3

Skin cancer - the abnormal growth of skin cells - most often develops on skin exposed to the sun.

Cell that reproduce by asexual reproduction reproduce constantly.

Three reasons why cells reproduce by asexual reproduction:

• Growth• Repair• Replacement

Cells Multiply By Dividing

! Eukaryotes:

! Mitosis

! Meiosis

! Prokaryotes:

! Prokaryotic (binary) fission

4

Mitosis is Nuclear Division

Chromosomes

! Chromosomes - contain the genetic information (DNA) that is passed from parent to offspring.

5

Chromosomes! Chromosomes have two parts: chromatids held

together by a centromere.

! The chromatids are exact copies of each other and are split apart during mitosis to form single chromosomes.

Centromere

Chromatids

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Chromosome Replication

Replication

One chromatid

sister chromatids

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The 3 Phases of Interphase1. G1 (Gap): Cell is living, doing

normal processes

2. S (Synthesis): DNA replicates

3. G2 (Growth): Cell is expanding, replicating organelles, getting ready for division

! No turning back after S phase starts! Cell will divide!

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What happens after interphase?

MITOSIS

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Cell Division

! Mitosis is NUCLEAR division

! Cytokinesis is CYTOPLASMIC division

! We will call both (together) “Mitosis”

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Check Point:Why Do Cells Divide?

1. Growth

2. Repair

3. Reproduction

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Mitosis

Meiosis

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Before we go any further,Let’s Learn Some Helpful Hand Signs!

PROPHASE

13

METAPHASE

ANAPHASE

14

TELOPHASE

Got It?Now we’ll talk about what happens in …

Prophase Metaphase

Anaphase Telophase

P M

A T

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Make A Table

PROPHASE METAPHASE ANAPHASETELOPHASE & CYTOKINESIS

WHAT IT LOOKS LIKE

WHAT’S GOING ON

PROPHASE

! Chromatin thickens into chromosomes

! Nuclear envelope disintegrates

! Centrioles migrate to opposite poles

! Centrioles begin producing spindle fibers

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Centrioles

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METAPHASE

! Chromosomes line upalong metaphase plate

Spindle fibers are made of

microtubulesSpindle fibers attach at the

centromere of duplicated

chromosomes

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ANAPHASE

! Sister chromatids pulled apart to opposite poles

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TELOPHASE & CYTOKINESIS

! Nucleus reforms

! Chromosomes begin to relax into chromatin (back to G1)

! Cytoplasm splits to separate daughter cells

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CYTOKINESIS (p248)

! Cleavage Furrow

! (no cell wall)

In Animal Cells In Plant Cells

• Cell Plate

• (to form cell wall)

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Could you find the phases on a

prepped slide?

Summary