Molecular Cell Biology - Problem Drill 22: The Mechanics of Cell Division

Transcription

1 Molecular Cell Biology - Problem Drill 22: The Mechanics of Cell Division Question No. 1 of Which of the following statements about mitosis is correct? Question #1 (A) Mitosis involves the dividing of the cytoplasm and plasma membrane and occurs after the successful replication of the cell s DNA. (B) Mitosis involves the dividing of the nucleus and occurs after the successful replication of the cell s DNA. (C) Mitosis can be divided into 4 distinct events: (1) Prophase, (2) Prometaphase, (3) Metaphase, (4) Anaphase. (D) Mitosis can be divided into 4 distinct events: (1) Prometaphase, (3) Metaphase, (4) Anaphase and (5) Telophase. Mitosis involves the dividing of the nucleus and occurs after the successful replication of the cell s DNA. B. Correct! Mitosis involves the dividing of the nucleus and occurs after the successful replication of the cell s DNA. Mitosis can be divided into 5 distinct events: (1) Prophase, (2) Prometaphase, (3) Metaphase, (4) Anaphase and (5) Telophase. Mitosis can be divided into 5 distinct events: (1) Prophase, (2) Prometaphase, (3) Metaphase, (4) Anaphase and (5) Telophase. Mitosis involves the dividing of the nucleus and 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. Mitosis can be divided into 5 distinct events: (1) Prophase, (2) Prometaphase, (3) Metaphase, (4) Anaphase and (5) Telophase.

2 Question No. 2 of Which statement below is true about prophase? Question #2 (A) As prophase begins a single microtubule forms at the mitotic spindle. Microtubule-associated proteins and motor proteins facilitate these events. (B) As prophase begins many small microtubules form at the center of the cell. Microtubule-associated proteins and motor proteins are not involved in these events. (C) During 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. (D) During prophase the normally densely packed chromatin is loosened into the chromosome. The two centrosomes (Mitotic Spindle) begin to extend microtubules, in preparation for attaching to the chromosomes. As prophase begins many small microtubules form at the mitotic spindle. Microtubule-associated proteins and motor proteins facilitate these events. As prophase begins many small microtubules form at the mitotic spindle. Microtubule-associated proteins and motor proteins facilitate these events. C. Correct! During 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. During 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. Mitosis can be divided into 5 distinct events: (1) Prophase, (2) Prometaphase, (3) Metaphase, (4) Anaphase and (5) Telophase. 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. As prophase begins, the large microtubules that exist during interphase become unstable and breakdown. Then, many small microtubules form at the mitotic spindle. Microtubule-associated proteins and motor proteins facilitate these events.

3 Question No. 3 of Which of the following statements about prometaphase is correct? Question #3 (A) Prometaphase begins with the construction of new nuclear membranes. Chromosomes attach to spindle microtubules at their kinetochore. (B) Prometaphase begins with the breakdown of the nuclear envelope. Chromosomes attach to spindle microtubules at their kinetochore. (C) The Kinetochore is made up of a single protein, to which the mitotic spindle microtubule attaches. (D) Molecular motors at the kinetochore, prevent polymerization and depolyerization of microtubules, and therefore, inhibit the movement of the individual chromatids towards the pole of the mitotic spindle. Prometaphase begins with the breakdown of the nuclear envelope. Chromosomes attach to spindle microtubules at their kinetochore. B. Correct! Prometaphase begins with the breakdown of the nuclear envelope. Chromosomes attach to spindle microtubules at their kinetochore. The Kinetochore is made up of a group of proteins, to which the mitotic spindle microtubule attaches. Molecular motors at the kinetochore, along with polymerization and depolymerization of microtubules, facilitate the movement of the individual chromatids towards the pole of the mitotic spindle. Prometaphase begins with the breakdown of the nuclear envelope. Chromosomes attach to spindle microtubules at their kinetochore. The Kinetochore is made up of a group of proteins, to which the mitotic spindle microtubule attaches. Molecular motors at the kinetochore, along with polymerisation and depolymerisation of microtubules, facilitate the movement of the individual chromatids towards the pole of the mitotic spindle.

