A. Incorrect! The Cell Cycle contains 4 distinct phases: (1) G 1, (2) S Phase, (3) G 2 and (4) M Phase.

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1 Molecular Cell Biology - Problem Drill 21: Cell Cycle and Cell Death Question No. 1 of Which of the following statements about the cell cycle is correct? Question #1 (A) The Cell Cycle contains 3 distinct phases: (1) S Phase, (2) G 2 and (3) M Phase. (B) The Cell Cycle contains 4 distinct phases: (1) G 1, (2) S Phase, (3) G 2 and (4) M Phase. (C) Cell-Cycle Control System uses lipids, which utilize key checkpoints to control cell-cycle progression. (D) Cell-Cycle Control System uses carbohydrates, which utilize key checkpoints to control cell-cycle progression. The Cell Cycle contains 4 distinct phases: (1) G 1, (2) S Phase, (3) G 2 and (4) M Phase. B. Correct! The Cell Cycle contains 4 distinct phases: (1) G 1, (2) S Phase, (3) G 2 and (4) M Phase. Cell-Cycle Control System uses a regulatory set of proteins, which utilize key checkpoints to control cell-cycle progression. Cell-Cycle Control System uses a regulatory set of proteins, which utilize key checkpoints to control cell-cycle progression. The cell cycle is required for cell division and it is highly regulated to ensure accurate cell replication. The Cell Cycle: Facilitates Cell Reproduction: Through Duplication of Cell Contents and Organelles. Contains 4 Distinct Phases: (1) G 1, (2) S Phase, (3) G 2 and (4) M Phase. Cell-Cycle Control System: A Regulatory set of Proteins which Utilize Key Checkpoints To control Cell-Cycle Progression.

2 Question No. 2 of Gap 1(G 1 ) Phase. Question #2 (A) A cell enters G 0 when the signal to divide is turned on; some cells exist in a G 0 state for days, weeks or years. (B) G 1 is when the cell monitors its environment and position. (C) The duration of the G 1 phase is from the completion of mitosis to the beginning of DNA replication during S phase, also known as interphase. (D) The duration of the G 1 phase is from the completion of S Phase to the beginning of Mitosis also known as interphase. A cell enters G 0 when the signal to divide is turned off; some cells exist in a G 0 state for days, weeks or years. G 1 is when the cell monitors its environment and size. During this time the cell grows. C. Correct! The duration of the G 1 phase is from the completion of mitosis to the beginning of DNA replication during S phase, also known as interphase. The duration of the G 1 phase is from the completion of mitosis to the beginning of DNA replication during S phase, also known as interphase. G 1 : The duration of the G 1 phase is from the completion of mitosis to the beginning of DNA replication during S phase, also known as interphase. Within the G 1 phase is a resting state known as G 0. A cell enters G 0 when the signal to divide is turned off; some cells exist in a G 0 state for days, weeks or years. In cells that are actively cycling through the cell cycle, G 1 is when the cell monitors its environment and size. During this time the cell grows.

3 Question No. 3 of Which of the following statements about S Phase is correct? Question #3 (A) In order for a cell to divide successfully, it must copy its DNA to be able to supply 2 daughter cells. During S phase, a cell must copy most of its DNA. (B) In order for a cell to divide successfully, it must copy its entire DNA to be able to supply 2 daughter cells. During S phase, (synthesis phase) a cell must copy its chromosome and the entire DNA it contains. (C) S phase lasts approximately 8 days in normal eukaryotic cells. (D) During S Phase, DNA must be made severed for replication and returned to its resting state. In order for a cell to divide successfully, it must copy its entire DNA to be able to supply 2 daughter cells. During S phase, (synthesis phase) a cell must copy its chromosome and the entire DNA it contains. B. Correct! In order for a cell to divide successfully, it must copy its entire DNA to be able to supply 2 daughter cells. During S phase, (synthesis phase) a cell must copy its chromosome and the entire DNA it contains. S phase lasts approximately 8 hours in normal eukaryotic cells. During this time, DNA must be made accessible for replication and returned to its resting state. In order for a cell to divide successfully, it must copy its entire DNA to be able to supply 2 daughter cells. During S phase, (synthesis phase) a cell must copy its chromosome and the entire DNA it contains. S phase lasts approximately 8 hours in normal eukaryotic cells. During this time, DNA must be made accessible for replication and returned to its resting state.

