Prophase — Definition & Diagrams

What's Prophase?

Prophase is the first phase of mitosis. This part of mitosis is all about preparing.

During this phase, the DNA forms into chromosomes, which we can actually see. Chromosomes are condensed chromatin. In this phase, the chromosomes consist of two identical chromatids called sister chromatids.

The microtubule-forming organelles called centrioles separate and move to opposite poles of the cell. Wire-like structures called spindles are attached to both of the centrioles. The spindles stretch from one centriole to the other, spanning the entire cell.

Next, the nuclear envelope goes away and the nucleolus disappears. Finally, small fibers of the spindle attach themselves to the center of the chromosomes using something called a kinetochore. After this step is complete, the cell moves on to the next step of mitosis.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Interphase}}$ : The longest part of the cell cycle where the cell grows and DNA is replicated to prepare for nuclear division

$\color{#8925AE}{\text{Nuclear Division}}$ : The process of dividing the nucleus

$\color{#8925AE}{\text{Mitosis}}$ : The process of dividing one nucleus into two identical nuclei. Occurs in all cells except for sex cells

$\color{#8925AE}{\text{Cytokinesis}}$ : The final step of cell division where the cytoplasm is divided to form daughter cells

$\color{#8925AE}{\text{Diploid Cell}}$ : Cell that contains two sets of chromosomes

Prophase of Mitosis

This is the first stage of cell division. During this phase, the nuclear envelope, which surrounds the DNA, is destroyed by a bunch of proteins and it disappears. The DNA is in a loose, unraveled chromatin form, but it is condensed into chromosomes.

The chromosomes look like an X. Each half of the X is an individual, identical chromosome called a chromatid. These pairs of two chromosomes are called sister chromatids. They are linked at the center of the X called the centromere.

The mitotic spindle also begins to form. Organelles called centrosomes consist of structures called centrioles, which produce spindle fibers. The centrosomes begin to move towards opposite ends of the cell, and spindle fibers begin to elongate during this phase. These fibers will later be used to separate the sister chromatids of each chromosome into separate daughter cells.

(Video) Mitosis: Splitting Up Is Complicated

by CrashCourse

Prophase is the first step of mitosis. In this stage, the nuclear envelope breaks, letting the genetic material float free. Centrosomes start to form structures which help the cell through the rest of mitosis.