Cell Biology, Molecular Biology, and Genetics - MCAT Biology
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During which of the following portions of the cell cycle is DNA polymerase most active?
During which of the following portions of the cell cycle is DNA polymerase most active?
By referring to DNA polymerase activity, this question is asking about the portion of the cell cycle that involves DNA replication. S phase is the portion of Interphase during which the cell replicates its DNA.
By referring to DNA polymerase activity, this question is asking about the portion of the cell cycle that involves DNA replication. S phase is the portion of Interphase during which the cell replicates its DNA.
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During which of the following portions of the cell cycle are mRNA and proteins mainly produced?
During which of the following portions of the cell cycle are mRNA and proteins mainly produced?
By referring to mRNA and proteins, this question is asking about the portion of the cell cycle that involves gene transcription and protein translation. This occurs mostly during growth and organelle replication in the G1 portion of Interphase.
By referring to mRNA and proteins, this question is asking about the portion of the cell cycle that involves gene transcription and protein translation. This occurs mostly during growth and organelle replication in the G1 portion of Interphase.
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Human chromosomes are divided into two arms, a long q arm and a short p arm. A karyotype is the organization of a human cell’s total genetic complement. A typical karyotype is generated by ordering chromosome 1 to chromosome 23 in order of decreasing size.
When viewing a karyotype, it can often become apparent that changes in chromosome number, arrangement, or structure are present. Among the most common genetic changes are Robertsonian translocations, involving transposition of chromosomal material between long arms of certain chromosomes to form one derivative chromosome. Chromosomes 14 and 21, for example, often undergo a Robertsonian translocation, as below.
A karyotype of this individual for chromosomes 14 and 21 would thus appear as follows:
Though an individual with aberrations such as a Robertsonian translocation may be phenotypically normal, they can generate gametes through meiosis that have atypical organizations of chromosomes, resulting in recurrent fetal abnormalities or miscarriages.
Chromosomes are often made visible using Giemsa staining. This stain shows specific banding patterns for chromosomes, and helps scientists organize them under a microscope. Considering that chromosomes are the standard unit of organization for a cell’s DNA, during which phase of the cell cycle would chromosomes most likely be visible?
Human chromosomes are divided into two arms, a long q arm and a short p arm. A karyotype is the organization of a human cell’s total genetic complement. A typical karyotype is generated by ordering chromosome 1 to chromosome 23 in order of decreasing size.
When viewing a karyotype, it can often become apparent that changes in chromosome number, arrangement, or structure are present. Among the most common genetic changes are Robertsonian translocations, involving transposition of chromosomal material between long arms of certain chromosomes to form one derivative chromosome. Chromosomes 14 and 21, for example, often undergo a Robertsonian translocation, as below.
A karyotype of this individual for chromosomes 14 and 21 would thus appear as follows:
Though an individual with aberrations such as a Robertsonian translocation may be phenotypically normal, they can generate gametes through meiosis that have atypical organizations of chromosomes, resulting in recurrent fetal abnormalities or miscarriages.
Chromosomes are often made visible using Giemsa staining. This stain shows specific banding patterns for chromosomes, and helps scientists organize them under a microscope. Considering that chromosomes are the standard unit of organization for a cell’s DNA, during which phase of the cell cycle would chromosomes most likely be visible?
Chromosomes are most likely to be visible when a cell is organizing its genetic material, as it would just before it undergoes cytokinesis and becomes two daughter cells. S phase is a tempting answer, as this is when DNA is duplicated, but S phase only encompasses the enzymatic replication of DNA, and not its organization which is characteristic of the much shorter M phase.
Chromosomes are most likely to be visible when a cell is organizing its genetic material, as it would just before it undergoes cytokinesis and becomes two daughter cells. S phase is a tempting answer, as this is when DNA is duplicated, but S phase only encompasses the enzymatic replication of DNA, and not its organization which is characteristic of the much shorter M phase.
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Scientists use a process called Flourescent In-Situ Hybridization, or FISH, to study genetic disorders in humans. FISH is a technique that uses spectrographic analysis to determine the presence or absence, as well as the relative abundance, of genetic material in human cells.
To use FISH, scientists apply fluorescently-labeled bits of DNA of a known color, called probes, to samples of test DNA. These probes anneal to the sample DNA, and scientists can read the colors that result using laboratory equipment. One common use of FISH is to determine the presence of extra DNA in conditions of aneuploidy, a state in which a human cell has an abnormal number of chromosomes. Chromosomes are collections of DNA, the totality of which makes up a cell’s genome. Another typical use is in the study of cancer cells, where scientists use FISH labels to ascertain if genes have moved inappropriately in a cell’s genome.
