Mitosis Overview

Objectives• Name and describe the two types of

reproduction.• Explain what happens during the cell

cycle.• Explain what happens in the stages

of mitosis.• Discuss how mitotic cell division in

unicellular and multicellular organisms are controlled.

Terms to know:

-mitosis -cytokinesis-interphase -prophase-metaphase -anaphase-telophase -cell cycle-asexual reproduction -

chromosomes -sexual reproduction -binary fission-budding -spores-gametes -chromatin

Why must cells divide:

Cells must divide in order for an organism to be able to:

• Grow• Maintain and repair body tissues• Reproduce

Function of mitotic cell division

• Mitosis is important for the growth, maintenance, repair, reproduction of eukaryotic body cells.

• Kidney, liver, skin, heart, pancreas cells etc. all reproduce by mitotic cell divisions.

• Mitosis results in 2 daughter cells that have the exact same DNA as the mother cells.

Two major types of reproduction

1. Asexual reproduction: Only 1 parent organism reproduces by itself, no sex cells are involved. Offspring are genetically identical to parent.

2. Sexual reproduction: Two parent organisms reproduce to form a new organism. Gametes or sex cells (sperm and egg) are involved. Offspring are contains genes from both parents.

Two types of reproduction:

•Asexual reproduction occurs in single celled organisms, some plants, and some animals.

•Sexual reproduction occurs in most animals and plants.

Cell Division

• Before it becomes too large, a growing cell must divide forming two daughter cells.

• The process by which a cell divides into two new daughter cells is called cell division.

Cell Division• Before cell division occurs, the cell

replicates, or copies, all of its DNA.• This replication of DNA solves the

problem of information storage because each new daughter cell gets one complete set of genetic information.

• Thus, each daughter cell now contains its own genetic “library”.

The cell cycle and mitosis

• During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells each of which then begins the cycle again.

•Mitosis: A process of the cell cycle that occurs when a cell with a distinct nucleus divides to form two daughter cells.

5 Phases of the cell cycle1. The cell grows and develops (G1)2. The genetic material is replicated

inside the parent cell (S)3. The cell continues to grow and

develop (G2) 4. The nucleus divides in two

separating the genetic material into two equal parts (mitosis)

5. The cytoplasm divides forming two new daughter cells (cytokinesis)

Cell cycle and mitosis

Questions:

1. What does the nucleus contain and why must it divide?

2. What kinds of cells can undergo mitosis?

(eukaryotic or prokaryotic)

Mitosis and changes in the nucleus

• DNA is the genetic information needed to make important cell structures. It also determines how the organism will look, behave, and function.

• Before a cell divides, the DNA must be replicated so that each new daughter cell has a copy of the information.

Mitosis and changes in the nucleus

• Before the cell divides, the DNA in the nucleus appears as loose fibers called chromatin.

• Before mitosis begins, the DNA must be replicated.

• As the cell enters mitosis, the chromatin coils up into structure called chromosomes.

Mitosis and changes in the nucleus

• Imagine: Each strand of DNA within each of your cells is about 6 feet long. The DNA becomes so tightly coiled into the chromosomes that it can actually fit into a microscopic cell!!

• Humans have 46 chromosomes in each of our body cells.

What exactly is a chromosome?Chromosomes are

composed of tightly coiled DNA and proteins called histones, which allow the DNA to coil into these compact structures.

Chromosomes contain genes which code for various traits.

Chromatid

Mitosis and changes in the nucleus

• During cell division, before mitosis, it is the chromosomes that duplicate.

• Why must the chromosomes duplicate before mitosis?

Interphase and Mitosis

• When a cell is not dividing, it is in interphase.

• During interphase the cell:–Grows in size–Replicates its chromosomes (they double in number)

–Metabolic activity is at its highest

Mitosis –Division of the nucleus

• Mitosis involve 4 phases.1. Prophase: 2. Metaphase: 3. Anaphase:4. Telophase:

Plainedge Made A Touchdown

Prophase• The chromatin

thickens and coils into chromosomes

• The nuclear membrane disappears

• Mitotic spindle fibers form from centrioles

Metaphase• Spindle fibers

align the chromosomes along the middle of the cell nucleus. This line is called the metaphase plate.

• This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.

Anaphase• The paired

chromosomes separate at the kinetochores and move to opposite sides of the cell.

• Kinetochore: part of chromosomes where spindle fiber attaches

• Motion results from a combination of kinetochore movement along the spindle microtubules

Kinetochore and Spindle Microtubules

Telophase• Chromatids arrive at

opposite poles of cell, and new membranes form around the daughter nuclei.

• The chromosomes disperse and are no longer visible under the light microscope.

• The spindle fibers disperse, and cytokinesis or the partitioning of the cell may also begin during this stage.

Cytokinesis• In animal cells,

cytokinesis results when a fiber ring composed of a protein called actin around the center of the cell contracts pinching the cell into two daughter cells, each with one nucleus.

• In plant cells, the rigid wall requires that a cell plate be synthesized between the two daughter cells.

Whitefish Mitosis

interphase metaphaseprophase

anaphase telophase

What Phase is this?

• Prophase• Nuclear membrane is

gone.• DNA condensed into

chromosomes

How about this?

• Anaphase• Chromosomes are

being pulled apart to opposite ends of the cell.

What Phase is this?

• Telophase• Nuclear membrane

has reappeared• DNA is now in

chromatin form.• Cell membrane

pinches cell into 2 new daughter cells.

What Phase is this?

• Metaphase• Chromosomes are

lined up in the center of the cell.

• Spindle fiber network is visible

What Phase is this?

• Interphase• Nuclear membrane is

visible• DNA in form of

chromatin.

Related Websites

• http://www.cellsalive.com/mitosis.htm• http://www.biology.arizona.edu/cell_bio/tutorials/cell_cy

cle/cells3.html• http://www.sci.sdsu.edu/multimedia/mitosis/• http://biologyinmotion.com/cell_division/• http://www.life.umd.edu/CBMG/faculty/wolniak/wolniak

mitosis.html• http://www.bio.unc.edu/faculty/salmon/lab/mitosis/mitosi

s.html