profáz

Profáz is a term used in biology to describe the initial stage of cell division, specifically mitosis and meiosis. During prophase, the cell prepares for division by undergoing several key transformations. The most visually striking event is the condensation of chromosomes. Before prophase, the genetic material exists as loosely packed chromatin. As prophase begins, this chromatin coils and folds, becoming shorter and thicker, making the individual chromosomes visible under a light microscope. Each chromosome, in this early stage, consists of two identical sister chromatids joined at a central region called the centromere.

Another significant event of prophase is the breakdown of the nuclear envelope, the membrane surrounding the nucleus. This breakdown allows the chromosomes to access the cytoplasm and interact with the spindle fibers. Simultaneously, the nucleolus, a structure within the nucleus involved in ribosome synthesis, disappears. In animal cells and some lower plants, a structure called the centrosome duplicates and moves to opposite poles of the cell. These centrosomes organize the formation of the mitotic spindle, a structure composed of microtubules that will eventually pull the chromosomes apart. The process of prophase sets the stage for the subsequent phases of cell division by organizing and preparing the genetic material and the cellular machinery for separation.