Using red fluorescent tags, scientists label probe DNA for a gene known to be expressed more heavily in cancer cells than normal cells. They then label a probe for an immediately adjacent DNA sequence with a green fluorescent tag. Both probes are then added to three dishes, shown below. In dish 1 human bladder cells are incubated with the probes, in dish 2 human epithelial cells are incubated, and in dish 3 known non-cancerous cells are used. The relative luminescence observed in regions of interest in all dishes is shown below.
If the bladder cells are experiencing uncontrolled division in dish 1, they are likely spending abnormally long periods of time in which phase of the cell cycle?
Scientists use a process called Flourescent In-Situ Hybridization, or FISH, to study genetic disorders in humans. FISH is a technique that uses spectrographic analysis to determine the presence or absence, as well as the relative abundance, of genetic material in human cells.
To use FISH, scientists apply fluorescently-labeled bits of DNA of a known color, called probes, to samples of test DNA. These probes anneal to the sample DNA, and scientists can read the colors that result using laboratory equipment. One common use of FISH is to determine the presence of extra DNA in conditions of aneuploidy, a state in which a human cell has an abnormal number of chromosomes. Chromosomes are collections of DNA, the totality of which makes up a cell’s genome. Another typical use is in the study of cancer cells, where scientists use FISH labels to ascertain if genes have moved inappropriately in a cell’s genome.
Using red fluorescent tags, scientists label probe DNA for a gene known to be expressed more heavily in cancer cells than normal cells. They then label a probe for an immediately adjacent DNA sequence with a green fluorescent tag. Both probes are then added to three dishes, shown below. In dish 1 human bladder cells are incubated with the probes, in dish 2 human epithelial cells are incubated, and in dish 3 known non-cancerous cells are used. The relative luminescence observed in regions of interest in all dishes is shown below.
If the bladder cells are experiencing uncontrolled division in dish 1, they are likely spending abnormally long periods of time in which phase of the cell cycle?
Cell division occurs in M phase. Thus, if the cells are experiencing uncontrolled growth, they are probably remaining in M phase abnormally long.
Cell division occurs in M phase. Thus, if the cells are experiencing uncontrolled growth, they are probably remaining in M phase abnormally long.
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During the eukaryotic cell cycle, what is the purpose of the G2/M checkpoint?
During the eukaryotic cell cycle, what is the purpose of the G2/M checkpoint?
The G2 phase occurs after S phase, but before M phase (mitosis). The purpose of the G2/M check point is to ensure there is no DNA damage that occurred during S phase (DNA synthesis). If damage is found, the cell will try to repair and DNA breaks. If the DNA cannot be repaired, the cell will undergo apoptosis. Many cancer suppressor genes, such as p53, are involved in this process of checking the DNA quality.
The G2 phase occurs after S phase, but before M phase (mitosis). The purpose of the G2/M check point is to ensure there is no DNA damage that occurred during S phase (DNA synthesis). If damage is found, the cell will try to repair and DNA breaks. If the DNA cannot be repaired, the cell will undergo apoptosis. Many cancer suppressor genes, such as p53, are involved in this process of checking the DNA quality.
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In 2013, scientists linked a cellular response called the unfolded protein response (UPR) to a series of neurodegenerative diseases, including such major health issues as Parkinson’s and Alzheimer’s Disease. According to their work, the unfolded protein response is a reduction in translation as a result of a series of enzymes that modify a translation initiation factor, eIF2, as below:
In the above sequence, the unfolded protein sensor binds to unfolded protein, such as the pathogenic amyloid-beta found in the brains of Alzheimer’s Disease patients. This sensor then phosphorylates PERK, or protein kinase RNA-like endoplasmic reticulum kinase. This leads to downstream effects on eIF2, inhibition of which represses translation. It is thought that symptoms of neurodegenerative disease may be a result of this reduced translation.
Which of the following times in the cell cycle is the activity of eIF2 likely to be highest?
In 2013, scientists linked a cellular response called the unfolded protein response (UPR) to a series of neurodegenerative diseases, including such major health issues as Parkinson’s and Alzheimer’s Disease. According to their work, the unfolded protein response is a reduction in translation as a result of a series of enzymes that modify a translation initiation factor, eIF2, as below:
In the above sequence, the unfolded protein sensor binds to unfolded protein, such as the pathogenic amyloid-beta found in the brains of Alzheimer’s Disease patients. This sensor then phosphorylates PERK, or protein kinase RNA-like endoplasmic reticulum kinase. This leads to downstream effects on eIF2, inhibition of which represses translation. It is thought that symptoms of neurodegenerative disease may be a result of this reduced translation.
