All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
Example Questions
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.
Example Question #1 : Cellular Signals And Communication
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 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 depletes the muscle of intracellular calcium stores and the muscle depolarizes.
Activation of receptors causes closing of ion channels on the muscle, and the muscle hyperpolarizes.
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 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 : Help With Action Potentials And Synapses
What protein is responsible for maintaining the resting potential across a neuronal plasma membrane?
Sodium-chlorine pump
Sodium-potassium pump
Proton pump
Ligand-gated sodium channels
Potassium-ATP transporter
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.
Example Question #2 : Help With Action Potentials And Synapses
Which phase of the action potential begins when there is a rapid and massive influx of sodium ions into the neuron?
Hyperpolarization
Undershoot
Repolarization
Overshoot
Depolarization
Depolarization
Depolarization, also known as the rising phase, occurs when the membrane potential goes from being negative to positive very quickly. This is instigated by the influx of ions through the open voltage gated channels, and the positive ions make the cell more positive relative to the resting potential.
Example Question #1 : Help With Receptors And Channels
Toll-like receptors (TLRs) are transmembrane receptors that have an extracellular leucine-rich region and an intracellular toll-interleukin region domain. What is the primary function of TLRs?
Bind epidermal growth factor to promote cell proliferation
Elicit innate immune responses by recognizing microbial associated molecular patterns
Promote sex-specific organ growth by binding estrogen or testosterone
Promote cell-cell adhesion
Promote differentiation by recognizing notch ligands
Elicit innate immune responses by recognizing microbial associated molecular patterns
The correct answer is elicit innate immune responses by recognizing microbial associated molecular patterns. TLRs are pattern recognition transmembrane receptors that recognize bacterial components, such as lipopolysaccharides and flagellin, and viral components such as single stranded DNA. Upon recognition by the leucine rich region, TLRs dimerize to facilitate signal transduction (via the toll-interleukin region domain) to downstream pathways to promote inflammation and recruitment of macrophages.
Example Question #2 : Help With Receptors And Channels
Which of the following is not true concerning G protein-coupled receptors (GPCRs)?
They use GTP as energy when activated.
They are found on the outside of cell membranes.
They can recognize peptide hormones as their ligand.
All GPCRs will increase cAMP levels in the cell.
All GPCRs will increase cAMP levels in the cell.
G protein coupled receptors are by far the largest class of cell surface receptors. They can respond to a large variety of extracellular signaling molecules, and can elicit a great deal of responses inside cells. With such diversity, it should come as no surprise that not all GPCRs will increase cAMP levels in the cell. In fact, many can display an inhibitory role, and decrease cAMP levels by preventing its production.
Example Question #3 : Help With Receptors And Channels
The sodium-potassium pump works by bringing sodium __________ cells and potassium __________ cells through the use of ATP.
into . . . into
None of these
out of . . . out of
into . . . out of
out of . . . into
out of . . . into
The sodium-potassium pump is a type of active transport that brings sodium out of the cell and potassium into the cell. This is in the opposite direction of their natural gradient. The fact that it is going in the opposite direction requires this pump to need energy, or, ATP.
Example Question #1 : Help With Signal Transduction
Which of the following events occur when the MAP Kinase pathway is activated?
Ras blocks the activation of MAP kinases
The receptor is phosphorylated by G-coupled proteins
The phosphorylated receptor facilitates the binding of GDP to Ras
ATP is used to phosphorylate transcription factors
ATP is used to phosphorylate transcription factors
When MAP Kinase signaling is activated, the receptors auto-phosphorylate to activate the signal transduction, which leads to the binding of GTP to Ras. Ras is activated when bound to GTP. Ras then activates downstream MAP Kinases, which lead to a phosphorylate cascade that eventually uses ATP to phosphorylate transcription factors. The phosphorylated transcription factors then go on to alter gene expression in the cell.
Therefore, the correct answer in this question is that transcription factors are phosphorylated using ATP molecules.
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All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
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