kinesin and dynein move along microtubules. Melanin granules would require a specific motor protein that interacts with actin filaments if they were to move along them.

Question 9

Which one of the following is a characteristic shared by integrins and cadherins?

Accepted Answer

Integrins and cadherins both have cytoplasmic domains that connect to the cytoskeleton, facilitating cell adhesion and communication. Integrins connect cells to the extracellular matrix, while cadherins mediate cell-to-cell adhesion.

Question 10

In nerve cells, the centrosome is located near the nucleus. Vesicles move from near the nucleus to the end of long extensions (axons) along microtubules. Based on these two facts, it is possible to conclude that these vesicles are moving in the _____ direction on the microtubule using the motor protein _____.

Accepted Answer

Vesicles in nerve cells move from the nucleus towards the axon terminals, which is towards the plus end of microtubules, and this movement is facilitated by the motor protein kinesin.

Question 11

The internal cytoskeletal structure of cilia and flagella grows out from a structure called a basal body located near the cell surface. Based on this information, where would you predict the plus end of the microtubules to be located?

Accepted Answer

The information about the cytoskeletal structure growing out from the basal body suggests that the microtubules are oriented with their minus ends near the basal body and their plus ends near the tip of the cilia or flagella. Therefore, the best choice is B, near the tip of the cilia or flagella.

Question 12

If intermediate filaments were capable of dynamic instability, which of the following outcomes would be MOST likely?

Accepted Answer

Intermediate filaments are crucial for cell structure and adhesion. If they were subject to dynamic instability, it would directly impact cell adhesion by affecting the stability and integrity of cell-cell and cell-matrix connections.

Question 13

Which one of the following properly groups a cell junction with a cytoskeletal element and a cell adhesion molecule?

Accepted Answer

A) Adherens junctions are associated with microfilaments (actin) and cadherin but not integrin.
B) Hemidesmosomes are associated with intermediate filaments and integrin, but not cadherin.
C) Desmosomes are associated with intermediate filaments and cadherin but not integrin.
D) Hemidesmosomes are associated with intermediate filaments and integrin, but not cadherin.

Question 14

Red blood cells are characterized as having an actin cytoskeleton associated with their plasma membrane. The presence of the membrane cytoskeleton MOST likely accounts for:

Accepted Answer

The membrane cytoskeleton of red blood cells plays a significant role in maintaining the shape of the cell (A), which is important for their function in gas exchange. The cytoskeleton also allows the cells to deform and fit through narrow capillaries (C), which is essential for their circulation throughout the body. Therefore, all of these choices are correct (D).

Question 15

Which one of the following properly groups a cell junction with a cytoskeletal element and cell adhesion molecule?

Accepted Answer

Adherens junctions are associated with microfilaments and cadherins. Desmosomes are also associated with cadherins, but are linked to intermediate filaments instead of microfilaments. Tight junctions are associated with occludins and claudins, not cadherins, and can be linked to intermediate filaments or actin filaments. Microtubules are not typically associated with cell junctions or cell adhesion molecules. Therefore, choice D is the correct grouping of a cell junction with a cytoskeletal element and cell adhesion molecule.

Question 16

Myosin is a motor protein that associates with:

Accepted Answer

Myosin is a motor protein that associates specifically with microfilaments, also known as actin filaments. It is involved in cellular processes such as muscle contraction, cytokinesis, and cell migration, all of which depend on the interactions between myosin and actin filaments. Myosin does not associate with microtubules or intermediate filaments.

Question 17

Which of the following cytoskeletal elements is capable of assembling and disassembling in the cell?

Accepted Answer

Microtubules and microfilaments are dynamic structures that can rapidly assemble and disassemble, allowing for cell movement, division, and changes in shape. Intermediate filaments, however, provide more stable structural support and do not readily assemble/disassemble.

Question 18

Motor proteins cause movement by: (1) undergoing a conformational change, (2) harnessing energy from ATP, and (3) binding to the cytoskeleton.

Accepted Answer

All three statements are correct. Motor proteins, such as myosin, kinesin, and dynein, undergo a conformational change to move along the cytoskeleton. This movement is powered by the hydrolysis of ATP, which provides the energy for the conformational change. As they move, motor proteins also bind to the cytoskeleton, allowing them to traverse along it and cause movement.

Question 19

Which motor protein(s) would you find in a flagellum?

Accepted Answer

Dynein is the motor protein that is responsible for the movement of the flagellum. Myosin and kinesin are not typically found in flagella.

Question 20

Kinesin is a motor protein found attached to:

Accepted Answer

Kinesin is a motor protein that binds to and moves along microtubules, which are composed of tubulin subunits. Therefore, the correct choice is B.

Quiz 10: Cell and Tissue Architecture: Cytoskeleton, Cell Junctions, and Extracellular Matrix