Which of the following times in the cell cycle is the activity of eIF2 likely to be highest?
We know that inhibition of eIF2 represses translation. The question asks for the time when eIF2 is most active, thus the time when translation is likely at its highest.
In M phase, the cell is actively dividing. That may make this a tempting answer, but G1 is actually when all of the non-genetic material is doubled. S phase sees the doubling of the genetic complement, and G2 is a major checkpoint stage to ensure everything is ready to go for mitosis.
G1 is the best answer, as this is the period when organelles and cellular proteins are being synthesized.
We know that inhibition of eIF2 represses translation. The question asks for the time when eIF2 is most active, thus the time when translation is likely at its highest.
In M phase, the cell is actively dividing. That may make this a tempting answer, but G1 is actually when all of the non-genetic material is doubled. S phase sees the doubling of the genetic complement, and G2 is a major checkpoint stage to ensure everything is ready to go for mitosis.
G1 is the best answer, as this is the period when organelles and cellular proteins are being synthesized.
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There are several methods for analyzing the number of cells undergoing proliferation. Cells or whole organisms can be treated with BrdU, a uracil analog, which is incorporated during DNA synthesis. Cells or tissues can be fixed and BrdU can be detected using BrdU-specific antibodies. Similarly, cells can be fixed without any pretreatment, and proliferation can be detected by antibodies specific for MKI67 or pH3 (phosphorylated histone 3). MKI67 can be detected at all active phases of the cell cycle (not interphase) while pH3 can be detected during mitosis only.
Which detection method should be used to detect the greatest number of healthy cells?
There are several methods for analyzing the number of cells undergoing proliferation. Cells or whole organisms can be treated with BrdU, a uracil analog, which is incorporated during DNA synthesis. Cells or tissues can be fixed and BrdU can be detected using BrdU-specific antibodies. Similarly, cells can be fixed without any pretreatment, and proliferation can be detected by antibodies specific for MKI67 or pH3 (phosphorylated histone 3). MKI67 can be detected at all active phases of the cell cycle (not interphase) while pH3 can be detected during mitosis only.
Which detection method should be used to detect the greatest number of healthy cells?
Because cells can be treated with BrdU in advance of analysis, a large window of time can be analyzed. MKI67 and pH3 only measure proliferation at a "snapshot" of time.
BrdU analysis will essentially provide a total number of cells that are capable of proliferating since the initial treatment with BrdU. Any cells that have undergone DNA replication since this addition will be detected, while quiescent or dead cells will not be detected. In contrast, MK167 and pH3 will show only cells that are in the act of proliferation when the sample is taken. Normally replicating cells that are simply in interphase will not be detected, even though they are healthy.
Because cells can be treated with BrdU in advance of analysis, a large window of time can be analyzed. MKI67 and pH3 only measure proliferation at a "snapshot" of time.
BrdU analysis will essentially provide a total number of cells that are capable of proliferating since the initial treatment with BrdU. Any cells that have undergone DNA replication since this addition will be detected, while quiescent or dead cells will not be detected. In contrast, MK167 and pH3 will show only cells that are in the act of proliferation when the sample is taken. Normally replicating cells that are simply in interphase will not be detected, even though they are healthy.
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Which of the following factors might cause cell cycle growth arrest?
Which of the following factors might cause cell cycle growth arrest?
All of the choices are potential reasons for cell cycle arrest.
DNA damage activates pathways (commonly through the protein p53) in an attempt to repair the damage or activate apoptotic pathways if the DNA damage cannot be fixed. This causes arrest of the cell cycle at the G2 checkpoint.
Lack of appropriate growth factors will keep the cell from progressing through the cell cycle. Prolonged lack of growth is sometimes referred to as G0 of the cell cycle, and occurs when the cell cannot pass the G1 checkpoint.
Failure to properly align the chromosomes along the equatorial plate during mitosis will prevent the cell from activating pathways to degrade the cohesin that holds the sister chromatids together. This is a method to ensure proper segregation of chromosomes, and is known as the metaphase checkpoint.
All of the choices are potential reasons for cell cycle arrest.
DNA damage activates pathways (commonly through the protein p53) in an attempt to repair the damage or activate apoptotic pathways if the DNA damage cannot be fixed. This causes arrest of the cell cycle at the G2 checkpoint.
Lack of appropriate growth factors will keep the cell from progressing through the cell cycle. Prolonged lack of growth is sometimes referred to as G0 of the cell cycle, and occurs when the cell cannot pass the G1 checkpoint.