4 Question No. 4 of Which of the following statements about replication forks is correct? Question #4 (A) During DNA replication, a Replication fork is formed and this is where the existing DNA serves as a template to copy and produce a complete second set. (B) There are many replication forks initiated one after the other, they do not exist at the same time. (C) A single replication forks must complete the replication of approximately 3.5 billion nucleotides. (D) In order for DNA replication to begin, the DNA itself must be unwound and accessible. DNA polymerase proceeds the replication sites and performs this function. A. Correct! During DNA replication, a Replication fork is formed and this is where the existing DNA serves as a template to copy and produce a complete second set. There are many replication forks initiated simultaneously throughout the chromosome, to complete the replication of approximately 3.5 billion nucleotides. There are many replication forks initiated simultaneously throughout the chromosome, to complete the replication of approximately 3.5 billion nucleotides. In order for DNA replication to begin, the DNA itself must be unwound and accessible. DNA Helicase preceeds the replication sites and performs this function. During DNA replication, a Replication fork is formed and this is where the existing DNA serves as a template to copy and produce a complete second set. There are many replication forks initiated simultaneously throughout the chromosome, to complete the replication of approximately 3.5 billion nucleotides. In order for DNA replication to begin, the DNA itself must be unwound and accessible. DNA Helicase preceeds the replication sites and performs this function. RNA primers serve as the templates from which DNA polymerases can start joining pairs of nucleotides together.

5 Question No. 5 of Which of the following statements about Gap 2 (G 2 ) is correct? Question #5 (A) The G 2 phase is usually the longest phase of the cell cycle. (B) The G 2 phase is usually the longest phase of the cell cycle. The size of the cell is verified prior to the cell entering Mitosis. (C) Gap 2 (G 2 ): is the interphase between the end of S phase and beginning of Mitosis. (D) Gap 2 (G 2 ): is the interphase between the end of Mitosis and the beginning of S phase. The G 2 phase is usually the shortest phase of the cell cycle. The G 2 phase is usually the shortest phase of the cell cycle. The fidelity of the copied DNA is verified prior to the cell entering Mitosis. C. Correct! Gap 2 (G 2 ): is the interphase between the end of S phase and beginning of Mitosis. Gap 2 (G 2 ): is the interphase between the end of S phase and beginning of Mitosis. Gap 2 (G 2 ): is the interphase between the end of S phase and beginning of Mitosis. During G 2, the cell verifies the accuracy of the DNA replication that took place during S phase. The G 2 phase is usually the shortest phase of the cell cycle. The fidelity of the copied DNA is verified prior to the cell entering Mitosis.

6 Question No. 6 of Which of the following statements about mitosis is correct? Question #6 (A) Mitosis involves the dividing of the nucleus and the surrounding cell. Mitosis occurs directly after G 1 phase. (B) During mitosis, the parent DNA and copied DNA must be combined. (C) During mitosis, the parent DNA and copied DNA must be separated. (D) Following mitosis the cytosol and cell membrane are combined. Mitosis involves the dividing of the nucleus and the surrounding cell. Mitosis occurs after the successful replication of the cell s DNA. During mitosis, the parent DNA and copied DNA must be separated. C. Correct! During mitosis, the parent DNA and copied DNA must be separated. Following mitosis the cytosol and cell membrane divide during cytokinesis. Mitosis involves the dividing of the nucleus and the surrounding cell. Mitosis occurs after the successful replication of the cell s DNA. During mitosis, the parent DNA and copied DNA must be separated. Following this event, the cytosol and cell membrane divide during cytokinesis.

