Mitosis and Cancer You will learn: -Reasons Cells Divide -Phases of the Cell Cycle -Abnormal Cell Growth

Some reasons why cells divide? Reproduction Growth Repair

Limits to Cell Growth There are two main reasons why cells divide

Reason #1 The larger a cell becomes, the more demands the cell places on its DNA This is called “DNA Overload”

Understanding DNA Overload In eukaryotic cells, DNA is found in the nucleus of the cell. When a cell is small, the information stored in the DNA is able to meet all the needs of the cell

As the cell increases in size, it usually does not make extra copies of DNA. The cell’s DNA would no longer be able to serve the increasing needs of the growing cell

Reason #2 Food, oxygen, and water enter the cell through its cell membrane. Waste products must leave in the same way. The rate at which this exchange takes place depends on the surface area of the cell, which is the total area of its cell membrane

The rate at which food and oxygen is used up and waste products are produced depends on the cell’s volume If a cell gets too large, it would be difficult to get sufficient amounts of oxygen and nutrients in and waste products out

What is the Cell Cycle? A period where the cell grows, replicates its DNA, and divides into two daughter cells.

Mitosis and Meiosis Mitosis: -division of somatic (body) cells Meiosis -division of gametes (sex cells)

Mitosis Interphase Prophase Metaphase Anaphase Telophase

Interphase (inter = between) The "holding" stage or the stage between two successive cell divisions. ~90 percent of a cell's time in the normal cellular cycle may be spent in interphase.

Interphase (Longest Part of the Cell Cycle) technically not part of mitosis, but it is included in the cell cycle cell is in a resting phase performing cell functions DNA replicates (copies) organelles double in number, to prepare for division

Interphase G1 - (Growth 1) S - (Synthesis) - DNA copies G2 - (Growth 2) - cell prepares for division

G1 Phase (Cell Growth) The cell does most of its growing The cell increases in size New proteins & organelles are synthesized

S Phase (DNA Replication) Chromosomes are replicated and the synthesis in DNA molecules take place Key proteins are also synthesized

G2 Phase (Prep. for Mitosis) Shortest of the 3 phases Many of the organelles and molecules required for cell division are produced

M Phase (Mitosis) The process of cell division begins.

MITOSIS nuclear division number of chromosomes remains the same

Prophase (pro=primary,first) In prophase, the chromatin condenses into discrete chromosomes. The nuclear envelope breaks down and spindles form at opposite "poles" of the cell.

Prophase Key Events Chromatin coils to form visible chromosomes In animal cells, centrioles begin to migrate to opposite poles Spindle forms

What is chromatin? When a cell is "resting" i.e. not dividing, the chromosomes are organized into an entangled structure called chromatin

Prophase Chromosome pair up! Chromosomes thicken and shorten -become visible -2 chromatids joined by a centromere Centrioles move to the opposite sides of the nucleus Nucleolus disappears Nuclear membrane disintegrate

Metaphase (meta is like middle) In metaphase, the chromosomes are aligned at the metaphase plate (a plane that is equally distant from the two spindle poles). 
The spindles form the framework of the dividing cell.

Metaphase Chromosomes meet in the middle! Chromosomes arrange at equator of cell Become attached to spindle fibres by centromeres Homologous chromosomes do not associate

Anaphase ana=upward,back The centromeres divide and the paired chromosomes (sister chromatids) move to opposite ends of the cell.

Anaphase Chromosomes get pulled apart Spindle fibres contract pulling chromatids to the opposite poles of the cell

Telophase (telo=end) In this last stage, two distinct daughter cells are formed after the chromatids have migrated to the opposite poles. Cytokinesis is also occurring at this time.

Telophase Now there are two! Chromosomes uncoil Spindle fibres disintegrate Centrioles replicate Nucleur membrane forms Cell divides

Cytokinesis Cyto =cell Kinesis=movement The cell’s cytoplasm divides at the end of telophase Animals - cell pinches inward Plants - a new cell wall forms between the new cells

Results of Mitosis The cell is the most basic unit of organization In animals… cells-->tissue-->organs-->organ systems -->organisms

The Cell Cycle Proteins called cyclins and enzymes that attach to the cyclins and become activated control the cell cycle

CANCER IS UNCONTROLLED MITOSIS!

What is abnormal cell growth? Also called uncontrolled, rapid cell growth is a central feature of cancer. Virtually every cancer is caused by mutations of DNA Genes that regulate cell division are most susceptible to mutations, which may lead to abnormal cell growth.

Tumors Tumors are abnormal growth of cells Benign tumors are non cancerous and and only grow locally Malignant tumors are cancerous and spread to other areas of the body

Abnormal Cell Growth

Abnormal Cell Growth

Surgical Removal of Tumor

A Large Abdominal Tumor

Body without Tumor

Cancer Occasionally, cells lose control of the cell cycle This results from: failure to produce certain enzymes, the overproduction of enzymes Or the production of enzymes at the wrong time.

Cancer Cancer is a malignant growth resulting from uncontrolled cell division Malignant =dangerous to health; marked by uncontrolled growth

Cancer Cancer is the second leading cause of death in the U.S. Lung, colon, breast, and prostate cancers are the most prevalent types

Causes of cancer Genetics Environmental Factors Cigarette smoke Air and water pollution Exposure to UV radiation However, there are still unknown causes and researchers are working to discover these factors.

Cancer prevention Healthy Lifestyle Low fat, high fiber diet Exercise Not smoking Taking daily vitamins and minerals Carotenoids, Vitamins A, C, E, and calcium

Cancer Cancer is difficult to treat in later stages because the cancer may have spread to vital organs and damaged them beyond repair.