CELL DIVISION
THE CELL CYCLE
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Cyclins are carbohydrates that regulate DNA replication during the mitosis phase of the cell cycle.
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Cyclins are glycoproteins that repair DNA in the beginning of cell cycle.
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Cyclins are proteins that regulate when and how often a cell divides.
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Detailed explanation-1: -Cyclin is a family of proteins that controls the progression of a cell through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes or group of enzymes required for synthesis of cell cycle.
Detailed explanation-2: -Cyclins are the regulatory subunits of holoenzyme CDK complexes that control progression through cell-cycle checkpoints by phosphorylating and inactivating target substrates. The cyclins associate with different CDKs to provide specificity of function at different times during the cell cycle (see Fig. 9-2).
Detailed explanation-3: -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-4: -When cyclins are synthesized, they act as an activating protein and bind to Cdks forming a cyclin-Cdk complex. This complex then acts as a signal to the cell to pass to the next cell cycle phase. Eventually, the cyclin degrades, deactivating the Cdk, thus signaling exit from a particular phase.
Detailed explanation-5: -Phosphorylation by CDK-2-cyclin E complex prevents this inhibition and so progression from G1 to S phase can continue. Overall, cyclins are responsible for the progression of the cell cycle, ensuring that the important stages of each phase are carried out before the cell progresses into the next phase.