Vocabulary Terms

• Cell division• Chromatid• Centromere• Interphase • Cell cycle• Mitosis• Prophase• Centriole

• Spindle• Metaphase • Anaphase• Telophase • Cytokinesis• Cyclin• Cancer

10-1 Cell Growth

There are limits to cell growth…

The larger a cell becomes…

• …the more demands the cell places on its DNA

• …and the more trouble the cell has moving nutrients & cell wastes across the cell membrane.

• In eukaryotes, when the cell is small, the info stored in the DNA meets all the cell’s needs. But as a cell increases in size, it usually doesn’t have extra copies of DNA available. An “information crisis” will occur.

• The rate at which food, oxygen and water exchange takes place depends on the surface area of the cell.

• The rate of production of waste products, however, depends on the cell’s volume.

Volume is NOT area

Volume increases more rapidly than surface area as a cell grows in size. Think of a town with a quickly increasing population but only 1 main road!

Daughter Cells• To solve the “info crisis”, before cell division

occurs (while still in interphase), the cell replicates, or copies, all of its DNA. Each daughter cell will get a complete set of information.

• Cell division also solves the problem of increasing size by reducing cell volume. Each daughter cell has an increased ratio of surface area to volume. Now the cell is more efficient.

10-2 Cell Division

Where is DNA

located?1. Inside nucleus2. Arranged as

chromosomes (in mitosis)

ChromosomesIn eukaryotic cells, the genetic info

that is passed from generation to generation is carried by chromosomes.

Chromosomes are made up of DNA and proteins.

The cells of every organism have a specific number of chromosomes.– Fruit flies: 8– Humans: 46– Carrot: 18

Chromosomes (cont’d)

Chromosomes are only visible during cell division- otherwise dispersed in form of chromatin.

Once replicated are in form of “sister” chromatids. They are attached to each other by centromeres. In mitosis, the sisters separate, with one part of the pair going to each cell.

Duplicated Chromosome(Late Interphase):

SisterChromatids

Centromere

The Cell Cycle (the life of a

cell)• During the cell cycle, a cell

–Grows–Prepares for division–Divides to form two daughter

cells–Begins the cell cycle again

Cell Cycle

24 hours

“G” or Growth 1 phase

“S” or DNASynthesis

Growth 2

“M” orMitosisphase

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Events of the Cell Cycle

• G1: phase of activity in which cells do most of their growing. – Cells increase in size– Synthesize new proteins and organelles

• S: chromosomes are replicated and the synthesis of DNA molecules takes place. Now committed to rest of cycle.

• G2: shortest phase, when organelles and molecules of cell division are produced. Ready for M.

• M: mitosis phase

Interphase, Mitosis &

Cytokinesis• Interphase: the cell does its regular jobs of making needed proteins

• Mitosis: the cell nucleus divides

• Cytokinesis: the cytoplasm (or cell juice with cell parts) divides

Interphase• Normal

metabolic activities

• Most commonly viewed state

• DNA= chromatin

Late Interphase• Prepares for mitosis

• DNA doubles=Sister chromatids

• Centrioles double in animals

Why do cells divide by Mitosis?

• Growth & Repair• Reproduction of

single-celled organisms under optimal conditions

• constant environment

AmoebaReproducing

Cells dividing by Mitosis…….

• Identical to original cell

• Same chromosome #

• Identical chromosome makeup

Mitosis• Biologists divide this

process into 4 phases:–Prophase–Metaphase–Anaphase–Telophase

Prophase• First and longest phase (50-

60% of mitosis)• The centrioles separate and

take up position on opposite sides of the nucleus. Centrioles are fanlike microtubular structure that helps separate the chromosomes, which attach to these fibers.

Prophase • Nuclear membrane disappears

• Doubled DNA = condensed (coiled more tightly)

• Un-needed nucleolus disappears

Spindle & spindle fibers: Pull apart the sister chromatids

Metaphase• The chromosomes line up

across the center of the cell.

• Microtubules connect the centromere of each chromosome to the poles of the spindle.

Metaphase• Chromoso

mes line up mid- cell

• Facing inward

• Microtubules conntect centromere to each of the two poles.

Anaphase• The centromeres that join

the sister chromatids split, causing the sister chromatids to separate and become individual chromosomes.

• Chromosomes continue to move until they have separated into two groups near the poles of the spindle.

Anaphase

Plant Anaphase

Telophase• The chromosomes, which were

distinct and condensed, begin to disperse into a tangle of dense material.

• Nuclear envelope re-forms• Spindle begins to break apart• Nucleolus becomes visible in each

daughter cell. Mitosis is complete but cell division has yet to take place.

Telophase

Animal Telophase

Cytokinesis: cell’s cytoplasm divides & splits apart

Cytokinesis• This is division of the

cytoplasm.• Usually occurs at the same

time as telophase.• In animals, cell membrane

draws in until cell is pinched into 2 parts. Each part has its own nucleus and organelles.

• In plants, they need a cell wall, so a cell plate forms between the divided nuclei, and a cell wall begins to appear there.

10-3 Regulating the Cell Cycle

Knowing When to Stop• Suppose you had a paper cut

on your finger. Although the cut may have bled and stung a little, after a few days, it will have disappeared, and your finger would be as good as new.

1. How do you think the body repairs an injury, such as a cut on a finger?2. How long do you think this repair process continues?3. What do you think causes the cells to stop the repair process?

Contact Inhibition

When normal cells come into contact with other cells, they respond by not growing.If cells are removed from the center, the bordering cells will divide to fill.

Cell Cycle Regulators

• Hunt & Kirschner (1980s): cells in mitosis contain protein that when injected into nondividing cell, stimulated mitotic spindle to form.

• Called this protein cyclin.

Contact Inhibition Video

• http://www.youtube.com/watch?v=ILWCweQC7k8

Cyclins• Regulate the timing of the

cell cycle in eukaryotic cells.

• Other regulating proteins also exist.

Internal Regulators• Allow cell cycle to proceed only

when certain processes have happened inside cell

• For example, only after chromosomes are duplicated, cell proceed into M phase.

• Another example is cell waiting in anaphase until all chromosomes are attached to spindle.

External Regulators

• Direct cells to speed up or slow down cell cycle.

• Growth factors speed up (embryonic development, wound healing)

• Cell surface regulators- when one cell touches another, signal given to slow down or stop cycle.

Cancer

• Cancer cells do not obey the ordinary signals that regulate cell growth. As a result, they form masses of cells called tumors that can damage surrounding tissues.

Cancerous cells……...

1. Cycle too fast2. Divide into more

than two cells3. No contact

inhibition• Masses of cells =“tumors”• Benign- not

destructive• Malignant-

potentially lethal