Mitosis & Cytokinesis

Why do Eukaryotic cells divide by Mitosis?

Growth & Repair for multicelled organisms

Reproduction of single celled organisms

AmobeaReproducing

Cells dividing by Mitosis…….

• Identical to original cell

• Same chromosome #

• Identical chromosome makeup

Skin

What are chromosomes?A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many

genes, regulatory elements and other nucleotide sequences.

What are chromosomes?A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many

genes, regulatory elements and other nucleotide sequences.

What are chromosomes?A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many

genes, regulatory elements and other nucleotide sequences.

Sister Chromatids

So where is DNA located?

In the Nucleus

In the Chromosomes

Cell division requires coordinated division of chromosomes (mitosis) …..

…… and division of the cytoplasm (cytokinesis).

From Birth to Rebirth, a Cell Progresses Through Characteristic Stages That Constitute the Cell Cycle.

In multicellular organisms like us, progress through the cell cycle is carefully regulated.

Stages of Mitotic Cell Division

• Interphase - intermission• Prophase - 1st• Metaphase - middle• Anaphase - apart• Telophase – far or seperate

Interphase

• “Intermission”

• Normal metabolic activities

• Major state • DNA = chromatin

Late Interphase

• Prepares for mitosis• DNA doubles = Sister chromatids• Centrioles double in animals

Prophase• Nuclear membrane

disappears• Doubled DNA =

condensed• “chromosomes”

visible• Spindle fibers

Metaphase

• Chromosomes line up mid- cell

• Facing inward

Anaphase• Chromosomes move to

opposite poles at Centrioles in animals

• Spindle apparatus in plants

Telophase• Cells divide• Cell plate or

membranes form• Nucleus reappears

Cytokinesis: cell’s cytoplasm divides & splits apart

Plant versus Animal Mitosis

Plant:• Cell wall from cell plate in telophase• Spindles

Animal:• No cell wall membrane during cytokinesis• Centrioles

In Animal Cells, a Cleavage Furrow Forms and Separates Daughter Cells

Cleave furrow in a dividing frog cell.

Animal Telophase

Interphase

The Plant Cell Wall Forces Cytokinesis to Play by Different Rules

Plant AnaphaseInterphase

Spindle & spindle fibers: Pull apart the sister chromatids

Spindle fibers

Returns to Interphase

• “Intermission”• Normal metabolic activities• Major state • DNA = chromatin

DNA and Its Faithful Replication – The Knit of Identity

Because DNA stores genetic information and is faithfully replicated, information is passed largely unaltered from cell-to-cell, generation-to- generation.

Proteins and Their Production – The Primary Reason for DNA

Cell Division DemandsCoordination of DNA Replication, Mitosis and Cytokinesis

DNA Replication – Simple in Principle, Complicated in Practice

DNA is Packaged into Chromosomes

DNA in the cell is virtually always associated with proteins.

The packaging is impressive – 2 meters of human DNA fit into a sphere about 0.000005 meters in diameter.

chromatin

duplicatedchromosome

The Link Between DNA Replication and Chromosome Duplication

DNA is Condensed into Visible Chromosomes Only For Brief Periods in the Life of a Cell

95% of the time, chromosomes are like this.

(chromatin)

Easily visible chromosomes are apparent perhaps 5% of the time in an actively growing cell and less in a non-growing cell.

A Karyotype is an Arranged Picture of Chromosomes At Their Most Condensed State

A normal human karyotype

Boy or girl?

Note that almost all chromosomes come in homologous pairs.

From Birth to Rebirth, a Cell Progresses Through Characteristic Stages That Constitute the Cell Cycle

In multicellular organisms like us, progress through the cell cycle is carefully regulated.

The Knit of Identity - Mitosis Precisely and Evenly Divides Duplicated Chromosomes

Precisely dividing the duplicated chromosomes has the consequence of providing each new cell with an identical and complete set of genetic instructions.

interphase prophase metaphase

Mitosis Precisely and Evenly Divides Duplicated Chromosomes

Cytokinesis is the process of cell division and it is distinct and separable from mitosis.

Mitosis in Action

Blue shows DNA, green shows spindle fibers.

Cancerous cells……...

1.Divide too many times

2.Divide into more than two cells!

• Masses of cells =

• “tumors”

• benign

• malignant

Cancer Is One Outcome of A Runaway Cell Cycle

Licentious division - prostate cancer cells during division.