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THE CELL CYCLE. HOW DO CELLS DIVIDE?. Introduction – Answer the following questions:. Why do cells divide? ( Try to come up with multiple explanations) What is the difference between asexual and sexual reproduction? What conditions and molecules are necessary for cell division? - PowerPoint PPT Presentation
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THE CELL CYCLE
HOW DO CELLS DIVIDE?
Introduction – Answer the following questions:1. Why do cells divide? (Try to come up with
multiple explanations)2. What is the difference between asexual
and sexual reproduction?3. What conditions and molecules are
necessary for cell division?4. If you would be a scientist who studies
cell division, what kinds of organisms and tools would you need?
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:“Information crisis” – DNA is not able to fulfill
the demands for information in larger cells (not able to give enough information for protein synthesis)
Exchange of materials become inefficient – lack of nutrients and oxygen, too much waste and CO2
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.
http://www.pbs.org/wgbh/nova/miracle/program.html (watch only parts 1 and 4)
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.
III. CHROMOSOME STRUCTURE
Cells need to supply their entire DNA to the two new cells – DNA replicates than 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 non-histone proteins like a wrapping paper wraps a present, until we get the X-shaped chromosome of eukaryotic cells.
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.cellsalive.com/cell_cycle.htm http://www.youtube.com/watch?v=2aVnN4RePyI at 4:20
IV. THE CELL CYCLE
V. MITOSIS AND CYTOKINESISThe last stage of the cell cycle when the
nucleus of a cell divides to produce two new daughter cells (with cytokinesis) each with the same amount and type of chromosomes as the parent cells.
Mitosis is divided into four phases:ProphaseMetaphaseAnaphaseTelophase
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. 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. 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 or slow down 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
mutationsInternal and external regulators don’t
affect them properlyare not inhibited by other cells – form
tumorswill divide indefinitely. (Cancer cells
isolated from a woman in the1950s continue to grow today.)
Tumor Progression
1. Tumor growth 2. Blood vessels feed tumor
3. Tumor cells enter blood and lymph vesselsMetastasis
4. Secondary tumors form in other parts of the body
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 NUMBEREvery species has a determined number
of chromosomes. If a cell has two sets of these chromosomes the cell is diploid.
If a cell has only one set of its chromosomes, this cell is haploid.
Chromosomes that carry the same kinds of genes are called homologous chromosomes.
VIII. MEIOSISMeiosis 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.
IX. 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
X. GAMETE FORMATION
In females:
In males:
X. 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.
XI. MUTATIONS
A mutation is a sudden change in the number or structure of chromosomes or in a small section of the chromosome.
We are going to further organize all types of mutation on a concept map and take separate notes on them. If you miss this section, you need to get the notes from somebody in your class.