THE CELL CYCLE HOW DO CELLS DIVIDE?

Introduction – Answer the following questions: How do we grow? What happens if your skin gets burned? What is the difference between asexual and sexual reproduction? What conditions and molecules are necessary for cell division? If you would be a scientist who studies cell division, what kinds of organisms and tools would you need? Watch: https://www.youtube.com/watch?v=Q6ucKWIIFmg

I. WHY DO CELLS DIVIDE? Most living things grow by increasing the number of cells not by increasing the size of cells. Larger cells have two demands on them: “Exchange of materials become inefficient – lack of nutrients and oxygen, too much waste and CO2 – Remember the SA:V ratio of cells

Cell division is also necessary for healing the organisms’ injuries. It provides a way to pass on genetic information to the next generation and with that to upkeep the species. Sexual reproduction is vital for adapting to new environments and avoiding parasites.

II. Cell Division in Prokaryotes Bacterial chromosomes are naked, don’t contain proteins and circular shaped. Bacteria has only one chromosome that doubles before the cell divides. Simple asexual reproduction takes place after DNA replication. Binary fission only splits the cell in half.

Watch: https://www.youtube.com/watch?v=Th4v_Q1iHfY

III. CHROMOSOME STRUCTURE Cells need to supply their entire DNA to the two new cells – DNA replicates than later, it forms chromosomes. Chromosome is a very long DNA molecule and associated proteins, that carry portions of the hereditary information of an organism. Animation on chromosome packaging: http://www.dnalc.org/resources/3d/07-how-dna-is-packaged-basic.html

DNA needs to be tightly packaged before cell division, so it can be evenly divided between the two new cells. First DNA is wrapped around some small round proteins called histones, that wrapped again and again by other proteins like a wrapping paper wraps a present, until we get the linear-shaped chromosome of eukaryotic cells (chromosomes are only X-shaped at certain phases of cell division)

IV. THE CELL CYCLE The cell cycle is a series of events that cells go through as they grow and divide. During the cell cycle the cell grows, prepares for division and divides to form two (or four) daughter cells each of which begins a new cell cycle. http://www.hhmi.org/biointeractive/eukaryotic-cell-cycle-and-cancer – great click and learn on the cell cycle http://www.youtube.com/watch?v=2aVnN4RePyI at 4:20

V. MITOSIS AND CYTOKINESIS The last stage of the cell cycle (M phase) when the DNA of the cell gets evenly divided and the cell splits to produce two new daughter cells each with the same number and type of chromosomes as the parent cells. Mitosis is divided into four phases: Prophase Metaphase Anaphase Telophase http://www.youtube.com/watch?v=Q6ucKWIIFmg http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter11/animations.html# http://www.loci.wisc.edu/outreach/bioclips/CDBio.html

Prophase – The chromatin condenses into chromosomes Prophase – The chromatin condenses into chromosomes. The centrioles separate, a spindle begins to form. The nuclear envelope breaks down. Metaphase – The chromosomes line up across the center of the cell. Each chromosome is connected to a spindle fiber at its centromere. Anaphase – The sister chromatids separate into individual chromosomes and are moved apart.

Telophase – The chromosomes gather at opposite ends of the cell and lose their distinct shapes. Two new nuclear envelopes will form.

The cytoplasm pinches in half The cytoplasm pinches in half. Each daughter cell has an identical set of chromosomes -- cytokinesis.

In most animal cells cytokinesis takes place when the cell membrane pinches in until the cytoplasm is pinched into two equal halves. In most plant cells a cell plate forms midway between the divided nuclei. This cell plate gradually becomes a new cell membrane than the cell wall develops. http://www.youtube.com/watch?v=VGV3fv-uZYI http://www.youtube.com/watch?v=C6hn3sA0ip0 -- great details on the entire process

VI. CONTROL OF CELL DIVISION Cell division is a complex process that needs to be regulated. These regulators determine when and how the cell should divide. External regulators: Proteins, called growth factors produced by other cells, speed up the cell cycle. If the cell touches other cells, the cell cycle slows down – cell density Cells need to be anchored to some solid surface to divide

Internal regulators: Cyclins – proteins that regulate the timing of the cell cycle in eukaryotic cells when their concentration increase and they bind with other proteins called kinases, the cell moves to an other stage of the cell cycle. Checkpoints – During checkpoints, other proteins check the DNA and the health of the cell. (G1, G2 and M) The age of the cell. http://www.learner.org/courses/biology/archive/animations/hires/a_cancer5_h.html http://nobelprize.org/educational/medicine/2001/ To review everything: http://www.youtube.com/watch?v=Q6ucKWIIFmg&NR=1

VI. CANCER – uncontrolled cell division Cancer cells lack normal checkpoints because of mutations Internal and external regulators don’t affect them properly are not inhibited by other cells – form tumors will divide indefinitely. (Cancer cells isolated from a woman in the1950s continue to grow today.)

