CELL DIVISION

Key Concepts

• What events take place during the three stages of the cell cycle?

Key Terms

• cell cycle –

• interphase –

• replication –

• The regular sequence of growth and division that cells undergo.

• The stage of the cell cycle that takes place before cell division occurs.

• The process by which a cell makes a copy of the DNA in its nucleus.

Key Terms

• mitosis –

• chromosome –

• cytokinesis –

• The stage of the cell cycle during which the cell’s nucleus divides into two new nuclei and one copy of the DNA is distributed into each daughter cell.

• A double rod of condensed chromatin; contains DNA that carries genetic information.

• The final stage of the cell cycle, in which the cell’s cytoplasm divides, distributing the organelles into each of the new cells.

Introduction

• A multicellular organism grows in size because it’s cells are increasing in number.

Three Stages of Cell Division

• Stage 1: Interphase

• Stage 2: Mitosis

• Stage 3: Cytokinesis

• The period before cell division.

• One nucleus divides to create two.

• Completes the process of cell division.

Stage 1: Interphase

The period before cell division.

The Resting Stage?

• Growing– The cell grows to full

size.– The cell makes new

structures it needs or duplicates others.

• Copying DNA– A replication (exact

copy) for the new cell is made.

• Preparing for Division– Centrioles (structures

used for cell division) are made.

Stage 2: Mitosis

One nucleus divides to create two.

It’s All About the . . .

CHROMOSOMES!

The Many “Faces” of A Chromosome

• Chromatin (threadlike)– A mass of genetic material

composed of DNA and proteins that condense to form chromosomes.

• Chromosome (letter X)– A condensed, double-rod,

form of chromatin.• Chromatid

– Two identical strands of DNA that form a chromosome.

• Centromere– A structure that holds the

chromatids together.

CHROMATIN

CHROMOSOME

Phase 1: Prophase

• Chromosomes and spindle fibers form.

• Nuclear envelope (membrane) breaks down.

Phase 2: Metaphase

• Chromosomes line up across the center and attach to a spindle fiber.

Phase 3: Anaphase

• Centromeres split.

• Chromatids separate and move to opposite ends.

Phase 4: Telophase

• Chromosomes stretch out.

• New nuclear envelope (membrane) forms around chromosomes.

Stage 3: Cytokinesis

Completes the process of cell division.

Like Mother Like Daughter

• Cell pinches in two.

• Each daughter cell has the same number of identical chromosomes.

Animal Cells vs. Plant Cells• The cell membrane

squeezes together around the middle of the cell.

• The cytoplasm pinches into two cells.

• A cell plate forms between the two new nuclei.

• The cell plate gradually develops into new cell membranes.

• New cell walls then form around the cell membranes.

Animations• Control of the Cell Cycle

– http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__control_of_the_cell_cycle.html

• How the Cell Cycle Works– http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/

animation__how_the_cell_cycle_works.html

• Mitosis & Cytokinesis– http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/

animation__mitosis_and_cytokinesis.html

• Animal Cell Mitosis– http://iknow.net/player_window.html?url=media/

prophase_video_auto.swf&width=360&height=285

• Plant Cell Mitosis– http://iknow.net/player_window.html?url=media/plant_mitosis_auto.swf&width=360&height=2

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What is the Purpose of Cell Division?

• When the cell volume/surface increases, then a cell must divide or split into two, because if it doesn't then it would literally just be one huge blob.

• Cell division is necessary for all life, without it then you would barely exist.

• Cells need to divide because if you lose older cells, how else would you replace them?

• Your body consists of millions or billions of cells, and without them you wouldn't be you!