Failure to properly align the chromosomes along the equatorial plate during mitosis will prevent the cell from activating pathways to degrade the cohesin that holds the sister chromatids together. This is a method to ensure proper segregation of chromosomes, and is known as the metaphase checkpoint.
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Which of the following choices will be affected by a cell containing a nonfunctional copy of the protein p53?
I. Apoptotic pathways
II. DNA repair pathways
III. Ability to arrest the cell cycle
Which of the following choices will be affected by a cell containing a nonfunctional copy of the protein p53?
I. Apoptotic pathways
II. DNA repair pathways
III. Ability to arrest the cell cycle
p53 is sometimes referred to as "the guardian of the genome" due to its huge role in suppressing the propagation of cells containing permanent DNA damage. If DNA damage is detected, p53 becomes activated and acts to promote cell cycle arrest. This gives the cell a chance to repair its genome by activating the appropriate DNA repair pathways (for which p53 is also responsible).
p53 also plays a role in promoting apoptosis. If the DNA damage is irreparable, the cell will go through apoptosis to prevent propagation of this damage.
Damage to the p53 gene can lead to unmitigated cell division and tumor formation, marking p53 as a proto-oncogene.
p53 is sometimes referred to as "the guardian of the genome" due to its huge role in suppressing the propagation of cells containing permanent DNA damage. If DNA damage is detected, p53 becomes activated and acts to promote cell cycle arrest. This gives the cell a chance to repair its genome by activating the appropriate DNA repair pathways (for which p53 is also responsible).
p53 also plays a role in promoting apoptosis. If the DNA damage is irreparable, the cell will go through apoptosis to prevent propagation of this damage.
Damage to the p53 gene can lead to unmitigated cell division and tumor formation, marking p53 as a proto-oncogene.
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Which process does not occur in the pachytene phase of prophase I?
Which process does not occur in the pachytene phase of prophase I?
During the pachytene stage of prophase I in meiosis, chromosomes have become condensed and form synapses. This is also when crossover, which is important to genetic diversity, takes place.
Tetrads do not move toward the midline until later in the meiotic processes.
During the pachytene stage of prophase I in meiosis, chromosomes have become condensed and form synapses. This is also when crossover, which is important to genetic diversity, takes place.
Tetrads do not move toward the midline until later in the meiotic processes.
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The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.
Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer.
Which of the following is/are true regarding the cell cycle?
The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.
Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer.
Which of the following is/are true regarding the cell cycle?
There are four main phases in the cell cycle: G1 phase, S phase, G2 phase, and mitosis (M phase). G1 involves cell growth and preparation for DNA replication, S phase involves replication of the genetic material (DNA), G2 phase involves more cell growth and preparation for mitosis, and mitosis involves the division of the cell into two identical daughter cells. G0 phase is another phase that cells can undergo where they remain quiescent. This phase usually occurs after mitosis, when the cell is preparing to enter the G1 phase. Genetic material is increased in S phase only and cell growth occurs in G1 and G2 phases only, thus two of the answer choices are correct.
There are four main phases in the cell cycle: G1 phase, S phase, G2 phase, and mitosis (M phase). G1 involves cell growth and preparation for DNA replication, S phase involves replication of the genetic material (DNA), G2 phase involves more cell growth and preparation for mitosis, and mitosis involves the division of the cell into two identical daughter cells. G0 phase is another phase that cells can undergo where they remain quiescent. This phase usually occurs after mitosis, when the cell is preparing to enter the G1 phase. Genetic material is increased in S phase only and cell growth occurs in G1 and G2 phases only, thus two of the answer choices are correct.
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The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.
Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer.
A researcher is analyzing a molecule that stops the progression of the cell cycle. What could be the identity of this molecule?
The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.
Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer.
A researcher is analyzing a molecule that stops the progression of the cell cycle. What could be the identity of this molecule?
Progression through the cell cycle involves several molecules. There are several checkpoints along the cell cycle to ensure that the cell is ready for the next phase. One of the most important molecules involved in this process are the cyclin-dependent kinases (CDKs). These molecules phosphorylate and activate molecules that are important for the cell cycle. Inhibiting CDKs by an inhibitor will halt the activity of these molecules and, subsequently, the progression of the cell cycle.
DNA polymerase is an enzyme involved in DNA replication. It promotes DNA replication and helps the cell progress through the cell cycle. p53 is a tumor suppressor gene that is important for halting uncontrolled growth of cells. This is one of the most common mutated genes found in tumors. Lack of p53 activity leads to decreased regulation of cell growth. This means that cells can proliferate uncontrollably and can eventually become tumors.
