Biology-Cell Cycle
Example Question #1342 : Biology 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? A. 100 B. 50 C. 25 D. 200
A 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.
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? A. G0 phase B. M phase C. S phase D. G1 phase E. G2 phase
B Cell division occurs in M phase. Thus, if the cells are experiencing uncontrolled growth, they are probably remaining in M phase abnormally long.
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? A. cyclin-dependent kinase B. cyclin-dependent kinase inhibitor C. p53 D. DNA polymerase
B 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.
Example Question #3 : Cellular Processes And Functions 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? A. M B. G1 C. S D. G2 E. G0
B 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.
During which of the following portions of the cell cycle are mRNA and proteins mainly produced? A. G2 B. S C. G1 D. M
C 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.
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? A. G1 and G2 phase both involve cell growth B. G0 and G1 phase both involve increasing the amount of genetic material C. more than one of these D. G0 phase involves no cell growth
C 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.
Example Question #1341 : Biology 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? A. S phase B. G1 phase C. more than one of these D. G2 phase
C 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.
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 A. I and III B. II only C. I, II, and III D. I and II
C 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.
Which of the following factors might cause cell cycle growth arrest? A. Failure of the chromosomes to line up on the equatorial plate during mitosis B. DNA damage C. lack of appropriate growth factors D. all of these answers
D 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.
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? A. pH3 B. Each method will detect the same number of proliferating cells C. MK167 D. BrdU
D 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.
During which of the following portions of the cell cycle is DNA polymerase most active? A. G1 B. G0 C. M D. S
D 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.
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? A. G2 B. M C. S D. G0 E. G1
D Neural Cells are arrested in the Go phase to prevent growth. This arresting phase prevents abnormal growth and cancer cells development. G1 and G2 involve cell growth and duplication of organelles. S phase is the time in which DNA is duplicated, and M phase stands for mitosis, or meiosis, in which the nucleus divides.
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? A. G1 phase B. Chromosomes are visible during all portions of the cell cycle C. S phase D. G2 phase E. M phase
E 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.
Example Question #1 : Cell Cycle Which process does not occur in the pachytene phase of prophase I? A. none of the other answers B. crossover takes place C. synapsis is completed D. synapsed chromosomes bunch up and become thick E. tetrads move towards the midline
E 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 eukaryotic cell cycle, what is the purpose of the G2/M checkpoint? A. To allow for formation of the spindle fibers B. To ensure that all chromosomes are aligned properly for cell division C. To ensure that the cell is ready to divide D. To ensure that the cell is large enough for cell division E. To ensure that DNA hasn't been damaged during S phase
E 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.
