REPRODUCTION
EMBRYONIC DEVELOPMENT
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Ensure that all chromosomes have lined up in the center of the cell before cell division
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Ensure that spindle fibers have attached to all centromeres before cell division
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Ensure that DNA has been replicated before cell division
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All of these
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Detailed explanation-1: -Cyclins regulate the activity of their Cdk partners and also modulate their substrate specificity. More than 20 Cdk-related proteins and more than 11 cyclins have been identified in more complex eukaryotes, which has led to the concept that different cell cycle events are regulated by distinct cyclin-Cdk complexes.
Detailed explanation-2: -The internal regulators are proteins inside of the cell while external regulators are proteins outside of the cell. Internal regulators will determine if the internal state of the cell is ready for cell division or not. If it is, then it allows division to proceed. If it isn’t, then it blocks cell division.
Detailed explanation-3: -Internal regulators of the cell cycle consist of two formal, well-defined types: positive regulator molecules such as cyclins and cyclin-dependent kinases and negative regulator molecules such as Rb, p53 and p21.
Detailed explanation-4: -The levels of the four cyclin proteins fluctuate throughout the cell cycle in a predictable pattern ([link]). Increases in the concentration of cyclin proteins are triggered by both external and internal signals.