Cell DivisionThe Cell Cycle and Mitosis

Why do cells divide?

•Growth

•Repair

•Reproduction

Chromosomes

• Carry genetic information from one generation of cells to the next

• Not visible in cells except in cell division

Cell Division

• Process by which a cell divides into two daughter cells

• Before division, the cell replicates all its DNA

• Each daughter cell will get one complete set of genetic information

Cell Division- Prokaryotes• Binary fission:

asexual cell division of prokaryotes that produces identical offspring

• Three Steps:1. DNA is copied2. Cells begin to divide3. Two identical cells

Binary Fission

Bacterial cell dividing by binary fission

E. Coli dividing by binary fission

Cell Division- Eukaryotes

• Nucleus first and then the Cytoplasm divides

• There are two kinds:1. Mitosis2. Meiosis

• Cell cycle: set of events making up the life of a cell; composed of interphase and cell division

The Cell Cycle

Interphase• The time between cell

divisions where the cell spends most of its life

• Cell is in a resting phase, performing cell functions

• Composed of G1, S and G2 phases

Interphase

Interphase: G1, S, G2

•G1 (Gap 1)- Cells grow to mature size

•S (Synthesis)- DNA is copied

•G2 (Gap 2)- cell organelles grow and prepare for division

Mitosis• Division of nucleus

• Daughter Cells wind up with the same # of chromosomes

• There are 4 phases:1. prophase 3. anaphase2. metaphase 4. telophase

Prophase• Chromosomes become visible

• Centrioles separate and move to opposite sides of nucleus

• Spindle fibers form

Prophase• Nucleolus disappears

• Nuclear Envelope breaks down and disappear

• Prophase is the longest phase of cell division

Prophase

Metaphase• Chromosomes line up along the

equatorial plate (middle of the cell)

• Chromosomes connect to spindle fibers at centromere

• Metaphase is the shortest phase

Metaphase

Anaphase

• Sister chromatids separate and move to opposite poles

• When chromatids separate, they are considered individual chromosomes.

Anaphase

Telophase• Nuclear envelope forms around each

group of chromosomes

• Chromosomes relax back into chromatin

• Spindle fibers disassemble.

• Cytokinesis begins

Telophase

Cytokinesis• The process by which the

cytoplasm divides and one cell becomes two individual cells

• Different in plants and animals– Animals- cell pinches inward to

form a cleavage furrow– Plants- a cell plate forms between

the two new cells forming a cell wall

Cytokinesis- Animal Cell

Cytokinesis- Plant Cell

Cytokinesis- Plant vs. Animal