1

Cell Cycle, Mitosis

How do little elephants grow up to be BIG elephants?

2

Why do animals shed their skin?

The process of asexual

reproduction begins after a sperm fertilizes an egg.

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

����

����

Chromosome Replication

Replication

One chromatid

sister chromatids

����

6

When cells

divide, sister

chromatids

separate so that

each cell has the

correct number of

chromosomes.

����

46 … or … 23?

� 23 homologous pairs of (human) chromosomes (46 total, full number)

� Somatic (body) cells (every cell except sperm and egg)

• 23 individual chromosomes (halfthe full number)

• Gametes (Sex Cells: sperm and egg)

Diploid Haploid

����

7

Human Chromosomes

� Human diploid cells have

46 CHROMOSOMES – 2 COPIES OF 23 DIFFERENT CHROMOSOMES.

����

The Cell Cyclefor Somatic Cells (p244-245)

� 2 Main Parts1) Interphase (life,

growth)

2) Mitosis (division of nucleus)

� Consider cytokinesis(division of cytoplasm) as part of mitosis

1

2

����

8

Interphase

� Longer part of the

cell cycle (90%)

� 3 Phases

I. G1 (Gap)

II. S (Synthesis)

III. G2 (Growth)

During Interphase, DNA is

relaxed and spread out thinly

Thin, stringy, “Invisible,” chromosomes are

called CHROMATIN

����

9

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!

����

What happens after interphase?

MITOSIS

10

Cell Division

� Mitosis is NUCLEAR division

� Cytokinesis is CYTOPLASMIC division

� We will call both (together) “Mitosis”

����

Check Point:

Why Do Cells Divide?

1. Growth

2. Repair

3. Reproduction

����

Mitosis

Meiosis

11

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)

1) PROPHASE

2) METAPHASE

3) ANAPHASE

4) TELOPHASE

• (With Cytokinesis)

����

12

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

15

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

����

Centrioles

16

METAPHASE

� Chromosomes line upalong metaphase plate

Spindle fibers

are made of

microtubulesSpindle fibers

attach at the

centromere of

duplicated

chromosomes

����

ANAPHASE

� Sister chromatids pulled apart to opposite

poles

����

17

TELOPHASE & CYTOKINESIS

� Nucleus reforms

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

� Cytoplasm splits to separate daughter cells

����

CYTOKINESIS (p248)

� Cleavage Furrow

� (no cell wall)

In Animal Cells In Plant Cells

• Cell Plate

• (to form cell wall)

����

18

What could happen if cytokinesis fails?

Can You Identify

The Phases Of

Mitosis?

19

Could you find the phases on a

prepped slide?

Summary