All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
Example Questions
Example Question #1 : Cellular Junctions
Which of the following statements is NOT TRUE about gap junctions?
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 contribute to electrical coupling of adjacent cells.
Gap junctions prevent molecules and ions from traveling between cells in the extracellular space.
Gap junctions have some functionality of permitting cells to adhere to one another.
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 : Help With Junction Proteins
Which of the following proteins forms channels that permit electrical communication between cells across gap junctions?
Cadherin
Connexin
Catenin
Tubulin
Ephrin
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 : Signals, Communication, And Junctions
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 protocadherins
Claudins and adherins
Occludins and connexins
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 #2 : Cellular Junctions
What is the main purpose of gap junctions?
Prevents cells from separating from one another
Allows molecules and ions to travel between cells
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 #1 : Cellular Junctions
Which cellular junction will be most useful in preventing the movement of material between cell membranes?
Hemidesmosomes
Gap junctions
Desmosomes
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?
Epinephrine
cAMP
Receptor tyrosine kinases
G subunits of G proteins
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 #71 : Cell Biology
Which of the following signaling molecules does not elicit a second messenger response inside cells?
Large peptides
Peptide hormones
Glucagon
Steroid 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 #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?
Potassium channels close
Sodium channels are inactivated
Voltage-gated sodium channels open
The sodium-potassium pump stops
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.
Example Question #1 : Help With Action Potentials And Synapses
An action potential occurs in an axon that synapses at a muscle; this specific type of synapse is called a neuromuscular junction. During the action potential, the membrane potential of the axon sharply depolarizes as the signal moves towards the terminal. Upon reaching the synaptic terminal, neurotransmitters are released and interact with receptors on the muscle. Which of the following best summarizes the changes that occur in the post-synaptic muscle after a neurotransmission event?
Activation of receptors depletes the muscle of intracellular calcium stores and the muscle depolarizes.
Activation of receptors opens ion channels, but the membrane potential is unchanged.
Activation of receptors causes opening of ion channels on the muscle, and the muscle hyperpolarizes.
Activation of receptors causes opening of ion channels on the muscle, and the muscle depolarizes.
Activation of receptors causes closing of ion channels on the muscle, and the muscle hyperpolarizes.
Activation of receptors causes opening of ion channels on the muscle, and the muscle depolarizes.
Neurotransmitters will bind their respective receptors on the post-synaptic membrane, which is a muscle in this case. This binding causes changes to other proteins on that membrane, which results in an opening of ion channels. The muscle then depolarizes due to the influx of positively charged ions, and this can be measured as a positive change in the muscle membrane potential.
Example Question #1 : Cellular Signals And Communication
What protein is responsible for maintaining the resting potential across a neuronal plasma membrane?
Ligand-gated sodium channels
Potassium-ATP transporter
Sodium-chlorine pump
Sodium-potassium pump
Proton pump
Sodium-potassium pump
The sodium-potassium pump maintains the resting membrane potential by utilizing 1 ATP to transport 2 potassium ions into the cell, and pumping 3 sodium ions out, which makes the inside of the cell negative relative to the outside of the cell.