Progression through the cell cycle involves several molecules. There are several checkpoints along the cell cycle to ensure that the cell is ready for the next phase. One of the most important molecules involved in this process are the cyclin-dependent kinases (CDKs). These molecules phosphorylate and activate molecules that are important for the cell cycle. Inhibiting CDKs by an inhibitor will halt the activity of these molecules and, subsequently, the progression of the cell cycle.
DNA polymerase is an enzyme involved in DNA replication. It promotes DNA replication and helps the cell progress through the cell cycle. p53 is a tumor suppressor gene that is important for halting uncontrolled growth of cells. This is one of the most common mutated genes found in tumors. Lack of p53 activity leads to decreased regulation of cell growth. This means that cells can proliferate uncontrollably and can eventually become tumors.
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The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.
Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer.
Which of the following phase(s) is/are not preceded by a checkpoint?
The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.
Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer.
Which of the following phase(s) is/are not preceded by a checkpoint?
There are three main checkpoints in the cell cycle. The first checkpoint occurs between G1 and S phase. During this checkpoint, the cell checks the stability of DNA molecules and the machinery required for DNA replication. If everything is fine, then the cell progresses into the S phase for DNA replication. The second checkpoint occurs between G2 phase and mitosis. During this checkpoint, the cell checks whether DNA replication occurred properly and whether the cell is ready for cell division. The third and final checkpoint occurs between the metaphase and anaphase of the cell. During this checkpoint, the cell checks whether the spindle apparatus is properly formed for anaphase and subsequent steps in mitosis.
There are three main checkpoints in the cell cycle. The first checkpoint occurs between G1 and S phase. During this checkpoint, the cell checks the stability of DNA molecules and the machinery required for DNA replication. If everything is fine, then the cell progresses into the S phase for DNA replication. The second checkpoint occurs between G2 phase and mitosis. During this checkpoint, the cell checks whether DNA replication occurred properly and whether the cell is ready for cell division. The third and final checkpoint occurs between the metaphase and anaphase of the cell. During this checkpoint, the cell checks whether the spindle apparatus is properly formed for anaphase and subsequent steps in mitosis.
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The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.
Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer.
An organism is found to have a diploid number of 50. How many chromosomes will this organism have at the end of S phase?
The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.
Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer.
An organism is found to have a diploid number of 50. How many chromosomes will this organism have at the end of S phase?
DNA replication occurs during the S phase. Upon completion of DNA replication, a cell has a duplicate copy of every chromosome it possesses. Recall that humans have 2 sets of 23 chromosomes (total of 46 chromosomes). For example, there are two different copies of chromosome 1, two different copies of chromosome 2, etc. The two different copies of chromosomes are termed homologous chromosomes. Upon completion of DNA replication, each of these 46 chromosomes will have an identical duplicate copy, called the sister chromatid. The sister chromatid is attached to the original chromosome at the centromere. This entire entity, however, is still considered a single chromosome; therefore, upon completion of S phase humans will have 46 chromosomes.
The organism in the question has 50 chromosomes to begin S phase (2n = 50); therefore, it will have 50 chromosomes at the end of S phase.
DNA replication occurs during the S phase. Upon completion of DNA replication, a cell has a duplicate copy of every chromosome it possesses. Recall that humans have 2 sets of 23 chromosomes (total of 46 chromosomes). For example, there are two different copies of chromosome 1, two different copies of chromosome 2, etc. The two different copies of chromosomes are termed homologous chromosomes. Upon completion of DNA replication, each of these 46 chromosomes will have an identical duplicate copy, called the sister chromatid. The sister chromatid is attached to the original chromosome at the centromere. This entire entity, however, is still considered a single chromosome; therefore, upon completion of S phase humans will have 46 chromosomes.
The organism in the question has 50 chromosomes to begin S phase (2n = 50); therefore, it will have 50 chromosomes at the end of S phase.
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The central nervous system consists of the brain and the spinal cord. In general, tracts allow for the brain to communicate up and down with the spinal cord. The commissures allow for the two hemispheres of the brain to communicate with each other. One of the most important commissures is the corpus callosum. The association fibers allow for the anterior regions of the brain to communicate with the posterior regions. One of the evolved routes from the spinal cord to the brain is via the dorsal column pathway. This route allows for fine touch, vibration, proprioception and 2 points discrimination. This pathway is much faster than the pain route. From the lower limbs, the signal ascends to the brain via a region called the gracile fasciculus. From the upper limbs, the signal ascends via the cuneate fasciculus region in the spinal cord.
One of the difficulties in treating spinal injuries is the inability to promote neural cells to regenerate. During which stage of the cell cycle are neural cells arrested in?