Tumor Progression 2. Blood vessels feed tumor 3. Tumor cells enter blood and lymph vessels Metastasis 4. Secondary tumors form in other parts of the body 1. Tumor growth http://www.youtube.com/watch?v=LEpTTolebqo Movie clips on cancer, its nature and experiments to treat it (Parts 2 and 6)http://www.pbs.org/wgbh/nova/cancer/program.html http://www.youtube.com/watch?v=HonoQ6mE6dY&feature=related

Treatment of Cancer Surgical removal of tumor – Most effective when tumor is in a defined area Chemotherapy – Medicines that disrupt the process of mitosis in rapidly growing cells Radiation Therapy - High energy gamma radiation is aimed at the growing tumor. This damages the DNA in rapidly dividing cells and helps to destroy the tumor.

VII. CHROMOSOME NUMBER Every species has a specific number of chromosomes. If a cell has two copies of each of these chromosomes the cell is diploid. If a cell has only one copy of its chromosomes, this cell is haploid. Chromosomes that carry the same kinds of genes and are copies of each other are called homologous chromosomes.

In animals and plants most cells that build up the organism are diploid. These cells are called somatic cells Cells that are used for reproduction, like the egg cells and sperm cells are haploid and they are called gametes. Must practice determining chromosome numbers and learn the terms on the last two slides.

II. MEIOSIS Watch: http://www. pbs. org/wgbh/nova/miracle/program II. MEIOSIS Watch: http://www.pbs.org/wgbh/nova/miracle/program.html (watch only parts 1 and 4) Meiosis is a division of the nucleus in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. Meiosis results in four haploid daughter cells that are genetically somewhat different from the parent cells.

Prophase I – Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. The tetrads overlap and exchange some of their genetic material – crossing-over. Metaphase I – Spindle fibers attach to the chromosomes. Chromosomes line up as homologous pairs Anaphase I – The fibers pull the homologous chromosomes toward opposite ends of the cell.

Telophase I and cytokinesis – Nuclear membranes form, the cell separates into two haploid cells. Prophase II – Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell. Metaphase II – The chromosomes line up in a similar way to the metaphase stage of mitosis.

Anaphase II – The sister chromatids separate and move toward opposite ends of the cell. Telophase II and cytokinesis – Meiosis II results in four haploid (N) daughter cells. http://www.sumanasinc.com/webcontent/animations/content/meiosis.html http://www.pbs.org/wgbh/nova/baby/divi_flash.html Meiosis square dance: http://www.youtube.com/watch?v=eaf4j19_3Zg

Crossing over in Prophase I results in great diversity because new genetic variations can result from it.

III. WHY DO CELLS NEED TWO TYPES OF CELL DIVISIONS? Mitosis is used for asexual reproduction in single celled organisms or for growth in multicellular organisms. Human body cells reproduce by mitosis and damaged tissues are also repaired with the help of mitosis. Meiosis is used to form reproductive cells, such as egg and sperm cells and create genetic variety

IV. GAMETE FORMATION In females:

In males:

V. KARYOTYPES The chromosomes from a cell that is in prophase or metaphase of mitosis, can be separated and lined up. This method is used to detect various chromosomal disorders in a dividing cell and frequently used to diagnose various chromosomal abnormalities in fetuses during pregnancy.

VI. CHROMOSOMAL MUTATIONS A mutation is a sudden change in the number or structure of chromosomes or in the DNA due to environmental factors called mutatgens. Chromosomal mutation is a change in the number or structure of chromosomes.

A) Change in the shape of the chromosomes:

B) Change in the number of chromosomes Aneuploidy – one or two chromosomes are added or deleted from the entire set. This is caused by the improper separation of chromatids during mitosis or meiosis (nondisjunction) Polyploidy – additional SETS of chromosomes are added to the cell. In this case the cell becomes 3n, 4n etc.