The Cell CycleMitosis

Chromosomes

What is the role of chromosomes in cell division? -needs to be duplicated

Genetic information is bundled into packages of DNA known as chromosomes

Chromosomes make it possible to separate DNA precisely during cell division

Prokaryotic Chromosomes

Prokaryotes

•lack membrane bound nuclei

•lacks most organelles contained in Eukaryotic cells

•MOST prokaryotes contain a single, circular DNA chromosome

The Prokaryotic Cell Cycle - Binary Fission

Eukaryotic Chromosomes

Eukaryotic Cells

•have much more DNA than prokaryotes

•therefore, contain multiple chromosomes

DNA + Protein (histones) = Chromatin

The Eukaryotic Cell Cycle

(cell growth)

(Prep. for Mitosis)

(replication)

Mitosis - Phase One = Prophase

•Longest phase of mitosis

•Chromatin condenses = visible chromosomes

•Centrioles migrate towards opposite ends of the cell, forming spindle fibers along the way

•Nuclear envelope breaks down

Phase Two = Metaphase (M=’middle’)

•Generally shortest phase

•Duplicated chromosomes line up across center of cell

•Spindle fibers attach to centromereso (now at opposite ends of cell)

Phase Three = Anaphase (A=’apart’)

• Sister chromatids begin to separate

• Spindle fibers act like a tractor beam

• Each sister chromatid is now considered an individual chromosome

Phase Four = Telophase

•Condensed chromosomes return to a ‘tangle’ of chromatin

•Nuclear envelope re-forms

•Spindle fibers break apart

•Mitosis = Complete

Cytokinesis - final splitting of cells

Animal Cells

•Membrane drawn inward until the cytoplasm pinches into two equal parts

Plant Cells

•Cell wall is too rigid to flex inward

•Cell plate forms halfway between divided nuclei