GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Cellular Processes

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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Example Questions

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Example Question #261 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology

Adherens junctions are specialized cell junctions that form by linking the __________ to transmembrane proteins known as __________.

Possible Answers:

actin cytoskeleton . . . cadherins

microtubule cytoskeleton . . . integrins

microtubule cytoskeleton . . . cadherins

intermediate filament cytoskeleton . . . integrins

Correct answer:

actin cytoskeleton . . . cadherins

Explanation:

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 : Signals, Communication, And 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

Possible Answers:

I, II, and III

I and III

I, II, III, and IV

III and IV

Correct answer:

I and III

Explanation:

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?

Possible Answers:

Gap junctions prevent molecules and ions from traveling between cells in the extracellular space. 

Gap junctions form channels that are comprised of connexin proteins. 

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 contribute to electrical coupling of adjacent cells. 

Correct answer:

Gap junctions prevent molecules and ions from traveling between cells in the extracellular space. 

Explanation:

"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 : Help With Junction Proteins

Which of the following proteins forms channels that permit electrical communication between cells across gap junctions? 

Possible Answers:

Ephrin

Catenin

Connexin

Cadherin

Tubulin

Correct answer:

Connexin

Explanation:

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 #271 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology

What are the two major proteins that comprise tight junctionscellular junctions that prevent fluids from traveling between cells and generally contribute to morphology by holding cells together?

Possible Answers:

Claudins and occludins

Claudins and adherins 

Connexins and integrins

Occludins and connexins

Claudins and protocadherins

Correct answer:

Claudins and occludins

Explanation:

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 : Help With Junction Functions

What is the main purpose of gap junctions?

Possible Answers:

Prevents cells from separating from one another

Prevents water from moving between cells

Allows molecules and ions to travel between cells

Allows large molecules to move between cells

Correct answer:

Allows molecules and ions to travel between cells

Explanation:

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 : Help With Junction Functions

Which cellular junction will be most useful in preventing the movement of material between cell membranes?

Possible Answers:

Desmosomes

Gap junctions

Tight junctions

Hemidesmosomes

Correct answer:

Tight junctions

Explanation:

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 #272 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology

Which of the following is a common second messenger used in signal transduction pathways?

Possible Answers:

Epinephrine

cAMP

Receptor tyrosine kinases

G subunits of G proteins

Correct answer:

cAMP

Explanation:

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 #4 : Cellular Processes

Which of the following signaling molecules does not elicit a second messenger response inside cells?

Possible Answers:

Glucagon

Peptide hormones

Steroid hormones

Large peptides

Correct answer:

Steroid hormones

Explanation:

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 #1 : Signals, Communication, And Junctions

Which of the following choices corresponds to what is happening in a cell when an action potential reaches its peak?

Possible Answers:

Sodium channels are inactivated

The sodium-potassium pump stops

Potassium channels close

Voltage-gated sodium channels open

Correct answer:

Sodium channels are inactivated

Explanation:

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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