Variation in rates of cell division is regulated by a cell-cycle control system, which is a group of molecules, mostly proteins, within a cell that coordinates the events of the cell cycle. This control system functions through a system of checkpoints. Which assessment occurs at theG1/Scheckpoint?
A) DNA is checked for damage before entering mitosis.
B) DNA is checked for damage before cell division.
C) Correct alignment of chromosomes on the metaphase plate is checked.
D) Tension in the spindle fibers is evaluated.
E) Daughter cells are checked for replication errors.
B) DNA is checked for damage before cell division.
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Four of the five answers represent events that occurred when free oxygen (O2) became available in the atmosphere. Select the exception
a. aerobic respiration emerged. b. some organisms changed their metabolism. c. some species that could not detoxify free radicals became restricted to the low-oxygen environments that remained. d. oxygen was toxic to many species and some cells and forms of life became extinct. e. photosynthesis was no longer a common form of energy production.
The process illustrated in the accompanying figure is:
a. DNA synthesis. b. translation. c. transcription. d. a frame shift mutation. e. protein synthesis.
According to bottom-up and top-down control models of community organization, which of the following expressions would imply that an increase in the size of a carnivore (C) population would negatively impact its prey (P) population, but not vice versa?
A) P ? C B) P ? C C) C ? P D) P ? C ? P E) C ? P ?
In order to reuse an enzyme after the conclusion of an enzyme catalyzed reaction, what must occur?
A. the enzyme has to be resynthesized B. the enzyme has to separate itself from the product C. changes into an active form D. the enzyme has to decrease entropy