Tag: Cell cycle

Post-translational modifications are essential regulators of cell-cycle progression. Learn how phosphorylation, ubiquitination, acetylation, SUMOylation, methylation, and other PTMs control CDKs, cyclins, checkpoints, DNA replication, mitosis, and protein degradation.

Timely protein degradation is essential for orderly cell-cycle progression. Explore key cell-cycle regulators, their degradation mechanisms, and how their turnover controls G1/S transition, mitosis, chromosome segregation and mitotic exit.

Cdc25 phosphatases activate CDKs to drive both the G1–S and G2–M transitions. By removing inhibitory phosphates from CDK1 and CDK2, Cdc25 triggers DNA replication and mitotic entry. Checkpoint kinases such as Chk1 inhibit Cdc25 during DNA damage, while Cdc25 overexpression promotes genomic instability and contributes to tumour progression.

pRb is a major tumour‑suppressor that governs the G1–S transition by restraining E2F transcription factors and maintaining a repressive chromatin state. When pRb becomes hyperphosphorylated, cells commit to DNA replication. Loss of pRb function leads to uncontrolled proliferation, replication stress and genomic instability, making it a key player in cancer development.

Cdh1 is a major activator of the APC/C complex, responsible for mitotic exit, G1 maintenance and replication licensing. By degrading Cyclin B, Aurora A, Plk1 and Geminin, Cdh1 prevents premature S‑phase entry and maintains genomic stability. Its dysregulation contributes to replication stress, chromosomal instability and cancer development.

Endoreduplication is a specialised cell‑cycle variant in which cells repeatedly replicate their DNA without mitosis, producing polyploid nuclei. Driven by Cyclin E, CDK2, APC/C–Cdh1 and E2F7/8, this process enhances cell size, biosynthetic capacity and stress tolerance in plants, insects and mammalian tissues.

Asymmetric cell division produces daughter cells with different sizes, molecular compositions or developmental fates. Guided by polarity complexes, spindle orientation and unequal segregation of determinants such as Numb and Prospero, this process maintains stem‑cell pools, drives tissue development and prevents uncontrolled proliferation. Its disruption contributes to degenerative disease and cancer.

Cell‑cycle checkpoints act as surveillance systems that monitor DNA integrity, replication completeness and spindle attachment. The G1, G2 and spindle checkpoints prevent cells with damage or misaligned chromosomes from dividing, ensuring accurate genome transmission and protecting against genomic instability and cancer.

Cell‑cycle genes coordinate the progression of G1, S, G2, and M phases through cyclins, CDKs, checkpoints, and replication machinery. Their precise regulation ensures accurate DNA duplication, faithful chromosome segregation, and controlled cell proliferation. Understanding these genes is essential for explaining genomic stability and the molecular basis of cancer.

The G1/S transition is the critical checkpoint where a cell commits to DNA replication. It integrates cyclin–CDK activity, Rb phosphorylation, and E2F activation to ensure accurate S‑phase entry. Proper regulation protects genomic stability and prevents uncontrolled proliferation.

Embryonic cleavage cycles transform a single‑celled zygote into a multicellular embryo through rapid, synchronous divisions. This article explains cleavage patterns, maternal control, and the mid‑blastula transition.

Binary fission is a rapid and efficient form of asexual reproduction in prokaryotes. It involves DNA replication, chromosome segregation, and septum formation, resulting in two identical daughter cells.

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The S phase is the period of the cell cycle in which DNA is replicated, producing identical copies of the genome for distribution to daughter cells. It is tightly regulated to maintain accuracy and prevent genomic instability.

The G₂ phase is the period after DNA replication during which the cell checks for errors, repairs damage, and prepares for mitosis. It is essential for accurate chromosome segregation and genomic stability.