Cell Division

Why Cells Make More Cells1. Most cells go through a series of changes in order

to maintain homeostasis.2. Cells need to reproduce (divide) when their surface area

can no longer supply the much larger volume with nutrients and get rid of wastes.

Surface Area (length x width x 6)Volume (length x width x height)

Ratio of Surface Area to Volume

Vocabulary

1. Chromatin: the relaxed, uncoiled state of the chromosome

2. Chromatid: one of two identical “sister” parts of a duplicated chromosome

3. Chromosome: threadlike structures within the nucleus containing genetic information that is passed on from generation to generation

4. Centromere: chromosome region that joins 2 sister chromatids

A: centromere

chromo─ color ─soma: body─id: self, body

centro─ center─mere: part

B: chromatids

Chromosomes1. Chromosomes: made up of

DNA & proteins

2. Carry the cell’s coded genetic information

3. Different organisms have a different number of chromosomes

Fruit flies have 8 chromosomes in each

body cell

Frogs have 26 chromosomes in each body cell

Humans have 46 chromosomes in each body cell

Cell Cycle1. Cell cycle: Sequence of events between the time a cell

divides to form 2 daughter cells & the time those 2 cells divide

2. Consists of Interphase and M-phase (Mitosis & Cytokinesis)

3. G0 ─ cells that exit the cell cycle

Interphase: 3 Phases

1. G1 phase: Growth Phase

a. Cell performs all life’s activities: protein synthesis, waste removal, organelle synthesis, etc.

2. S phase: DNA Replication

a. DNA makes a copy of itself

b. Produces 2 identical sets of chromosomes

3. G2 phase: Preparation

a. Cell produces centrioles & spindle fibers needed to move the chromosomes

Mitosis Discovered

Walther Flemming first discovered mitosis in 1870 and reported is discovery of chromosomes and mitosis in 1882.

Metaphase in a salamander celldrawn by Walther Flemming from a stained slide.

Mitosis Review 1. Two main stages of the M-phase

a. Mitosis: division of the nucleus b. Cytokinesis: division of the

cytoplasm2. Produces 2 cells called daughter cells a. Cells are genetically identical3. Mitosis is source of new cells for a. Growth b. Development c. Repair d. Replacement of old cells4. Cells that go through mitosis: skin,

bone, muscle, liver5. Cells that RARELY go through mitosis:

nerve cells

Normal red blood cells only live for 120 days. Then they die & stem cells make new ones.

Mitosis

1. Described as movement of chromosomes

2. Continuous series of events

3. Divided into four phases so that it is easier to understand

Cell Cycle

Diploid verses Haploid Di─ doubleHaplo─ single-oid: like

23Sperm cell

23

Egg cell

46

Fertilized Egg cell

Fertilization

Haploid: 1n; 1 set of chromosomes•The egg and sperm cell are haploid

Diploid: 2n; 2 sets of chromosomes•The fertilized egg cell is diploid

Develops into

All of the cells that make up the organism are diploid

Each kind of cell:•Skin•Muscle•Bone•Nerve

•Are ALL DIPLOID

1. Normal cells contain check points to regulate the cell cycle, & stop at appropriate check points.

2. Cancerous cells do not respond to check points and continue rapidly through the cell cycle. This results in masses of undefined cells called tumors.

3. Cancer cells do not mature; they become more immature.

Do not enter into G0

Cancer Cells