Metaphase — Definition & Diagrams

What's Metaphase?

After prophase, the second phase of mitosis is metaphase.

During this step, the mitotic spindle is completely developed and the centrosomes (consisting of centrioles) are on opposite sides of the cell. The chromosomes align on the "equator" of the cell, also known as the metaphase plate.

Remember how chromosomes are made of sister chromatids? Well, each of these sister chromatids is attached to a spindle fiber from opposite sides of the cell. The picture below illustrates this set-up very well.

Before the cell enters the next step of mitosis, it has to pass a checkpoint.

The cell has to check that all the chromosomes are attached to spindle fibers. This helps to make sure that the chromatids are separated correctly later on, and that the resulting daughter cells end up with the correct genetic material. Checkpoints in cell division often prevent mistakes, like nondisjunction, from occurring.

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

$\color{#8925ae}{\text{Interphase}}$ : 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

Metaphase

After prophase, the cell begins metaphase.

The main event during this phase is chromosomes lining up along the center of the cell. This prepares the cell for the next phase.

It's important to remember that each chromosome consists of two sister chromatids. The chromatids are connected in the middle by a centromere. The mitotic spindle attaches fibers (called kinetochore microtubules) to the centromere and helps align the chromosomes at the middle of the cell onto the metaphase plate.

Before the cell can move on to the next phase of mitosis, it must pass an important checkpoint.

The M checkpoint ensures that the chromosomes are properly attached to spindle fibers. This is important because the chromosomes will be split up in the next phase. Checkpoints like this one prevent major mistakes, like nondisjunction.

(Video) Mitosis: Splitting Up Is Complicated

by CrashCourse

After prophase, during the second phase of mitosis, sister chromatids line up at the center of the cell in something called the metaphase plate. In this video by Crash Course, Hank explains this process.