The central nervous system consists of the brain and the spinal cord. In general, tracts allow for the brain to communicate up and down with the spinal cord. The commissures allow for the two hemispheres of the brain to communicate with each other. One of the most important commissures is the corpus callosum. The association fibers allow for the anterior regions of the brain to communicate with the posterior regions. One of the evolved routes from the spinal cord to the brain is via the dorsal column pathway. This route allows for fine touch, vibration, proprioception and 2 points discrimination. This pathway is much faster than the pain route. From the lower limbs, the signal ascends to the brain via a region called the gracile fasciculus. From the upper limbs, the signal ascends via the cuneate fasciculus region in the spinal cord.
One of the difficulties in treating spinal injuries is the inability to promote neural cells to regenerate. During which stage of the cell cycle are neural cells arrested in?
Neural Cells are arrested in the 
phase to prevent growth. This arresting phase prevents abnormal growth and cancer cells development. 
and 
involve cell growth and duplication of organelles. 
phase is the time in which DNA is duplicated, and 
phase stands for mitosis, or meiosis, in which the nucleus divides.
Neural Cells are arrested in the
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In 2013, scientists linked a cellular response called the unfolded protein response (UPR) to a series of neurodegenerative diseases, including such major health issues as Parkinson’s and Alzheimer’s Disease. According to their work, the unfolded protein response is a reduction in translation as a result of a series of enzymes that modify a translation initiation factor, eIF2, as below:
In the above sequence, the unfolded protein sensor binds to unfolded protein, such as the pathogenic amyloid-beta found in the brains of Alzheimer’s Disease patients. This sensor then phosphorylates PERK, or protein kinase RNA-like endoplasmic reticulum kinase. This leads to downstream effects on eIF2, inhibition of which represses translation. It is thought that symptoms of neurodegenerative disease may be a result of this reduced translation.
Some evidence shows that the unfolded protein response can be promoted by an inflammatory state. Cytokines are released from cells exposed to stress, thus inducing the unfolded protein response in neighboring cells. Which of the following best defines this process?
In 2013, scientists linked a cellular response called the unfolded protein response (UPR) to a series of neurodegenerative diseases, including such major health issues as Parkinson’s and Alzheimer’s Disease. According to their work, the unfolded protein response is a reduction in translation as a result of a series of enzymes that modify a translation initiation factor, eIF2, as below:
In the above sequence, the unfolded protein sensor binds to unfolded protein, such as the pathogenic amyloid-beta found in the brains of Alzheimer’s Disease patients. This sensor then phosphorylates PERK, or protein kinase RNA-like endoplasmic reticulum kinase. This leads to downstream effects on eIF2, inhibition of which represses translation. It is thought that symptoms of neurodegenerative disease may be a result of this reduced translation.
Some evidence shows that the unfolded protein response can be promoted by an inflammatory state. Cytokines are released from cells exposed to stress, thus inducing the unfolded protein response in neighboring cells. Which of the following best defines this process?
Paracrine signaling is the communication between neighboring cells, such as the process described in the question. Autocrine signaling is the use of chemical mediators to activate the same cell that secreted the mediator. Endocrine signaling is the use of chemical mediators to communicate with distant cell targets.
Isotype is not a form of signal, and refers to similar structures. Autologous tissues refer to tissues taken from the same individual, and is also not a form of signaling.
Paracrine signaling is the communication between neighboring cells, such as the process described in the question. Autocrine signaling is the use of chemical mediators to activate the same cell that secreted the mediator. Endocrine signaling is the use of chemical mediators to communicate with distant cell targets.
Isotype is not a form of signal, and refers to similar structures. Autologous tissues refer to tissues taken from the same individual, and is also not a form of signaling.
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Type 1 diabetes is a well-understood autoimmune disease. Autoimmune diseases result from an immune system-mediated attack on one’s own body tissues. In normal development, an organ called the thymus introduces immune cells to the body’s normal proteins. This process is called negative selection, as those immune cells that recognize normal proteins are deleted. If cells evade this process, those that recognize normal proteins enter into circulation, where they can attack body tissues. The thymus is also important for activating T-cells that recognize foreign proteins.
As the figure below shows, immune cells typically originate in the bone marrow. Some immune cells, called T-cells, then go to the thymus for negative selection. Those that survive negative selection, enter into general circulation to fight infection. Other cells, called B-cells, directly enter general circulation from the bone marrow. It is a breakdown in this carefully orchestrated process that leads to autoimmune disease, such as type 1 diabetes.
Unlike T-cells and B-cells, macrophages use phagocytosis and digestion as their principal functions. Macrophages are directed to the site of infection by chemical mediators, such as chemokines and cytokines. These mediators react with surface proteins on macrophages and induce intracellular changes, driving the macrophages to the site of infection. Which of the following is likely true of this form of cell signaling?
