Question 1

Fibrous structural proteins of the extracellular matrix are embedded in gels formed from polysaccharides called

Accepted Answer

Fibrous structural proteins like collagen and elastin are embedded in polysaccharide gels called glycosaminoglycans (GAGs), which provide hydration and support to the matrix. Fibronectin and laminin are other structural proteins found in the extracellular matrix, but they do not form the gels in which the fibrous proteins are embedded.

Question 2

The major function of adhesion proteins such as fibronectin is to

Accepted Answer

Adhesion proteins such as fibronectin link collagen, proteoglycans, and cells containing integrins. This helps to maintain a stable extracellular environment by anchoring cells in place and facilitating communication between them. Additionally, adhesion proteins may also play a role in tissue development and wound healing.

Question 3

Integrins link extracellular matrix proteins, either directly or indirectly, to all of the following intracellular proteins except

Accepted Answer

Integrins can directly or indirectly link extracellular matrix proteins to actin, talin, and F1F1F1S1F1F1F10-actinin, but not to laminin. Laminin is a component of the extracellular matrix and cannot be linked to intracellular proteins.

Question 4

Which statement about integrins is false?

Accepted Answer

The correct subunit sequence is F1F1F1S1αF1F1F10 and F1F1F1S1βF1F1F1S1βF1F1F10. The subunit sequence mentioned in statement A is not correct.

Question 5

The cell-cell interactions mediated by the selectins, integrins, and most members of the Ig superfamily are _______ interactions in which the cytoskeletons of adjacent cells are not linked to one another.

Accepted Answer

The question specifically mentions selectins, integrins, and most members of the Ig superfamily, which are all known to mediate transient interactions between cells. Additionally, the statement that the cytoskeletons of adjacent cells are not linked to one another further supports the idea that these interactions are transient rather than stable. Therefore, the best choice is D: transient.

Question 6

Homophilic interactions between cells involve interactions

Accepted Answer

Homophilic interactions involve interactions among adhesion molecules of the same molecular class.

Question 7

Adherens junctions and desmosomes may be distinguished from each other on the basis of

Accepted Answer

Adherens junctions link cadherins to actin filaments, while desmosomes link cadherins to intermediate filaments.

Question 8

Specific recognition between cell types such as leukocytes and endothelial cells of blood vessels is mediated by cell-surface glycoproteins called

Accepted Answer

The specific recognition between cell types such as leukocytes and endothelial cells of blood vessels is mediated by cell-surface glycoproteins called selectins. Fibronectins, spectrins, and porins are not involved in this process.

Question 9

A major function of tight junctions is to

Accepted Answer

Tight junctions are specialized structures that seal the space between adjacent cells, forming a barrier that regulates the movement of ions and molecules across epithelial tissues. This function is important in maintaining the polarity of the cell membrane and in preventing the uncontrolled diffusion of substances across the barrier. Tight junctions also help to prevent the loss of extracellular fluid from tissues and serve as a structural support for epithelial cells.

Question 10

The junctions between animal cells that allow the free passage of molecules smaller than approximately 1000 daltons are called

Accepted Answer

Gap junctions are specialized intercellular connections between animal cells that allow for the unrestricted passage of small molecules and ions directly between the cytoplasm of adjacent cells. These junctions are made up of channels called connexons, which are formed by proteins called connexins. Tight junctions, on the other hand, seal the gap between adjacent animal cells to prevent the leakage of molecules between them, while plasmodesmata are junctions that allow for the movement of substances between plant cells. Hemidesmosomes anchor epithelial cells to the basal lamina.

Question 11

Although structurally different from gap junctions in animal cell tissues, _______ may be thought of as the functional equivalent of gap junctions in plants.

Accepted Answer

Plasmodesmata are channels that connect adjacent plant cells, allowing for the exchange of water, nutrients, and other signaling molecules. They are similar in function to gap junctions in animal tissues. Adherens junctions, desmosomes, and hemidesmosomes are all types of junctions found in animal tissues, but they serve different structural and functional roles than gap junctions.

Question 12

Suppose that a research group is conducting experiments to test how penicillin kills bacteria. Their starting point is a recent finding that penicillin inhibits the enzyme cross-linked between different strands of the peptidoglycan that forms the principal component of the bacterial cell wall. Formulate a hypothesis based on an analogy between the bacterial and plant cell wall and on the concept of turgor pressure. Briefly state the hypothesis, and propose an experiment to test it.

Accepted Answer

The answer of Suppose that a research group is conducting...

Question 13

Suppose you have treated plant cells in culture with a drug to disrupt microtubules. You then examine the orientation of cellulose fibrils in newly-synthesized primary cell walls that developed under these conditions. What will be the observed orientation of the cellulose fibrils with respect to one another?

Accepted Answer

The answer of Suppose you have treated plant cells in...

Question 14

How is proline hydroxylation in collagen encoded in the genome? What is the relationship between this encoding mechanism and scurvy?

Accepted Answer

The answer of How is proline hydroxylation in collagen encoded...

Question 15

Unlike polysaccharides such as glycogen or cellulose, glycosaminoglycans (GAGs) are highly negatively charged. What is the source and function of this negative charge?

Accepted Answer

The answer of Unlike polysaccharides such as glycogen or cellulose,...

Question 16

Hemidesmosomes link intermediate filaments inside intestinal epithelial cells to the basal lamina, an organized zone of extracellular matrix that underlies the intestinal epithelium. What is the advantage of this to a flexible tissue?

Accepted Answer

The answer of Hemidesmosomes link intermediate filaments inside intestinal epithelial...

Question 17

Integrins are dimeric transmembrane proteins of the plasma membrane. According to the fluid mosaic model of membrane structure (see Chapter 14), transmembrane proteins should be free to diffuse within the lipid bilayer. Yet, as shown by Tamkun and colleagues in 1986, integrins have a very restricted distribution in the plasma membrane of fibroblasts. The distribution often appears as a series of tracks across the cell surface. How can this distribution be explained?

Accepted Answer

The answer of Integrins are dimeric transmembrane proteins of the...

Question 18

A standard approach to detaching tissue culture cells from substratum is to incubate the culture briefly in a saline solution containing a divalent cation chelator and trypsin. How does this procedure detach the cells from the surface?

Accepted Answer

The answer of A standard approach to detaching tissue culture...

Question 19

In vivo, epithelial cells exhibit basolateral and apical surfaces. The tight junctional complex separates these two distinct cell surfaces from each other and joins the cells into an epithelial cell layer. In vivo cells showing such properties are resistant to ion flow across the cell layer. In vitro, many cultured epithelial cell systems show high electrical resistance but fail to exhibit a polarized distribution of proteins and lipids between the apical and basolateral surfaces. Present a working hypothesis to explain this observation.

Accepted Answer

The answer of In vivo, epithelial cells exhibit basolateral and...

Question 20

The X-linked variant of Charcot-Marie-Tooth disease is likely caused by mutations in a gene encoding a probable connexin 32. Suppose your laboratory is working with a human cell line called HeLa cells, which do not express connexins. Propose an experiment to demonstrate that the probable wild-type connexin 32 is actually a gap junction protein.

Accepted Answer

The answer of The X-linked variant of Charcot-Marie-Tooth disease is...

Quiz 16: Cell Walls, the Extracellular Matrix, and Cell Interactions