Cellular Processes - GRE Subject Test: Biochemistry, Cell, and Molecular Biology
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Which of the following choices corresponds to what is happening in a cell when an action potential reaches its peak?
Which of the following choices corresponds to what is happening in a cell when an action potential reaches its peak?
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.
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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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?
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?
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.
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.
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Which phase of the action potential begins when there is a rapid and massive influx of sodium ions into the neuron?
Which phase of the action potential begins when there is a rapid and massive influx of sodium ions into the neuron?
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.
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.
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What protein is responsible for maintaining the resting potential across a neuronal plasma membrane?
What protein is responsible for maintaining the resting potential across a neuronal plasma membrane?
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.
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.
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RNA of Gene X was injected into the posterior of a fruit fly embryo, and the resulting embryo had two heads instead of a head and a tail. What type of protein does gene X most likely code for?
RNA of Gene X was injected into the posterior of a fruit fly embryo, and the resulting embryo had two heads instead of a head and a tail. What type of protein does gene X most likely code for?
Morphogens are proteins that can regulate the patterning of embryos over a multi-cell distance. Classic morphogens were discovered by injecting cytoplasm of embryos from the anteiror to the posterior, which would give rise to an animal with two heads. Injecting cytoplasm from the posterior to the anterior would give rise to animals with two posteriors. If injecting the RNA of a particular gene changes the patterning of the animal dramatically, it is likely a morphogen.
Morphogens are proteins that can regulate the patterning of embryos over a multi-cell distance. Classic morphogens were discovered by injecting cytoplasm of embryos from the anteiror to the posterior, which would give rise to an animal with two heads. Injecting cytoplasm from the posterior to the anterior would give rise to animals with two posteriors. If injecting the RNA of a particular gene changes the patterning of the animal dramatically, it is likely a morphogen.
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Homeobox (Hox) genes are essential regulators of development of an organism, as they define region specific development of an embryo along its anterior-posterioir axis. A mutation in the gene Antennapedia, for example, causes Drosophila melanogaster to grow legs from its head instead of antennae.
Given that hox genes regulate segmental identity of an organism, which of the following phenotypes would possibly be present in a fruit fly with a mutation in a Hox gene required for formation of very anterior structures?
Homeobox (Hox) genes are essential regulators of development of an organism, as they define region specific development of an embryo along its anterior-posterioir axis. A mutation in the gene Antennapedia, for example, causes Drosophila melanogaster to grow legs from its head instead of antennae.
Given that hox genes regulate segmental identity of an organism, which of the following phenotypes would possibly be present in a fruit fly with a mutation in a Hox gene required for formation of very anterior structures?
The only 'very anterior' structure listed among the answers is the head. If this particular hox gene is required to create the proper anterior appendage, we can predict that of the structures listed the head is most likely to be affected.
The only 'very anterior' structure listed among the answers is the head. If this particular hox gene is required to create the proper anterior appendage, we can predict that of the structures listed the head is most likely to be affected.
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HOX genes are a group of genes that have been well characterized to control body plan development along the anterior to posterior axis in developing embryos. What do HOX genes encode?
HOX genes are a group of genes that have been well characterized to control body plan development along the anterior to posterior axis in developing embryos. What do HOX genes encode?
The correct answer is transcription factors. HOX transcription factors turn on genes during embryonic development to determine the type of segment structure (examples are legs or antennae) at different spatial regions of the embryo. Absence or mis-expression of HOX genes in early development renders misinformed or non-viable organisms.
The correct answer is transcription factors. HOX transcription factors turn on genes during embryonic development to determine the type of segment structure (examples are legs or antennae) at different spatial regions of the embryo. Absence or mis-expression of HOX genes in early development renders misinformed or non-viable organisms.
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How do master regulators, which are transcription factors, establish cell subtypes and cell subtype-specific gene expression?
How do master regulators, which are transcription factors, establish cell subtypes and cell subtype-specific gene expression?
The correct answer is master regulators promote the deposition of methyl or acetyl groups to mark inactive or active enhancers. Master regulators bind enhancer regions that have been created by pioneer factors to establish the chromatin state of the cell by deposition of methyl or acetyl groups on chromatin. Methylation correlates with inactive enhancers, whereas acetylation correlates with active enhancers. The fingerprint of active/inactive enhancers and its effect on gene expression establishes cell subtypes. Some, but not all master regulators function as pioneer factors to bind nucleosome rich DNA to promote euchromatin formation.