I. It is mediated by an intracellular second messenger
II. It exclusively mediates changes in gene expression in the macrophage
III. It drives intracellular changes to occur over several days or weeks
IV. It is an example of autocrine signaling
Type 1 diabetes is a well-understood autoimmune disease. Autoimmune diseases result from an immune system-mediated attack on one’s own body tissues. In normal development, an organ called the thymus introduces immune cells to the body’s normal proteins. This process is called negative selection, as those immune cells that recognize normal proteins are deleted. If cells evade this process, those that recognize normal proteins enter into circulation, where they can attack body tissues. The thymus is also important for activating T-cells that recognize foreign proteins.
As the figure below shows, immune cells typically originate in the bone marrow. Some immune cells, called T-cells, then go to the thymus for negative selection. Those that survive negative selection, enter into general circulation to fight infection. Other cells, called B-cells, directly enter general circulation from the bone marrow. It is a breakdown in this carefully orchestrated process that leads to autoimmune disease, such as type 1 diabetes.
Unlike T-cells and B-cells, macrophages use phagocytosis and digestion as their principal functions. Macrophages are directed to the site of infection by chemical mediators, such as chemokines and cytokines. These mediators react with surface proteins on macrophages and induce intracellular changes, driving the macrophages to the site of infection. Which of the following is likely true of this form of cell signaling?
I. It is mediated by an intracellular second messenger
II. It exclusively mediates changes in gene expression in the macrophage
III. It drives intracellular changes to occur over several days or weeks
IV. It is an example of autocrine signaling
The signaling system with chemokines and cytokines is an example of a paracrine signaling process, where nearby cells communicate with each other, rather than autocrine signaling, where a single cell releases a signal to itself. The attraction of macrophages to the site of infection must occur quickly, much faster than several days or weeks. It also must use a second messenger, which will likely have immediate cytosolic effects as well as effects on genetic expression, because it acts through a surface receptor on the macrophage.
The signaling system with chemokines and cytokines is an example of a paracrine signaling process, where nearby cells communicate with each other, rather than autocrine signaling, where a single cell releases a signal to itself. The attraction of macrophages to the site of infection must occur quickly, much faster than several days or weeks. It also must use a second messenger, which will likely have immediate cytosolic effects as well as effects on genetic expression, because it acts through a surface receptor on the macrophage.
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Listed below are events that occur during a signal transduction pathway.
I. The plasma membrane receptor interacts with an effector protein
II. Second messenger molecules are released
III. Ligand binds to the plasma membrane receptor
Which of the following lists these events in the correct order?
Listed below are events that occur during a signal transduction pathway.
I. The plasma membrane receptor interacts with an effector protein
II. Second messenger molecules are released
III. Ligand binds to the plasma membrane receptor
Which of the following lists these events in the correct order?
Signal transduction involves transmission of signals between cells. In a normal signal transduction pathway, a ligand (such as a hormone and neurotransmitter) binds to a cell membrane receptor on the extracellular side. Ligand binding initiates a response on the intracellular side. One such response includes the binding of the intracellular side to an effector protein. Binding of the receptor to an effector protein releases second messenger molecules that propagate and amplify the signal, often influencing transcription factors and gene expression.
There are several signal transduction pathways, but the ligand always binds to the extracellular side of the receptor and initiates a response on the intracellular side of the receptor.
Signal transduction involves transmission of signals between cells. In a normal signal transduction pathway, a ligand (such as a hormone and neurotransmitter) binds to a cell membrane receptor on the extracellular side. Ligand binding initiates a response on the intracellular side. One such response includes the binding of the intracellular side to an effector protein. Binding of the receptor to an effector protein releases second messenger molecules that propagate and amplify the signal, often influencing transcription factors and gene expression.
There are several signal transduction pathways, but the ligand always binds to the extracellular side of the receptor and initiates a response on the intracellular side of the receptor.
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The force generated by a muscle when it contracts involves muscle proteins within muscle cells, namely actin and myosin. Beginning with the arrival of an action potential from the motor neuron’s axon, muscles generate force through a cascade of electrical and biochemical events. The release of acetylcholine at the presynaptic membrane into the synaptic cleft is caused by the action potential which opens calcium 
channels. Temporary binding of neurotransmitter at the postsynaptic membrane with the muscle’s acetylcholine receptors leads to depolarization of the postsynaptic membrane and opening of calcium channels. Twisting of tropomyosin to expose myosin attachment sites on actin is the result of calcium released from the sarcoplasmic reticulum and binding to troponin molecules. two strands of protein, myosin and actin, attach to each other by forming a cross-bridge which allows them to slide relative to each other to shorten the muscle and generate force. When depolarization ends, 
is pumped back into the sarcoplasmic reticulum and actin- myosin cross-bridges can no longer form resulting in relaxation.
