Cell Growth and

Division

I. Background InfoA. Why Do Cells Divide?

1. Growth of organism2. Repair damaged cells3. Reproduction in microorganisms

B. Why are cells so tiny?1. To maximize the surface area to volume ratio.

What is the surface area and volume of a 4 cm cube?

h

w

d

Surface Area (SA) = (h) x (w) x (# of sides)

4 x 4 x 6 = cm2

Volume (V) = (h) x (w) x (d)

4 x 4 x 4 = cm3

SA/V =

96

64

3/2 or 1.5

What if we cut the cube into eight 2 cm cubes?

Volume 2 x 2 x 2 x 8 = cm3

Surface Area 2 x 2 x 6 x 8 = cm2

SA/VOL = 3

192

64

2. Having twice the surface area and the same volume allows for a more efficient exchange of materials (nutrients, wastes, O2, CO2 and H2O)

a) If a cell becomes too large it can’t transport materials across the membrane fast enough

3. DNA “Overload”a) Cell does not make more copies of DNA as

it grows; therefore the nucleus is limited in how much cell activity it can control

Cell Size Movie

II. ChromosomesA. Chromosomes (DNA) carry all the genetic

information for the organism and are passed on from one generation to the next

B. Every species has a specific # of chromosomes (Human = 46, Chimp = 48, Mosquito = 6, Adder’s tongue fern = 1262)

C. Made up of chromatin1. Made of DNA twisted around histone

proteins.2. Compactly folded and coiled to form a

chromatid. Why?

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

Draw Fig. 10-3 pg. 244

D. Prior to division cells must duplicate their DNA Why?

E. Two identical “sister” chromatids are formeda) Attached by the

centromere

III. The Cell CycleA. Consists of Interphase and M phase (mitosis and

cytokinesis)

III. The Cell CycleB. Interphase

1. Cell’s nucleus and nucleolus are clearly visible.2. Chromosomes have not appeared.

3. Consists of 3 phases:a)G1 phase - cell growth right after cell divisionb)S phase - DNA replication c)G2 phase - replication of cell organelles (to

prepare for division) and synthesis of cell division structures

4. Cell spends ~90% of its time in interphase

The Cell Cycle

Draw Fig. 10-4, pg. 245

M phase

G2 phase

S phase

G1 phase

Interphase Movie

C. Mitosis1. Prophase

a. Nuclear membrane, nucleus and nucleolus start to disappear

b. Chromosomes are clearly visible and are randomly arranged

c. Spindle fibers and centrioles appear (not in plants)

2. Metaphase

a. Chromosomes are lined up at the center of the cell (metaphase plate)

b. Done by attaching themselves to the visible spindle fibers

3. Anaphasea. The sister chromatids are pulled apart (at

the centromeres) to the opposite poles of the cell.

b. Each chromatid is a single chromosome.c. Each side gets an exact copy of each

chromosome.

4. Telophasea. Nuclear membrane, nucleus and nucleolus

reappears.

b. Chromosomes and spindle fibers start to disappear.

c. Mitosis is complete at this point.

D. Cytokinesis1. The completion of M phase where cell

organelles and cytoplasm are divided into two new cells.

2. In plant cells the Golgi bodies secrete a cell plate in the middle of the cell.

Mitosis Video Clip

Centrioles

Chromatin

Interphase

Nuclear envelope Chromosomes (paired

chromatids)

Prophase

Centromere

Spindle forming

Metaphase

Centriole

Spindle

Centriole

Anaphase

Individual chromosomes

Nuclear envelope reforming

Telophase

Cytokinesis

DRAW Fig. 10-5, pg. 246

Mitosis Movie

IV. Regulating the Cell Cycle

A. Controls on Cell Division1. When cells come into contact with other cells

they respond by not growing (density dependent inhibition)

2. Controls on cell growth and cell division can be turned on and off

3. With an injury, cells at edge of injury are stimulated to divide rapidly to begin healing

B. Cell Cycle Regulators1. Cyclins are proteins that regulate the cell cycle

2. They signal when it is time for a cell to divide, duplicate their chromosomes, or enter another phase of the cycle

A sample of cytoplasm is removed from a cell in mitosis.

The sample is injected into a second cell in G2 of interphase.

As a result, the second cell enters mitosis.

C. Cancer1. Uncontrolled cell growth and division

2. Cells do not respond to regulatory signals

3. Malignant tumors are masses of cells that can damage surrounding tissue

4. When a cancer metastasizes, cells have broken off the tumor and traveled to other parts of the body

5. Known causes are smoking, tobacco, radiation exposure, and certain viruses

V. Stem CellsA. Three to five days after fertilization, a human

embryo is a mass of cells called stem cellsB. Stem cells are pluripotent, which means

they are not specialized and have the ability to differentiate (develop into any specialized cell, e.g. nerve cell)

C. Three current sources:1.Embryonic stem cells (discarded embryos

from fertility treatment)2.Umbilical cord blood3.Adult stem cells (bone marrow, heart, brain,

lungs)

D. Potential Treatments1.Alzheimer’s disease2.Heart disease3.Limb regeneration4.Organ transplants

http://www.pbs.org/wgbh/nova/sciencenow/3209/04.html