GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Cellular Junctions
Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology
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Example Questions
Example Question #1 : Signals, Communication, And Junctions
Adherens junctions are specialized cell junctions that form by linking the __________ to transmembrane proteins known as __________.
intermediate filament cytoskeleton . . . integrins
microtubule cytoskeleton . . . integrins
actin cytoskeleton . . . cadherins
microtubule cytoskeleton . . . cadherins
actin cytoskeleton . . . cadherins
Adherens junctions are formed by linking the actin cytoskeleton to transmembrane proteins known as cadherins. Cadherins are capable of interacting with other cadherins from neighboring cells on the exoplasmic face of the cell membrane. This interaction forms a physical link essentially connecting the actin cytoskeletons of the two adjacent cells, thus promoting force transduction.
Desmosomes are another type of cell junction that link the intermediate filaments of the cytoskeleton to cadherins.
Example Question #1 : Cellular Junctions
Which of the following cell junctions is involved with anchoring the extracellular matrix to the cell?
I. Adherens junctions
II. Desmosomes
III. Hemidesmosomes
IV. Gap junctions
I, II, III, and IV
III and IV
I, II, and III
I and III
I and III
Of the choices, only adherens junctions and hemidesmosomes are responsible for anchoring the extracellular matrix. This is accomplished by associating the actin cytoskeleton (for adherens junctions) or the intermediate filament cytoskeleton (for hemidesmosomes) with transmembrane proteins known as integrins. Integrins interact with the extracellular matrix.
Desmosomes are responsible for anchoring adjacent cells to one another by connecting their intermediate filament cytoskeletons with cadherins. Gap junctions connect the cytoplasm of adjacent cells and allow the free flow of small molecules between them.
Example Question #1 : Signals, Communication, And Junctions
Which of the following statements is NOT TRUE about gap junctions?
Gap junctions have some functionality of permitting cells to adhere to one another.
Gap junctions contribute to electrical coupling of adjacent cells.
Gap junctions form channels that are comprised of connexin proteins.
Gap junctions prevent molecules and ions from traveling between cells in the extracellular space.
Gap junctions permit the travel of small molecules back and forth between adjacent cells.
Gap junctions prevent molecules and ions from traveling between cells in the extracellular space.
"Gap junctions prevent molecules and ions from traveling between cells in the extracellular space" is incorrect because this describes the function of tight junctions. Gap junctions electrically couple two cells by permitting the formation of small channels that connect two cells.
Example Question #1 : Cellular Junctions
Which of the following proteins forms channels that permit electrical communication between cells across gap junctions?
Ephrin
Cadherin
Tubulin
Catenin
Connexin
Connexin
Most of the other proteins listed are structural, but do not form any kind of pore or channel through which an electrical message can cross. Connexins are required for this function of gap junctions.
Example Question #1 : Help With Junction Proteins
What are the two major proteins that comprise tight junctions, cellular junctions that prevent fluids from traveling between cells and generally contribute to morphology by holding cells together?
Connexins and integrins
Claudins and adherins
Claudins and occludins
Claudins and protocadherins
Occludins and connexins
Claudins and occludins
While each of the proteins listed contribute to cell structure and function, the tight junction requires claudins and occludins to anchor the cytoskeleton of two adjacent cells to one another. These are the primary structural components of tight junctions.
Example Question #1 : Cellular Junctions
What is the main purpose of gap junctions?
Allows molecules and ions to travel between cells
Prevents cells from separating from one another
Allows large molecules to move between cells
Prevents water from moving between cells
Allows molecules and ions to travel between cells
Gap junctions can be thought of as small tunnels between cells. They allow for the immediate transport of ions and molecules between the cells. Gap junctions are prominent in cardiac myocytes, and help spread action potentials via electrical synapses to coordinate the contraction of the heart.
Example Question #2 : Signals, Communication, And Junctions
Which cellular junction will be most useful in preventing the movement of material between cell membranes?
Hemidesmosomes
Tight junctions
Gap junctions
Desmosomes
Tight junctions
The movement of substances between cells is most commonly controlled by tight junctions. These junctions can be regulated, which can alter how strongly they resist the movement of material between cells, like those in the digestive tract during absorption.
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