When a motor neuron is electrically stimulated with a single impulse, a muscle innervated by that neuron produces a force called a twitch. Whereas the impulse might be 1 to 3msec in duration, the twitch is 10 to 100msec long. This is because it takes a long time for the 
to be pumped back into the sarcoplasmic reticulum. When the rate of impulses is low, the twitches have time to relax (Figure 1A). When the rate of simulation is high, the twitches fuse and the force in the muscle sums (Figures 1B and 1C). Maximal tension in the muscle, a condition known as tetanus (Figure 1D), is generated when the frequency of action potential is raised to the point when all cross- bridge binding sites are continuously activated and force output no longer shows any ripples.
Figure 1
Myasthenia gravis (MG) is a disease in which the number of acetylcholine receptors at the postsynaptic neuromuscular junctions becomes greatly reduced. What is the expected difference between contraction of the muscle of the MG patient and that of a healthy person in response to stimulation by a neuron?
The force generated by a muscle when it contracts involves muscle proteins within muscle cells, namely actin and myosin. Beginning with the arrival of an action potential from the motor neuron’s axon, muscles generate force through a cascade of electrical and biochemical events. The release of acetylcholine at the presynaptic membrane into the synaptic cleft is caused by the action potential which opens calcium
When a motor neuron is electrically stimulated with a single impulse, a muscle innervated by that neuron produces a force called a twitch. Whereas the impulse might be 1 to 3msec in duration, the twitch is 10 to 100msec long. This is because it takes a long time for the
Figure 1
Myasthenia gravis (MG) is a disease in which the number of acetylcholine receptors at the postsynaptic neuromuscular junctions becomes greatly reduced. What is the expected difference between contraction of the muscle of the MG patient and that of a healthy person in response to stimulation by a neuron?
This question asks how the response of muscle of an MG patient would differ from the response of muscle of a healthy person to stimulation by a neuron. This is a question that can stand alone from the passage; no information or data from the passage is required to answer the question.
When acetylcholine binds its receptor on a muscle cell it produces a depolarization wave that opens 
channels in the plasma membrane and sarcoplasmic reticulum. As a result, 
flows out into the sarcoplasm where it stimulates the interaction of actin and myosin and the sliding of the filaments. Since a patient with myasthenia gravis will have a reduced number of functional acetylcholine receptors, the depolarization signal will be smaller, less 
will be released and fewer actin-myosin cross bridges will form. This sequence of events will result in the weaker contraction in the muscle of the myasthenia gravis patient. The number of troponin molecules bound to tropomyosin does not change during contraction. Troponin is bound to tropomyosin when the muscle is at rest. When 
is released from the sarcoplasmic reticulum, it binds to troponin and causes it to twist the tropomyosin enough to expose the actin myosin binding sites. Since troponin is bound to tropomyosin at rest and during contraction, there shouldn’t be any difference in the number of troponin-tropomyosin interactions in patients with myasthenia gravis as compared with normal individuals.
This question asks how the response of muscle of an MG patient would differ from the response of muscle of a healthy person to stimulation by a neuron. This is a question that can stand alone from the passage; no information or data from the passage is required to answer the question.
When acetylcholine binds its receptor on a muscle cell it produces a depolarization wave that opens
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Which organelle is primarily responsible for ATP production in eukaryotic cells?
Which organelle is primarily responsible for ATP production in eukaryotic cells?
Eukaryotic cells contain mitochondria. The inner membrane of the mitochondrion houses ATP synthase proteins, which generate molecular energy via oxidative phosphorylation. This is the primary source of cellular energy in the form of ATP.
Chloroplasts are another eukaryotic organelle involved in energy production. However, the primary function of the chloroplast is to use light energy to generate glucose from carbon dioxide. This glucose is then metabolized via cellular respiration, utilizing the mitochondria for the majority of ATP synthesis.
Eukaryotic cells contain mitochondria. The inner membrane of the mitochondrion houses ATP synthase proteins, which generate molecular energy via oxidative phosphorylation. This is the primary source of cellular energy in the form of ATP.
Chloroplasts are another eukaryotic organelle involved in energy production. However, the primary function of the chloroplast is to use light energy to generate glucose from carbon dioxide. This glucose is then metabolized via cellular respiration, utilizing the mitochondria for the majority of ATP synthesis.
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