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Cell Growth & DivisionChap 10

II. Cell Size

D. Why does SA/Vol ratio matter so much?

a) Having twice the surface area and the same volume allows for a more efficient exchange of materials. Nutrients, wastes, oxygen, carbon

dioxide and water.

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II. Cell SizeA. Why are cells so tiny?

To maximize the surface area to volume ratio.B. What is the surface area and volume of a

4 cm cube?

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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 x4 x 4 = cm3

SA/V =

96

64

3/2 or 1.5

II. Cell SizeC. What if we cut the cube into eight 2 cm

cubes?

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Volume 2 x 2 x 2 x 8 = cm3

Surface Area 2 x 2 x 6 x 8 = cm2

SA/VOL = cm

192

64

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II. Cell Size

E. Another reason why cells are so small?a) Cell nucleus can only control so much

cytoplasm (the materials inside the cell).

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I. Background InfoA. Why Do Cells Divide?

1. Growth2. Repair damaged cells3. Reproduction

B. Cancer is the result of uncontrolled cell division.

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C. Two parts to cell division (M phase):1. Mitosis - division of nucleus

(DNA); occurs in Eukaryotic somatic (non-reproductive) cells

2. Cytokinesis - duplication and division of the cytoplasm.

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II. ChromosomesA. Prior to division cells must duplicate

their DNA. Why?

1. Chromosomes (DNA) carry all the genetic information for the organism.

2. Chromosomes are made up of chromatina)Chromatin is made of DNA twisted

around histone proteins.b)Chromatin coils to form a

chromatid. Why coil DNA?

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Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

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III. The Cell CycleA.Consists of mitosis (cell division)

and interphase

M phase

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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 (1st growing) phase - cell growth;

right after cell division.b)S (synthesis) phase - DNA replication

(see chp. 7)c)G2 (2nd growing) phase - replication of

cell organelles (to prepare for division) and synthesis of cell division structures.

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The Cell Cycle (Fig. 10-4)

Remember I P M A T

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Cell Cycle Introduction

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IV. Stages of MitosisA. Prophase

1. Nuclear membrane, nucleus and nucleolus start to disappear

2. Spindle fibers and centrioles appear

a)Plant cells don’t have centrioles

3. Chromosomes are clearly visible and are randomly arranged

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B. Metaphase

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

a)Done by attaching themselves to the visible spindle fibers

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C. Anaphase

1. The chromosomes are pulled (at the centromeres) to the opposite poles of the cell.

2. Each chromosome now is a single chromatid.

3. Each side get an exact copy of each chromosome

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D. Telophase1. Nuclear membrane, nucleus and

nucleolus reappears.2. Chromosomes and spindle fibers

start to disappear.3. Mitosis is complete at this point

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Draw Fig. 10-5 of Mitosis (page 246-247)

Mitosis Movie

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V. Cytokinesis A. Cytokinesis is the division of

cellular organelles & cytoplasm.

B. In plants the Golgi bodies secrete a cell plate in the middle of the cell.

Cell Plate

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VI Regulating the Cell Cycle

• In multicellular organisms, cell growth and cell division are highly regulated… some cells divide often (Skin and bone marrow cells) and others not at all (Nerve cells)

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Cell Cycle Regulators

• In the 1980s researchers discovered a group of proteins that when injected into a cell would initiate cell divisions

• Cyclins regulate the timing of the cell cycle in eukaryotic organisms

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Internal and External Regulators

• Internal regulators monitor events happening inside the cell and allow the cell to progress through the cell cycle

• External regulators respond to events outside the cell and are especially important during embryonic development

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VII Uncontrolled Cell Growth

• Uncontrolled cell growth is Cancer• A mass of cells resulting from uncontrolled cell

growth results in a tumor that may or may not effect surrounding tissue

• The p53 gene codes for a protein that halts the cell cycle until all chromosomes have been replicated

• Dysfunctional p53 genes are found in most types of cancer

Genetic Basis of Cancer