Why do cells Divide?

What did we discover in the cell size lab?

How does your body prepare a wound?

How do you replace all of the skin cells you loose every day?

What happens when Cell division doesn’t happen correctly?

Mitosis!

• When it happens correctly Life is great!– http://www.youtube.com/watch?

v=m73i1Zk8EA0&NR=1

• When Mitosis goes wrong (Cancer)

http://www.youtube.com/watch?v=Hm03rCUODqg&feature=related

Define the following:

Chromosome, Sister Chromatid, Centromere, Cell Cycle. Centriole

What is Cell Division?

• Cell Division is the process of making two identical daughter cells from one parent cell

• Each cell has complete DNA & organelles

• Human Cell Division:

46 chromosomes

46

46

A Chromosome = a little packet of DNA.

You have 46 little packets in each cell

Why do Cells Divide?

• Cells divide because the smaller the cell, the more efficient the transport of necessary molecules into and out of them

• The greater the surface area to volume ratio, the better

The faster oxygen diffuses into your cells, the more ATP you make!

When do Cells Divide?

• Cells divide when an organism:– Needs to grow– Needs to repair itself– Needs to reproduce (prokaryotes only!)

Who does Cell Division?

• All organisms!– Single celled (prokaryotes) or multi-cellular

(eukaryotes)

How does Cell Division Happen?

• Cell Division occurs in a series of predictable phases:– Interphase– Prophase– Metaphase– Anaphase – Telophase– CytokinesisThe term “Mitosis” refers to prophase through

telophase

During Interphase

• Growth occurs… DNA Replicates… DNA is in the form of chromatin

Mitosis: Prophase

• 92 Chromosomes condense and pair up into sister chromatids

• Centrioles go to opposite sides of cell and spindle forms

• Nuclear envelope breaks down

• Chromosomes become attached to spindle

Mitosis: Prophase

Mitosis: Metaphase

• 46 pairs of chromosomes line up across the center of the cell

• Spindle completely attaches to the centromere, a protein at the center of the chromosomes

Mitosis: Anaphase

• Sister chromatid pairs are pulled apart by spindle fibers

• Each side of the cell now has 46 chromosomes

Mitosis: Telophase

• Chromosomes become uncondensed

• Nuclear envelope reforms

• Spindle breaks apart

Cytokinesis

• In animal cells, cells are pinched off to form two cells (like a drawstring)

• In plant cells, a cell plate forms between the two cells, eventually becoming a wall

Quiz….You must show understanding of the process of cell division

You and your partner must show one cell creating two cells and illustrate:

Interphase,Prophase,Metaphase,Anaphase, Telophase

ase and cytokinesis by making chalk drawings!

Drawing must show

Must show 1 cell becoming 2and illustrate important

components in each stage:• Chromatin

• Chromosomes (relative # and location)

• Centrioles

• Spindle fiber

• Centromeres

• Nuclear Membrane (dissapearing and forming)

• Cell Membrane

Regulating Cell Division

How do cells know when it is time to divide?

Internal Regulators

• Each phase (G1, S, G2) in the cell cycle has a “checkpoint” at the end

• Cells cannot continue to the next phase unless requirements are met

• ‘Stop’ and ‘Go’ signals are given by proteins called cyclins

• Q: What is the major requirement to go from S phase to G2?

Regulation Gone Wrong: Cancer

• Cancer Cells do not respond to regulators (growth factor, space, attachment, checkpoints)

• Cancer cells can be immortal, and form a tumor

Cancer Basics

• In benign tumors, the abnormal cells stay at the original site

• Benign tumors are often not harmful

• Malignant tumors impair the function of organs

• Malignant tumors can detach and spread throughout the body (metastasis)

• “Cancer” is malignant

Who Gets Cancer?

• Your risk for cancer is determined by:– Genes– Lifestyle– Environment

• Genes: DNA can contain sections that are irregular and prone to cause inappropriate cell division• Cancer early in life can suggest a genetic cause

Who Gets Cancer?

• Lifestyle: tanning, smoking, drinking, unprotected sex can all raise risk for cancer

• Environment: pollutants in air and water (particles, radiation, etc.) can be inhaled/ingested and cause cancer

What you need to do…Show that you understand how cells

divide• Show your understanding of the important

components of a cell:

• Centromeres/Centrioles (M and M’s)

• spindlefibers (String)

• Chromosomes /Chromotin (Licorice)

• Nuclear Membrane (String)

• You must show understanding in: Interphase , All phases of Mitosis, and

• cytokenisis THIS IS ALL OR NOTHING!!!!