NEET BIOLOGY

CELL STRUCTURES AND FUNCTION

CELL DIVISION

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
The cell cycle is regulated by
A
cyclins
B
chromosomes
C
centromeres
D
None of the above
Explanation: 

Detailed explanation-1: -The cell cycle is regulated by many cyclins and cyclin-dependent kinases (CDKs ) that are a group of serine/threonine kinases. They form complexes with cyclins to stabilize, activate, and phosphorylate CDKs in the specific phases [6, 7].

Detailed explanation-2: -The central components of the cell-cycle control system are cyclin-dependent protein kinases (Cdks), whose activity depends on association with regulatory subunits called cyclins. Oscillations in the activities of various cyclin-Cdk complexes leads to the initiation of various cell-cycle events.

Detailed explanation-3: -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-4: -Cyclin A is involved in the control of S phase and mitosis in mammalian cells. Expression of the cyclin A gene in nontransformed cells is characterized by repression of its promoter during the G1 phase of the cell cycle and its induction at S-phase entry.

Detailed explanation-5: -Regulation of cyclin levels is important for many cell cycle-related processes and can occur at several different steps of gene expression. Translational regulation of cyclins, which occurs by a variety of regulatory mechanisms, permits a prompt response to signal transduction pathways induced by environmental stimuli.

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