Cyclin-dependent kinases (CDKs) belong to a protein serine/threonine kinases whose activity depends on association with a noncatalytic regulatory subunit called a cyclin. Cyclin-dependent kinases inhibitors are vital for progression through the cell cycle and proliferation.

1. Cyclin-dependent kinase
Overview
Cyclin-dependent kinases (CDKs) belong to a protein serine/threonine kinases whose activity
depends on association with a noncatalytic regulatory subunit called a cyclin. Cyclin-dependent
kinases inhibitors are vital for progression through the cell cycle and proliferation. The genes that
encode CDKs were initially identified in screens for conditional mutants of Saccharomyces
cerevisiae which reversibly arrested at characteristic points in the cell cycle upon transfer to the
restrictive conditions. Cyclins were initially named for their periodic accumulation and
degradation (cycling) through the early cell cycles of fertilized sea urchin eggs. This research
identified a ubiquitous cell cycle engine responsible for coordinating cell growth, DNA replication,
and mitosis in the orderly fashion required to ensure the viability of progeny cells.
How Do Cyclin-dependent kinases regulate Cell Cycle?
All eukaryotes have a various cyclins, each of which acts during a specific stage of the cell cycle.
All cyclins are given names according to the stage at which they assemble with Cyclin-dependent
kinases. The classes of cyclins involves G1-phase cyclins, G1/S-phase cyclins, S-phase cyclins,
and M-phase cyclins. M-phase cyclins make M-CDK complexes and lead the entry of cell into
mitosis; G1 cyclins form G1-CDK complexes and drive the progress of cells through the G1 phase.
All Cyclin-dependent kinases present in equal amounts throughout the entire cell cycle. The cyclin
produce and malfunction change by stage with cell cycle advancement dependent on the new
cyclin molecules synthesis. The cells produce G1- and G1/S-cyclins at different times during the
G1 phase, and they produce M-cyclin molecules during the G2 phase. Cyclin degradation is
equally essential for advancement through the cell cycle. Specific enzymes fail cyclins at specific
times in the cell cycle. When cyclin levels go low, the corresponding CDKs become inoperative.
Cell cycle arrest can happen if cyclins fail to degrade.
Which Proteins Do Cyclin-dependent kinases transform?
Each of the cyclin-CDK complexes in a cell alters a particular group of protein substrates. Proper
phosphorylation of these substrates ought to happen at specific times in order for the cell cycle to
continue. Because cyclin-CDK complexes recognize multiple substrates, they can correlate the
various events that happen during each phase of the cell cycle. For example, at the start of S phase,
S-CDK catalyzes the phosphorylation of the proteins that start DNA replication by admitting DNA
replication complexes to make. During mitosis, M-CDKs phosphorylate a broad range of proteins.
These involve condensin proteins that are vital for the substantial condensation of mitotic
chromosomes, and lamin proteins, which make a stabilizing network under the nuclear membrane,
which dismantles during mitosis. M-CDKs also control the assembly of the mitotic spindle by
phosphorylating proteins that regulate microtubule behaviour. The effect of these coordinated
phosphorylation reactions is the final division of chromosomes during mitosis.

2. Hence, the life cycle of a cell is a prudently controlled series of events arranged by a suite of
enzymes and other proteins. The main controlling components of cell cycle regulation are cyclins
and CDKs. Depending on the occurrence and action of these proteins, the cell cycle can be fast or
sluggish and it may even stop altogether.