Cell Cycle, Mitosis

How do little elephants grow up to be BIG elephants?

Why do animals shed their skin?

The process of asexual reproduction begins after a sperm fertilizes an egg.

Three reasons why cells reproduce by asexual reproduction: Growth Repair Replacement 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.

Cells Multiply By Dividing Eukaryotes: Mitosis Meiosis Prokaryotes: Prokaryotic (binary) fission

Mitosis is Nuclear Division What is found in the nucleus?

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

 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. Chromatids  Centromere

Chromosome Replication One chromatid  Replication sister chromatids

 When cells divide, sister chromatids separate so that each cell has the correct number of chromosomes.

 46 … or … 23? Diploid Haploid 23 homologous pairs of (human) chromosomes (46 total, full number) Somatic (body) cells (every cell except sperm and egg) 23 individual chromosomes (half the full number) Gametes (Sex Cells: sperm and egg)

 Human Chromosomes Human diploid cells have 46 CHROMOSOMES – 2 COPIES OF 23 DIFFERENT CHROMOSOMES.

The Cell Cycle for Somatic Cells (p244-245)  The Cell Cycle for Somatic Cells (p244-245) 2 Main Parts Interphase (life, growth) Mitosis (division of nucleus) Consider cytokinesis (division of cytoplasm) as part of mitosis 2 1

Interphase Longer part of the cell cycle (90%) 3 Phases G1 (Gap) S (Synthesis) G2 (Growth)

During Interphase, DNA is relaxed and spread out thinly  During Interphase, DNA is relaxed and spread out thinly Thin, stringy, “Invisible,” chromosomes are called CHROMATIN

The 3 Phases of Interphase  The 3 Phases of Interphase G1 (Gap): Cell is living, doing normal processes S (Synthesis): DNA replicates G2 (Growth): Cell is expanding, replicating organelles, getting ready for division No turning back after S phase starts! Cell will divide!

What happens after interphase? MITOSIS

Cell Division  Mitosis is NUCLEAR division Cytokinesis is CYTOPLASMIC division We will call both (together) “Mitosis”

Check Point: Why Do Cells Divide?  Check Point: Why Do Cells Divide? Growth Repair Reproduction Mitosis Meiosis

In Mitosis: diploid, somatic cells divide to become  In Mitosis: diploid, somatic cells divide to become daughter cells (mitosis makes exact copies of cells) (*circle*) … diploid / haploid (*circle*) … somatic / gamete

Mitosis Has 4 Main Phases Plus Cytokinesis (p246)  Mitosis Has 4 Main Phases Plus Cytokinesis (p246) PROPHASE METAPHASE ANAPHASE TELOPHASE (With Cytokinesis)

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

PROPHASE

METAPHASE

ANAPHASE

TELOPHASE

Got It? Now we’ll talk about what happens in … M Prophase Metaphase A T Anaphase Telophase

TELOPHASE & CYTOKINESIS Make A Table PROPHASE METAPHASE ANAPHASE TELOPHASE & CYTOKINESIS WHAT IT LOOKS LIKE WHAT’S GOING ON

PROPHASE  Chromatin thickens into chromosomes Centrioles Chromatin thickens into chromosomes Nuclear envelope disintegrates Centrioles migrate to opposite poles Centrioles begin producing spindle fibers

METAPHASE  Chromosomes line up along metaphase plate Spindle fibers are made of microtubules Spindle fibers attach at the centromere of duplicated chromosomes Chromosomes line up along metaphase plate

 ANAPHASE Sister chromatids pulled apart to opposite poles

TELOPHASE & CYTOKINESIS  Nucleus reforms Chromosomes begin to relax into chromatin (back to G1) Cytoplasm splits to separate daughter cells

CYTOKINESIS (p248)  In Plant Cells In Animal Cells Cell Plate Cleavage Furrow (no cell wall) Cell Plate (to form cell wall)

What could happen if cytokinesis fails?

Can You Identify The Phases Of Mitosis?

Could you find the phases on a prepped slide?

Summary