Every human is composed of roughly 37 trillion microscopic cells, each born from an existing cell. The series of events that leads from one cell to the next is called the cell cycle. The details differ between organisms that lack a nucleus (bacteria) and those that possess one (eukaryotes). Below is a clear, step‑by‑step guide to both pathways.
Bacteria use binary fission, while eukaryotic cells progress through interphase, mitosis, and cytokinesis.
In bacteria, the chromosome resides in a region called the nucleoid. DNA replication begins at the origin of replication and proceeds bidirectionally. As the replicated chromosomes move toward opposite poles, the cell elongates, physically separating the two halves. Once replication is complete, a septum forms at the center, dividing the cytoplasm and yielding two genetically identical daughter cells.
Interphase is the preparatory phase where the cell grows and duplicates its DNA. It consists of three sub‑phases:
Mitosis ensures accurate chromosome segregation. The five stages are:
Cytokinesis overlaps with late mitosis. In animal cells, a cleavage furrow pinches the membrane inward, while plant cells build a new cell plate that becomes a cell wall. Both processes ultimately partition the cytoplasm and organelles into two daughter cells.
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