Mitotic Phase
Mitosis (M Phase) is the part of the cell cycle in which a cell divides into two identical daughter cells, which are genetically identical to each other as well as the "mother" cell.
- Recall that the M Phase of the cell cycle can be subdivided into mitosis and cytokinesis.
- The first portion is also called karyokinesis, which literally just means division of the nuclear contents.
- The second portion, cytokinesis, means separation of the cytoplasmic components into two daughter cells.
- Most of the cell division in our bodies occurs through mitosis.
- Mitosis is for growth, and to replace old and dying cells.
Phases of Mitosis
- Prophase
- Chromosomes start to condense.
- Centrosome begins to form the mitotic spindle structure composed of microtubules which organize chromosomes and move them to the appropriate locations during mitosis.
- The spindle gets longer as the centrosomes move to opposite poles of the cell.
- The nucleolus disappears and nuclear envelope breaks down.
- Prometaphase
- Chromosomes continue to further condense.
- The mitotic spindle grows and begin to attach to the kinetochore of the chromosomes' centromere.
- The kinetochore is a protein located at the centromere of the sister chromatids.
- Metaphase
- Chromosomes align at the metaphase plate (also sometimes called the equatorial plane).
- The two kinetochores of each chromosome (one for each sister chromatid) are attached to microtubules – each attached to an opposite centrosome.
- Maximal condensation of chromosomes, but chromatids are still attached to one another.
- Anaphase
- Sister chromatids separate and are pulled towards opposite ends of the cell towards the two centrosomes.
- Now they are each one chromosome!
- The microtubules that are not attached to chromosomes push apart, causing the cell to elongate and the poles to move away from each other.
- Telophase
- The mitotic spindle is broken down into tubulin monomers that will form the cytoskeleton of daughter cells.
- Chromosomes start to decondense.
- Nuclear envelope begins to form.
Cytokinesis
This is sometimes seen as the second stage of M phase. Is very different for animals and plants.
- Physical separation of cytoplasmic components occurs in this phase.
- Usually starts to occur in late anaphase or telophase.
In animal cells
- The cell "pinches in" at the metaphase plate due to a band of filaments that act like a drawstring. These filaments are composed of a protein called actin.
- The pinching forms a crease called the cleavage furrow.
- Two daughter cells are formed when cytokinesis is complete.
In plant cells
- Remember that plants have cell walls, composed of cellulose, so a new one must form between the daughter cells.
- Vesicles formed from the Golgi apparatus that contain the components necessary for this process (e.g. glucose) go to the metaphase plate.
- A cell plate forms down the middle, splitting the cell into two and forming a cell wall between them.
Photo by MathildaBrinton / CC BY
Ploidy & C-value coefficients
- Ploidy = n = # of chromosomes in a single set
- Example: Humans
- Have 23 distinct chromosomes
- Have 2 sets of chromosomes
- 2n = 2(23) = 46 total chromosomes
- C-value = C = the physical amount of DNA across a single set of chromosomes in pg
- Example: Human cell at Interphase
- Has 23 distinct chromosomes that holds "C" pg of DNA
- Have 2 sets of chromosomes
- 2C = total amount of DNA within the cell
Example: Fill in the table for a diploid cell