7 Question No. 7 of Which of the following statements about prometaphase, in mitosis is correct? Question #7 (A) Prometaphase is one of 4 events that occur during mitosis. (B) Prometaphase begins with the breakdown of the nuclear envelope. (C) Prometaphase begins with the breakdown of the mitotic spindle. (D) During prometaphase chromosomes unwind their DNA for replication. Mitosis can be divides into 5 distinct events: (1) Prophase, (2) Prometaphase, (3) Metaphase, (4) Anaphase and (5) Telophase. B. Correct! Prometaphase begins with the breakdown of the nuclear envelope. Prometaphase begins with the breakdown of the nuclear envelope. During prometaphase chromosomes attach to spindle microtubules at their kinetochore. Mitosis can be divides into 5 distinct events: (1) Prophase, (2) Prometaphase, (3) Metaphase, (4) Anaphase and (5) Telophase. (1) Prophase the normally loosely packed chromatin is condensed into the chromosome. The two centrosomes (Mitotic Spindle) begin to extend microtubules in preparation for attaching to the chromosomes. (2) Prometaphase begins with the breakdown of the nuclear envelope. Chromosomes attach to spindle microtubules at their kinetochore. (3) Metaphase the chromosomes are aligned at the center of the cell. Each of the sister chromatids (2 per chromosome) are attached to opposite poles of the mitotic spindle. (4) Anaphase the sister chromatids are separated and pulled towards the spindle they are connected to. (5) Anaphase the sister chromatids arrive at the spindles and decondense; the microtubules dissassemble. A nuclear envelope reassembles around each of the 2 separated sets of chromosomes. The cell is now ready for cytokineses (division of the cytoplasm).

8 Question No. 8 of Which of the following statements about cell cycle checkpoints is correct? Question #8 (A) During S phase, the DNA is replicated; if there were errors detected in the replicated DNA, progression through this checkpoint into G 2 would be delayed/inhibited. (B) During G 1 phase, the DNA is replicated; if there were errors detected in the replicated DNA, progression through this checkpoint into mitosis would be delayed/inhibited. (C) Prior to a cell entering S phase, both the cell size and integrity of the DNA that was replicated during G 1, are checked to ensure conditions are ready to replicate the DNA. (D) During mitosis, there is a checkpoint prior to the cell entering S phase and dividing into 2 daughter cells. A. Correct! During S phase, the DNA is replicated; if there were errors detected in the replicated DNA, progression through this checkpoint into G 2 would be delayed/inhibited. During S phase, the DNA is replicated; if there were errors detected in the replicated DNA, progression through this checkpoint into G 2 would be delayed/inhibited. Prior to a cell entering S phase, both the cell size and environment are checked to ensure conditions are ready to replicate the DNA. Damaged DNA or a cell that is too small can block the passage through this checkpoint. During mitosis, there is a checkpoint prior to the cell entering the cytokinesis phase and dividing into 2 daughter cells. The cell cycle is controlled largely by a central cell-cycle control system, made up of checkpoints. Each major step must be completed and accuracy confirmed before the cell moves into the next phase of the cell cycle. Each checkpoint involves a series of steps that take place prior to progression. During S phase, the DNA is replicated; if there were errors detected in the replicated DNA, progression through this checkpoint into G 2 would be delayed/inhibited. Prior to a cell entering S phase, both the cell size and environment are checked to ensure conditions are ready to replicate the DNA. Damaged DNA or a cell that is to small can block the passage through this checkpoint. During mitosis, there is a checkpoint prior to the cell entering the cytokinesis phase and dividing into 2 daughter cells. During this checkpoint, the chromosomes are confirmed to be aligned on the spindles, to allow proper separation into 2 separate future nuclei. Prior to a cell entering mitosis, there is a checkpoint to ensure that: the entire DNA was replicated correctly, the environment is favorable and the cell is big enough for cell division.