4 Question No. 4 of Which of the following statements about metaphase is correct? Question #4 (A) During metaphase the chromosomes are aligned at the center of the cell at a region called the metaphase plate. (B) During metaphase the chromosomes are aligned at the cell periphery near the mitotic spindle. (C) Chromosomes are held in position at the metaphase plate by a single force: (1) tubulin subunits begin to be added to the microtubule at the kinetochore and removed at the spindle poles. (D) Chromosomes are held in position at the metaphase plate by a single force: (1) Kinetochores pull the chromosome towards the pole (poleward force) and, simultaneously, the astral ejection force pushes the chromosomes away from the spindle pole. A. Correct! During metaphase the chromosomes are aligned at the center of the cell at a region called the metaphase plate. During metaphase the chromosomes are aligned at the center of the cell at a region called the metaphase plate. Chromosomes are held in position at the metaphase plate by 2 opposing forces: (1) tubulin subunits begin to be added to the microtubule at the kinetochore and removed at the spindle poles and (2) Kinetochores pull the chromosome towards the pole (poleward force) and, simultaneously, the astral ejection force pushes the chromosomes away from the spindle pole. Chromosomes are held in position at the metaphase plate by 2 opposing forces: (1) tubulin subunits begin to be added to the microtubule at the kinetochore and removed at the spindle poles and (2) Kinetochores pull the chromosome towards the pole (poleward force) and, simultaneously, the astral ejection force pushes the chromosomes away from the spindle pole. Metaphase the chromosomes are aligned at the center of the cell at a region called the metaphase plate. Each of the sister chromatids (2 per chromosome) are attached to opposite poles of the mitotic spindle. The chromosomes are held in position at the metaphase plate by 2 opposing forces: (1) tubulin subunits begin to be added to the microtubule at the kinetochore and removed at the spindle poles and (2) Kinetochores pull the chromosome towards the pole (poleward force) and, simultaneously, the astral ejection force pushes the chromosomes away from the spindle pole.

5 Question No. 5 of Which of the following statements about anaphase is correct? Question #5 (A) Anaphase is triggered by the actin-promoting complex (APC). (B) During anaphase, the sister chromatids are pulled together as a chromosome, towards the spindle they are connected to. (C) Anaphase is delayed until a signal verifies to the cell that all the chromosomes are correctly lined up at the metaphase plate. (D) Anaphase is delayed until a signal verifies to the cell that all the chromosomes are correctly lined up at the mitotic spindle (periphery of the cell). Anaphase is triggered by the anaphase-promoting complex (APC). During anaphase, the sister chromatids are separated and pulled towards the spindle they are connected to. C. Correct! Anaphase is delayed until a signal verifies to the cell that all the chromosomes are correctly lined up at the metaphase plate. Anaphase is delayed until a signal verifies to the cell that all the chromosomes are correctly lined up at the metaphase plate. Anaphase is delayed until a signal verifies to the cell that all the chromosomes are correctly lined up at the metaphase plate. Anaphase is triggered by the anaphasepromoting complex (APC). The APC cleaves the M phase cyclin and activates a protein called separase, which cleaves the complex that holds the sister chromatids together. During anaphase, the sister chromatids are separated and pulled towards the spindle they are connected to. The chromatids move by 2 overlapping processes: (A) poleward movement of the chromatid due to the shortening of the kinetochore microtubules. This process depends on motor proteins at the kinetochore. (B) Separation of the poles themselves, which begins after the sister chromatids have moved some distance apart. This process depends on motor proteins at the spindle poles.

6 Question No. 6 of Which of the following statements about telophase is correct? Question #6 (A) A single nuclear envelope reassembles around both of the 2 sets of chromosomes. (B) Nuclear membrane fragments associate with the chromosomes and form the contractile ring. (C) During telophase the sister chromatids arrive at the spindles and decondense; the microtubules disassemble. (D) During telophase each intact chromosome arrives at the spindle and decondenses; the microtubules disassemble. A nuclear envelope reassembles around each of the 2 separated sets of chromosomes. Nuclear membrane fragments associate with the chromosomes and re-form the nuclear envelope. C. Correct! During telophase the sister chromatids arrive at the spindles and decondense; the microtubules disassemble. During telophase the sister chromatids arrive at the spindles and decondense; the microtubules disassemble. Telophase the sister chromatids arrive at the spindles and decondense; the microtubules disassemble. A nuclear envelope reassembles around each of the 2 separated sets of chromosomes. Nuclear membrane fragments associate with the chromosomes and re-form the nuclear envelope. Nuclear lamin proteins are dephosphorylated and re-form the nuclear lamina. The cell is now ready for cytokineses (division of the cytoplasm).

