GRE Subject Test: Biology : Understanding Cell Junctions

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Cell Junctions

__________ are specialized cell junctions that connect the cytoplasm of two cells and allow for the exchange of various ions and molecules.

Possible Answers:

Tight junctions

Gap junctions

Adherens junctions

Desmosomes 

Correct answer:

Gap junctions

Explanation:

As the name implies, gap junctions are literally a gap in the plasma membranes of two adjacent cells that connect their cytoplasms. These junctions allow for electrical synapses and rapid cell signaling. While most notably present in cardiac muscle, gap junctions are also present in some neural cells and receptors.

Adherens junctions anchor cells through interactions with the actin cytoskeleton. Desmosomes use cadherin proteins to anchor cells via interactions with intermediate filaments. Tight junctions are used to create barriers that selectively allow molecules through layers of epithelial cells. 

Example Question #2 : Understanding Cell Junctions

Which of the following is true about cell junctions?

Possible Answers:

Certain junctions are capable of connecting the cytoplasm of two adjacent cells to allow for the free exchange of ions and small molecules

Certain junctions can create barriers that are nearly impermeable to fluid flow

All of these are true of cell junctions

Certain types of junctions can anchor neighboring cells to one another via their cytoskeletons

Correct answer:

All of these are true of cell junctions

Explanation:

All of the choices describe functions of different types of cell junctions. Anchoring junctions (such as adherens junctions and desmosomes) use the cytoskeletons of each cell, as well as certain transmembrane proteins, to anchor the cells together. Gap junctions create gaps in the plasma membrane between two adjacent cells that connect their cytoplasms. Tight junctions are capable of forming barriers that are nearly impermeable to fluid flow. 

Example Question #1 : Understanding Cell Junctions

Which cellular junction is most important in spreading action potentials throughout cardiac muscle?

Possible Answers:

Gap junctions

Desmosomes

Tight junctions

Valves

Correct answer:

Gap junctions

Explanation:

In order to have the action potential spread evenly and completely throughout the cardiac muscle cells, the cells need junctions that allow for ions to move between them. This action is accomplished by gap junctions between the cells. The intercalated discs between cardiac muscle cells are composed of gap junctions, and allow for electrical stimulation to travel from one cell to the next. This feature means that cardiac muscle can be depolarized and contract simultaneously.

Tight junctions are used to prevent fluid flow between cells. Desmosomes help with force transduction by linking the cytoskeletons of adjacent cells. Valves are not a type of cellular junction, and are macrostructures that prevent the backflow of fluids in vessels of the body.

Example Question #4 : Understanding Cell Junctions

Which cellular junction acts as a barrier to prevent fluids from passing between cells?

Possible Answers:

Villi

Gap junctions

Tight junctions

Desmosomes

Correct answer:

Tight junctions

Explanation:

Cellular junctions allow cells to block materials from moving between cells, or for providing communication between cells. Tight junctions are junctions between cells that form a tight seal. This prevents water and other fluids from moving past the cells. Tight junctions are essential for maintaining concentration gradients, preventing osmosis from equilibrating ion concentrations between two regions.

Desmosomes serve to anchor the cytoskeletons of two adjacent cells, helping with force transduction. Gap junctions allow for cellular communication by creating perforations between cells through which ions and small molecules can flow. Villi are not a type of cell junction, and are structures that serve to increase cell surface area.

Example Question #5 : Understanding Cell Junctions

Which of the following is a potential function of cell junctions?

I. Anchor adjacent cells

II. Anchor the extracellular matrix

III. Communicate with neighboring cells

Possible Answers:

I and II

I, II, and III

III only

I and III

Correct answer:

I, II, and III

Explanation:

All of the choices presented describe functions of cell junctions. Adherens junctions and desmosomes are responsible for anchoring neighboring cells to one another. Hemidesmosomes help anchor the extracellular matrix in place, binding the cell membrane to proteins in the basal lamina or matrix. Gap junctions are an example of junctions that connect the cytoplasm of two neighboring cells and allow for communication via ions and other small molecules.

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