The correct answer is master regulators promote the deposition of methyl or acetyl groups to mark inactive or active enhancers. Master regulators bind enhancer regions that have been created by pioneer factors to establish the chromatin state of the cell by deposition of methyl or acetyl groups on chromatin. Methylation correlates with inactive enhancers, whereas acetylation correlates with active enhancers. The fingerprint of active/inactive enhancers and its effect on gene expression establishes cell subtypes. Some, but not all master regulators function as pioneer factors to bind nucleosome rich DNA to promote euchromatin formation.
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The mesodermal germ layer can give rise to each of the following cell types except __________.
The mesodermal germ layer can give rise to each of the following cell types except __________.
The mesoderm gives rise to the "middle" cells that line the body, such as the muscle. The notocord is a critical embryonic structure that forms from the mesoderm, and myoblasts and fibroblasts are cells that line the body. The alveoli are part of the lung, which originates from the endodermal germ layer.
The mesoderm gives rise to the "middle" cells that line the body, such as the muscle. The notocord is a critical embryonic structure that forms from the mesoderm, and myoblasts and fibroblasts are cells that line the body. The alveoli are part of the lung, which originates from the endodermal germ layer.
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Which of the listed processes are part of gastrulation?
Which of the listed processes are part of gastrulation?
Gastrulation is the process of cells from the epiblast ingressing into the embryo to form the three germ layers of bilaterally symetrical animals. When gastrulation is complete, the embryo is referred to as a gastrula. The group of cells that lead the migration of cells into the embryo are called the primitive streak, and they undergo epithelial to mesenchymal transition to be able to migrate. You can image the epithelium as many tightly packed squares. Becomimg mesenchymal turns these cells into more malleable stage, like a soft cushion. They can then "drop" into the inner layer of the blastocyst and lead the process of gastrulation.
Gastrulation is the process of cells from the epiblast ingressing into the embryo to form the three germ layers of bilaterally symetrical animals. When gastrulation is complete, the embryo is referred to as a gastrula. The group of cells that lead the migration of cells into the embryo are called the primitive streak, and they undergo epithelial to mesenchymal transition to be able to migrate. You can image the epithelium as many tightly packed squares. Becomimg mesenchymal turns these cells into more malleable stage, like a soft cushion. They can then "drop" into the inner layer of the blastocyst and lead the process of gastrulation.
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Which of the following statements about determination is true?
Which of the following statements about determination is true?
Determination is the process of a cell committing to a particular fate and is influenced by the cell's environment as well as its own genome. It's not possible to tell the difference between an undetermined and a determined cell since determined cells do not change in appearance. After determination comes differentiation. Differentiation results from differential gene expression (transcription, mRNA splicing, and translation).
Determination is the process of a cell committing to a particular fate and is influenced by the cell's environment as well as its own genome. It's not possible to tell the difference between an undetermined and a determined cell since determined cells do not change in appearance. After determination comes differentiation. Differentiation results from differential gene expression (transcription, mRNA splicing, and translation).
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Which of the following terms describes when the single germ layered blastula reorganizes into a structure with mesoderm, endoderm, and ectoderm germ layers?
Which of the following terms describes when the single germ layered blastula reorganizes into a structure with mesoderm, endoderm, and ectoderm germ layers?
The correct answer is gastrulation. Gastrulation occurs through five stages (1. invagination 2. involution 3. ingression 4. delamination 5. epiboly) and results in the formation of a gastrula with the mesoderm, endoderm, and ectoderm germ layers. Blastulation is the formation of the single germ layered blastula, which is a process that precedes gastrulation. Somiteogenesis forms somites in developing embryos to give rise to the future spine. Myogenesis is the formation of muscle tissue. Morphogenesis is the process of an organism forming its shape, driven by cell cycle progression, differentiation, and subsequent development of organs and appendages.
The correct answer is gastrulation. Gastrulation occurs through five stages (1. invagination 2. involution 3. ingression 4. delamination 5. epiboly) and results in the formation of a gastrula with the mesoderm, endoderm, and ectoderm germ layers. Blastulation is the formation of the single germ layered blastula, which is a process that precedes gastrulation. Somiteogenesis forms somites in developing embryos to give rise to the future spine. Myogenesis is the formation of muscle tissue. Morphogenesis is the process of an organism forming its shape, driven by cell cycle progression, differentiation, and subsequent development of organs and appendages.
