Question

What is meant by cell cycle? Discuss its various stages.

Answer 1

A cell is the fundamental building block of a life. Cells having a membrane bound nucleus are called eukaryotic cells whereas those lacking a membrane around the nuclear material are called prokaryotic cells.

Complete answer:
The process in which a cell replicates its genetic material and important organelles and then divides into two identical daughter cells is called a cell cycle. Prevost and Dumas in 1824 while studying the cleavage of a frog zygote first observed the cell cycle. A series of events can be observed in a cell cycle. A typical cell cycle has two main phases – Interphase and Mitotic phase.
It starts with the first phase, i.e., Interphase. It is the resting phase and continues for the longest duration in a cell cycle. During this phase a cell gears up for cell division. It undergoes cell growth and DNA replication. The interphase includes three phases viz., G1 phase, S phase and G2 phase. Mitosis takes place after the interphase. In the G1 phase, the cell increases in size and the cellular contents get duplicated. In the S phase or synthesis phase, the replication of DNA takes place. The synthesis occurs without altering the number of chromosomes. In G2­ phase, the cell continues to grow and the genetic material gets organized and condensed. The M phase or the mitotic phase, marks the end of interphase. The mitotic phase starts with Prophase, Metaphase, Anaphase, and finally the Telophase. During mitotic cell division, first nuclear division (karyokinesis) and then cytoplasmic division (cytokinesis) occurs. After the physical separation of cytoplasmic contents two daughter cells are formed.

Note:
The duration of a cell cycle varies from organism to organism and the type of cell. Human cells being eukaryotic cells take approximately 24 hours to complete one cycle of growth and division. In culture, a mammalian intestinal cell may complete a cell cycle within 10 hours.