Cell Division

Honors Biology

Unit 3

What is the cell cycle?

• During the cell cycle, a “parent” cell grows and divides to form 2 “daughter” cells.

• The cycle has three main stages– Interphase– Mitosis– Cytokinesis

Why does a cell need to divide?

1. DNA Overload

• DNA overload is when the DNA has too many tasks to do (such as making proteins) and not enough DNA to get the job done efficiently. To prevent DNA overload cells stay small to limit a cells work load.

2. Material Transfer

• Materials move into and out of cells Cells need to take in materials such as oxygen, water and glucose. Cells need to get rid of materials such as carbon dioxide, salts, other waste.

• Large cells lose efficiency in this process – surface area and volume do NOT increase at the same rate.

Why does a cell need to divide?

Growing to an adult

A. The size of the organism’s cells _________________________

B. The number of cells the organism has? ___________________________

Stays the same size

Increases as it gets bigger

The Cell Cycle

• Animation

M

G1

SG2

Stage 1 Interphase

• During Interphase cells:– Grow to mature size

• Mitochondria and chloroplasts are duplicated

– Replicate (copy) DNA • Each cell needs instructions

– Prepare for cell division• Centrioles become visible

• Most of a cells life is spent in Interphase.

Chromosomes

• Are made of DNA• Each chromosome consists of sister

chromatids attached at a centromere

Stage 2: Mitosis

• The cells nucleus divides into two nuclei• There are four phases

– Prophase– Metaphase– Anaphase– Telophase

P M A T

Animal Cell Mitosis- Video

Prophase

• 1st stage of Mitosis• Chromatin condenses into chromosomes• Centrioles separate and a spindle fiber

begins to form.• Nuclear membrane breaks down

Prophase

Metaphase

• 2nd Phase of Mitosis• Chromosomes line up in the middle of the

cell.• Each chromosome is connected to a

spindle fiber.

Metaphase

Anaphase

• 3rd Phase of Mitosis• The sister chromatids separate at the

centromere and move to opposite ends of the cell.

Anaphase

Telophase

• 4th Stage of Mitosis• Chromosomes gather at opposite ends of

the cells and lose their shapes (return to chromatin form)

• Two new nuclear membranes form, one for each cell.

Telophase

Stage 3: Cytokinesis

• The cytoplasm pinches in half.• Each daughter cell has an identical set of

duplicate chromosomes

Cytokinesis

Cytokinesis in the Animal Cell Animated

Cytokinesis