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Which embryonic structure is created by the process of gastrulation?
Which embryonic structure is created by the process of gastrulation?
Gastrulation is a process occurring in week three of development. At this time, the epiblast will further differentiate into three germ layers: the ectoderm, the mesoderm, and the endoderm. As a result, we can say that gastrulation allows for the creation of the mesoderm.
Gastrulation is a process occurring in week three of development. At this time, the epiblast will further differentiate into three germ layers: the ectoderm, the mesoderm, and the endoderm. As a result, we can say that gastrulation allows for the creation of the mesoderm.
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Which of the following mutations in the EGF pathway could lead to increased proliferation of cells?
Which of the following mutations in the EGF pathway could lead to increased proliferation of cells?
The phosphorylation of Erk is the final step of the protein cascade of EGF pathway, and phosphorylated Erk enters the nucleus to increase transcription of genes that induce proliferation. If Erk is constitutively active, it will likely lead to higher proliferation rate.
Preventing EGF from binding to EGFR or disrupting EGFR's ability to enter the membrane would abolish EGF pathway activity and reduce proliferation. Likewise, abolishing kinase activity of RAF would terminate the signal transduction and lead to reduced proliferation.
The phosphorylation of Erk is the final step of the protein cascade of EGF pathway, and phosphorylated Erk enters the nucleus to increase transcription of genes that induce proliferation. If Erk is constitutively active, it will likely lead to higher proliferation rate.
Preventing EGF from binding to EGFR or disrupting EGFR's ability to enter the membrane would abolish EGF pathway activity and reduce proliferation. Likewise, abolishing kinase activity of RAF would terminate the signal transduction and lead to reduced proliferation.
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Production of which of the following cytokines is stimulated when the 
concentration decreases in the circulatory system?
Production of which of the following cytokines is stimulated when the
Erythropoietin, released by the kidney, stimulates the production of red blood cells, which becomes necessary if circulating 
has decreased. Tumor necrosis factor stimulates systemic inflammation and regulates the immune system. Transforming growth factor beta 1 controls cell growth, proliferation, differentiation and other processes. Interferon type II modulates immune functions. Interleukin 2 also modulates the immune cells.
Erythropoietin, released by the kidney, stimulates the production of red blood cells, which becomes necessary if circulating
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Which of the following growth factors is primarily produced by the kidney and is essential for the production of red blood cells?
Which of the following growth factors is primarily produced by the kidney and is essential for the production of red blood cells?
Erythropoietin is a glycoprotein that is crucial for the production of red blood cells, a process also called "erythropoiesis." Each of the other answers contains a growth factor, but none of these have a primary function in red blood cell production.
Erythropoietin is a glycoprotein that is crucial for the production of red blood cells, a process also called "erythropoiesis." Each of the other answers contains a growth factor, but none of these have a primary function in red blood cell production.
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Which of the following hormones will elicit a response in cells by attaching to a membrane bound receptor?
Which of the following hormones will elicit a response in cells by attaching to a membrane bound receptor?
Before answering this question, consider what types of hormones would not attach to a membrane bound receptor. Steroid hormones can simply diffuse through the plasma membrane, so they do not need to attach to a receptor there. Cortisol, testosterone, and estrogen are all steroid hormones. This leaves insulin as the only acceptable answer. In fact, insulin attaches to a receptor tyrosine kinase on the outside of cells.
Before answering this question, consider what types of hormones would not attach to a membrane bound receptor. Steroid hormones can simply diffuse through the plasma membrane, so they do not need to attach to a receptor there. Cortisol, testosterone, and estrogen are all steroid hormones. This leaves insulin as the only acceptable answer. In fact, insulin attaches to a receptor tyrosine kinase on the outside of cells.
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What is the main purpose of gap junctions?
What is the main purpose of gap junctions?
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.
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.
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Which cellular junction will be most useful in preventing the movement of material between cell membranes?
Which cellular junction will be most useful in preventing the movement of material between cell membranes?
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.
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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Which of the following proteins forms channels that permit electrical communication between cells across gap junctions?
Which of the following proteins forms channels that permit electrical communication between cells across gap junctions?
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.
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.
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