All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
Example Questions
Example Question #62 : Cell Biology
Adherens junctions are specialized cell junctions that form by linking the __________ to transmembrane proteins known as __________.
actin cytoskeleton . . . cadherins
microtubule cytoskeleton . . . integrins
microtubule cytoskeleton . . . cadherins
intermediate filament cytoskeleton . . . integrins
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 : Help With Junction Types
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
III and IV
I, II, and III
I and III
I, II, III, and IV
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 : Cellular Junctions
Which of the following statements is NOT TRUE about gap junctions?
Gap junctions permit the travel of small molecules back and forth between adjacent cells.
Gap junctions have some functionality of permitting cells to adhere to one another.
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 contribute to electrical coupling of 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 #2 : Cellular Junctions
Which of the following proteins forms channels that permit electrical communication between cells across gap junctions?
Catenin
Connexin
Tubulin
Ephrin
Cadherin
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 : Cellular Processes
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?
Claudins and adherins
Connexins and integrins
Occludins and connexins
Claudins and protocadherins
Claudins and occludins
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 #3 : Cellular Junctions
What is the main purpose of gap junctions?
Prevents water from moving between cells
Allows large molecules to move between cells
Allows molecules and ions to travel between cells
Prevents cells from separating from one another
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 #72 : Cell Biology
Which cellular junction will be most useful in preventing the movement of material between cell membranes?
Hemidesmosomes
Desmosomes
Gap junctions
Tight junctions
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.
Example Question #1 : Cellular Signals And Communication
Which of the following is a common second messenger used in signal transduction pathways?
Receptor tyrosine kinases
G subunits of G proteins
cAMP
Epinephrine
cAMP
Second messengers are the molecules in a signal transduction pathway that will activate an intracellular response. Epinephrine is a hormone that will bind a receptor on the exoplasmic face of the cell, making is a first messenger. G subunits interact with adaptor proteins that will then stimulate the production of second messengers. Receptor tyrosine kinases are examples of receptor proteins that will bind first messengers. cAMP, however, is a widely used second messenger that is involved in the activation of many pathways and signal amplification in the cytosol.
Example Question #2 : Help With Second Messengers
Which of the following signaling molecules does not elicit a second messenger response inside cells?
Large peptides
Glucagon
Steroid hormones
Peptide hormones
Steroid hormones
A second messenger response is created in cells that use signal transduction, meaning that the signaling molecules attach to a receptor on the outside of the cell. Steroid hormones are largely nonpolar, and can enter the cell in order to affect cellular processes at the level of transcription. As a result, they do not need to rely on second messenger pathways in order to elicit a response.
Example Question #271 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
Which of the following choices corresponds to what is happening in a cell when an action potential reaches its peak?
Voltage-gated sodium channels open
The sodium-potassium pump stops
Sodium channels are inactivated
Potassium channels close
Sodium channels are inactivated
The peak of an action potential signals the inactivation of sodium channels. This effectively prevents more sodium from entering the cell and halts the depolarization that was previously occurring, resulting in a maximum depolarization value. Potassium channels remain open, and are the cause for the membrane potential to start dropping (positive charge is leaving the cell). The sodium-potassium pump does not stop during this process. In fact, its continued function is essential for eventually restoring the resting membrane potential.
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All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
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