9 Question No. 9 of Which of the following statements about programmed cell death (apoptosis) is correct? Question #9 (A) Programmed cell death is a mechanism used by the body to remove unwanted cells as part of normal development, injury and disease. (B) A family of proteolytic enzymes called actinases mediates programmed cell death. (C) A family of lipids called caspases mediates programmed cell death. (D) Apoptotic bodies degrade and leak cellular content into the interstitial space, triggering the inflammation cascade. A. Correct! Programmed cell death is a mechanism used by the body to remove unwanted cells as part of normal development, injury and disease. A family of proteolytic enzymes called caspases mediates programmed cell death. A family of proteolytic enzymes called caspases mediates programmed cell death. Phagocytes ingest Apoptotic bodies and because the cell content did not leak into the interstitial space, there is no inflammation cascade. Programmed cell death is a mechanism used by the body to remove unwanted cells as part of normal development, injury and disease. It is the deliberate suicide of a cell that is highly regulated and quite different from necrosis, which includes inflammation and accidental cell death. A family of proteolytic enzymes called caspases mediates programmed cell death. These caspases are stored in cells as inactive pre-caspases. Once activated, these enzymes cleave target proteins in the nucleus and elsewhere in the cell, setting in motion this process. Cells can be triggered into apoptosis by signals during the cell cycle, such as improperly replicated DNA, etc. Once the cell begins this process, the cell itself shrinks in size and the chromatin condenses. Next, the nuclear envelope breaks down, in part, due to caspase cleavage of nuclear lamins. Also, the DNA itself is severed into small pieces during this step. Then, the cell breaks into small pieces called apoptotic bodies. These pieces are surrounded by plasma membrane, keeping the cellular contents inside. Finally, phagocytes ingest the apoptotic bodies and because the cell content did not leak into the interstitial space, there is no inflammation cascade.

10 Question No. 10 of Which of the following statements about the extracellular control of apoptosis is correct? Question #10 (A) Mitogens and growth factors stimulate apoptosis. (B) Mitogens and growth factors stimulate cell growth and division and, therefore, stimulate cell cycle progression; apoptosis is not activated unless there is abnormal DNA replication. (C) Transforming growth factor β (TGF- β) does not stimulate apoptosis. (D) Cells have unique death signals, or receptors, that are used to trigger apoptosis. Examples include myosin and nerve growth factor. Mitogens and growth factors stimulate cell growth and division and, therefore, stimulate cell cycle progression; apoptosis is not activated unless there is abnormal DNA replication. B. Correct! Mitogens and growth factors stimulate cell growth and division and, therefore, stimulate cell cycle progression; apoptosis is not activated unless there is abnormal DNA replication. Extracellular signals can trigger apoptosis in cells; one example is Transforming growth factor β (TGF- β). TGF- β has a role in cell proliferation, embryonic development and regulation of the immune system. Cells have unique death signals, or receptors, that are used to trigger apoptosis. Examples include Fas ligand (FasL) and Tumor necrosis factor (TNF). Mitogens and growth factors stimulate cell growth and division and, therefore, stimulate cell cycle progression; apoptosis is not activated unless there is abnormal DNA replication. Survival factors are a group of proteins used by cells. Survival factors, such as neurotrophins (Nerve Growth Factor, Brain-Derived Neurotrophic Factor), maintain cell survival in part by suppressing apoptosis. Extracellular signals can trigger apoptosis in cells; one example is Transforming growth factor β (TGFβ). TGF- β has a role in cell proliferation, embryonic development and regulation of the immune system. TGF- β binds to cell-surface receptors and activates the caspase cascade of events, leading to apoptosis. Cells have unique death signals, or receptors, that are used to trigger apoptosis. Examples include Fas ligand (FasL) and Tumor necrosis factor (TNF). When these molecules bind to their specific receptor, they initiate the death receptor-signaling pathway. An example of when FasL is utilized is when cytotoxic T-cells kill target cells. By having the FasL molecules expressed on the surface of the cells, they can induce apoptosis in the target by engaging the Fas receptor on the target cell.