7 Question No. 7 of Which of the following statements about cytokinesis is correct? Question #7 (A) Cytokinesis is the process whereby the nucleus of a cell is divided to produce 2 daughter cells. (B) Cytokinesis is the process whereby the cytoplasm of a cell is divided to produce 2 daughter cells. (C) Eventually, as cytokinesis progresses, the cleavage furrow deepens until the nuclear membrane and its contents are divided. (D) Eventually, as cytokinesis progresses, the cleavage furrow disappears and the two daughter cells are formed into 1 cell. Cytokinesis is the process whereby the cytoplasm of a cell is divided to produce 2 daughter cells. B. Correct! Cytokinesis is the process whereby the cytoplasm of a cell is divided to produce 2 daughter cells. Eventually, as cytokinesis progresses, the cleavage furrow deepens until the plasma membrane and its contents are divided. Eventually, as cytokinesis progresses, the cleavage furrow deepens until the plasma membrane and its contents are divided. During telophase, a groove can be seen forming near the metaphase plate, called the cleavage furrow. The mitotic spindle specifies the location of the cleavage furrow. Eventually, as cytokinesis progresses, the cleavage furrow deepens until the plasma membrane and its contents are divided.

8 Question No. 8 of Which of the following statements about the contractile ring is correct? Question #8 (A) Within the cleavage furrow are a group of proteins known as the contractile ring. (B) Within the cleavage furrow a single protein makes up the contractile ring. (C) The contractile ring is located outside the cell near the plasma membrane and eventually contracts to completely cut the cell into 2 daughter cells. (D) The contractile ring includes a single protein called myosin. A. Correct! Within the cleavage furrow are a group of proteins known as the contractile ring. Within the cleavage furrow are a group of proteins known as the contractile ring. The contractile ring is located just beneath the plasma membrane and eventually contracts to completely cut the cell into 2 daughter cells. The contractile ring includes actin filaments and myosin 2 filaments. Within the cleavage furrow are a group of proteins known as the contractile ring. The contractile ring includes actin filaments and myosin 2 filaments. The contractile ring is located just beneath the plasma membrane and eventually contracts to completely cut the cell into 2 daughter cells.

9 Question No. 9 of Which of the following statements about actin and myosin 2 proteins is correct? Question #9 (A) Actin and Myosin 2 generate the necessary forces for the contractile ring to constrict and cleave the cell into 2 daughter cells. (B) Actin is a motor protein and it generates the necessary forces for the contractile ring to constrict and cleave the cell into 2 daughter cells. (C) Myosin 2 is activated when a potassium-dependent kinase phosphorylates it. (D) Myosin 2 is activated when a calcium-independent kinase phosphorylates it. A. Correct! Actin and Myosin 2 generate the necessary forces for the contractile ring to constrict and cleave the cell into 2 daughter cells. Actin and Myosin 2 generate the necessary forces for the contractile ring to constrict and cleave the cell into 2 daughter cells. Myosin 2 is activated when a calcium-dependent kinase phosphorylates it. Myosin 2 is activated when a calcium-dependent kinase phosphorylates it. Actin and Myosin 2 generate the necessary forces for the contractile ring to constrict and cleave the cell into 2 daughter cells. Myosin 2 is a motor protein and it, along with the overlapping actin filaments, contracts the ring. Myosin 2 is activated when a calcium-dependent kinase phosphorylates it. Actin filaments are moved in a stepwise fashion as the myosin 2 undergoes a conformational change, moving the filament forward.

10 Question No. 10 of Which of the following statements about when mitosis occurs without cytokinesis is correct? Question #10 (A) In most cells of the human body, there are many cytokinesis events for each mitosis. (B) In most cells of the human body, there is one cytokinesis for each mitosis. (C) There are many examples of cells that normally have multiple rounds of mitosis without cytokinesis. An example of this is the trophoblast from early embryonic development. (D) There is a single example of cells that normally have multiple rounds of mitosis without cytokinesis. An example of this is the T-Cell. In most cells of the human body, there is one cytokinesis for each mitosis. B. Correct! In most cells of the human body, there is one cytokinesis for each mitosis. There are a few examples of cells that normally have multiple rounds of mitosis without cytokinesis. An example of this is the trophoblast from early embryonic development. There are a few examples of cells that normally have multiple rounds of mitosis without cytokinesis. An example of this is the trophoblast from early embryonic development. In most cells of the human body, there is one cytokinesis for each mitosis. There are a few examples of cells that normally have multiple rounds of mitosis without cytokinesis. An example of this is the trophoblast from early embryonic development. Trophoblasts are cells that are part of the blastocyst. The blastocyst implants into the wall of the uterus and develops during the first stage of pregnancy.