Mitosis

Interphase

To grow and heal and repair, you need more cells. Mitosis happens more frequently in embryos. We constantly need to create more cells. It also happens in asexual reproduction.

Proliferation: Rapid increase in cell number through mitosis.

Start with G1, which is growing and doing its job. The G stands for gap, but it basically means growth. Then you go through the synthesis, or s, phase, where you synthesize DNA (replicate it). After that, you go through another G phase, but you also start preparing for mitosis. This is all called interphase.

Interphase: The gap between mitosis where a cell grows, does its job, prepares for mitosis, and synthesizes proteins.

Chromosomes: Condensed form of DNA. If before S phase, looks like a chromatid

Chromatid: half of a chromosome. Only occurs after S phase.

Chromatin: Spaghetti for of DNA

Centromere: center of a chromosome

To count chromosomes, count centromeres

Diploid: 2 sets of each chromosome, somatic cells - mitosis

Haploid: 1 set of each chromosome, gametes - meiosis

Gamete: sex cell

What happens in interphase:

• Metabolic reactions: respiration to produce ATP

• Protein synthesis

• Organelle numbers are increased

• DNA is replicated

S phase goes from one chromosome to one chromosome (it now has two chromatids). The chromatids separate during mitosis.

We super coil (turn DNA from spaghetti to little bitty thing) so we can split it exactly and fit it inside the nucleus.

Mitosis

Mitosis: the division of the nucleus into two genetically identical nuclei

Cytokinesis: the splitting of the cell, not part of mitosis.

Prophase:

• DNA condenses into chromosomes

• the nuclear membrane breaks down

• the centrioles start creating spindle fibers

• the centrioles move to the poles

Metaphase

• Chromosomes go to the middle of the cell

• Spindles attach to the chromosomes at the centromere

• Quick phase, visible by chromosomes in middle

• The nucleus is completely gone

• The equator is the middle of the cell (metaphase plate)

• Kinetochore: when the spindles connect to the centromere, a kinetochore is formed

Anaphase

• In a microscope, you see two distinct lines

• The centrioles act like gears and pull the chromatids away from each other

Telophase

• The nuclear membranes reappears

• The spindle fibers detach and break down

• DNA relaxes

• You can’t see individual chromosomes in telophase

• Late telophase is where the plasma membrane pinches

Cytokinesis is the splitting of the cell.

In animal cells: A microfilament ring forms around the equator, and it tightens into a cleavage furrow, and then you have two cells.

In plant cells: you form a cell plate and build the cell wall between both cells

Result of mitosis: Two identical diploid daughter cells with the same number of chromosomes in each and they have the same DNA

Mitotic Index = number of cells in mitosis / total number

Too much is cancer

Phases of Mitosis practice