Passage
Trypanosoma brucei is a eukaryotic parasite that causes sleeping sickness in Sub-Saharan Africa. The cell cycle of T. brucei differs from that of higher eukaryotes. For example, the chromatin does not condense during mitosis, and the nuclear envelope remains intact. In addition, the nucleus divides before cell division, and the cell divides along the longitudinal axis (Figure 1) .
Figure 1 Mitosis in T. bruceiA culture of T. brucei was arrested in S phase of the cell cycle by overnight incubation with the reversible inhibitor hydroxyurea. The cells were then washed, and their progression through the cell cycle was monitored by flow cytometry and microscopy. A subset of the culture was first exposed to the drug VX-680, which arrests cells upon completion of metaphase. The results are shown in Figure 2.
Figure 2 Percentages of a population of T. brucei cells in each phase of the cell cycle, measured at different time points in the (A) absence and (B) presence of VX-680
Adapted from Li Z, Umeyama T, Wang CC. The Aurora Kinase in Trypanosoma brucei plays distinctive roles in metaphase-anaphase transition and cytokinetic initiation. PLoS Pathog. 2009;5(9) :e1000575.
-Based on Figure 2, in the absence of VX-680, how long does it take T. brucei cells released from S phase at 0 hours to complete one full cell cycle?

Question

Passage
Trypanosoma brucei is a eukaryotic parasite that causes sleeping sickness in Sub-Saharan Africa. The cell cycle of T. brucei differs from that of higher eukaryotes. For example, the chromatin does not condense during mitosis, and the nuclear envelope remains intact. In addition, the nucleus divides before cell division, and the cell divides along the longitudinal axis (Figure 1) .

Figure 1 Mitosis in T. bruceiA culture of T. brucei was arrested in S phase of the cell cycle by overnight incubation with the reversible inhibitor hydroxyurea. The cells were then washed, and their progression through the cell cycle was monitored by flow cytometry and microscopy. A subset of the culture was first exposed to the drug VX-680, which arrests cells upon completion of metaphase. The results are shown in Figure 2.

Figure 2 Percentages of a population of T. brucei cells in each phase of the cell cycle, measured at different time points in the (A) absence and (B) presence of VX-680
Adapted from Li Z, Umeyama T, Wang CC. The Aurora Kinase in Trypanosoma brucei plays distinctive roles in metaphase-anaphase transition and cytokinetic initiation. PLoS Pathog. 2009;5(9) :e1000575.
-Based on Figure 2, in the absence of VX-680, how long does it take T. brucei cells released from S phase at 0 hours to complete one full cell cycle?

Quizplus · Accepted Answer

11ecba2d_101b_6c65_a3bf_9fb524dbe182_MD0008_00 The cell cycle consists of a set of distinct phases (G₁, S, G₂, and M phase) through which a cell progresses as it grows and divides. To complete one cycle, a cell starting in any phase must pass through all other phases and return to the phase in which it began. For example, a cell in G₁ must pass through S, G₂, and M, then return to G₁ to complete the cycle. Figure 2A shows the percentages of a population of T. brucei cells in each phase of the cell cycle in the absence of VX-680. The majority of T. brucei cells were in S phase when the experiment began, and they returned to S phase 8 hours later after passing through G₂, M, and G₁. Therefore, the graph shows that it takes 8 hours for T. brucei cells to complete one full cell cycle in the absence of VX-680. (Choice A) At 4 hours after the experiment began, the majority of cells were in M phase. Because T. brucei cells started in S phase, they need to return to S phase to complete a full cycle. (Choice B) At 6 hours, the majority of cells were in G₁ phase. They need to return to S phase to complete a full cycle. (Choice D) The length of the experiment was 10 hours, but T. brucei completed the cell cycle in 8 hours. Educational objective: To complete one full cell cycle, a cell starting in any given phase must pass through all the other phases and return to the initial phase.

Passage Trypanosoma Brucei Is a Eukaryotic Parasite That Causes Sleeping Sickness