Mitosis & Cytokinesis

Chapter 10

Mitosis

Mitosis

Cell Division

In eukaryotes, cell division occurs in two major stages.

The first stage, division of the cell nucleus, is called mitosis.

The second stage, division of the cell cytoplasm, is called cytokinesis.

Why do cells divide by Mitosis?

Growth of the organism

Repair of tissue damage

Replacement of old cells

Reproduction of some single celled organisms (Which ones?)

AmobeaReproducing

Which single celled organisms reproduce by mitosis?

The protists or member of the kingdom Protista

They are eukaryotic cells & have a nucleus. Mitosis = division of nucleus.

Bacteria DO NOT divide by mitosis because they don’t have a nucleus.

Bacteria reproduce via binary fission

Cells produced by Mitosis…….

Are called daughter cells.

Are identical to the original cell

Are identical to each other

Have the same # of chromosomes

Have an identical chromosome makeup

Skin

A Duplicated Chromosome

one chromatid

its sisterchromatid

One chromosome in the duplicated state

centromere

Diploid vs. Haploid Cells

Diploid= A cell that has 2 sets of chromosomes One set came from each parent (mom

and dad) Chromosomes come in pairs Humans have 23 pairs of

chromosomes for a total of 46 chromosomes per cell

Somatic Cells are body cells (all except sperm and egg) and are diploid

Diploid vs. Haploid Cells

Haploid = A cell with 1 set of chromosomesGametes or sperm or egg are

haploid.In humans, gametes contain 23

chromosomes

Stages of Mitotic Cell Division

Prophase = “1st”Metaphase = “middle”Anaphase = “apart”Telophase = “far or separate”

Interphase “Intermission” Normal metabolic

(cell) activities Major state of the

cell cycle. Cell spends 90% of

time here DNA is in the form

of chromatin, not coiled into chromosomes

The nucleus appears solid. A nucleolus can sometimes be seen.

Late Interphase

The cell prepares for mitosis

DNA doubles (replicates) and forms sister chromatids

Centrioles double in animal cells

Prophase Nuclear membrane disappears

Replicated DNA is condensed

Chromosomes form and can be seen

Spindle fibers start to form

Metaphase

Chromosomes line up at that equator or middle of the cell

The ends of the chromosomes point toward the ends or the poles of the cell.

Spindle & spindle fibers: Pull apart the sister chromatids

Spindle fibers

Anaphase

Chromosomes move to opposite poles

Centrioles are at the poles in animals

Spindle apparatus is at the pole in a plant

Telophase

Chromosomes gather at opposite ends of the cell and lose their distinct shape.

Cell plate or new cells membranes form

Nucleus reappears

Cytokinesis:cytoplasm divides & splits apart

Return to Interphase

New daughter cells each resume the cell cycle in G1 of interphase.

They will each have a period of growth and normal cell activity

before they each divide.

Cytokinesis

Mitosis is over, and the spindle is now

disassembling.

Band of microfilaments at the former spindle equator contracts.

The contractions continue and cut the cell in two.

Cytokinesis in Plants

In plants, a structure known as the cell plate forms midway between the divided nuclei. Cell wall

Cell plate

Stages of Mitosis

Plant versus Animal Mitosis

Plant:Cell wall from

cell plate in telophase

Spindle apparatus

Animal:No cell wallCell

membrane cytokinesis

Centrioles

Cancerous cells……...

1.Divide too many times

2.Divide into more than two cells!

Masses of cells = “tumors” benign malignant