since cells can’t continue to grow larger, they must split, or divide at some point
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Since cells can’t continue to grow larger, they must split, or divide at some point. Cell Cycle. 2 parts: Interphase – period of growth & DNA synthesis (copying) Mitotic phase – period of cell division (1 cell divides into 2 cells). I love cells, baby!. - PowerPoint PPT PresentationTRANSCRIPT
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Since cells can’t continue to grow larger, they must split, or divide at
some point.
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Cell Cycle2 parts:• Interphase – period of growth & DNA synthesis
(copying)
• Mitotic phase – period of cell division (1 cell divides into 2 cells)I love cells,
baby!
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Interphase – time of cell growth & copying of DNA
3 phases of interphase:
• G1 – growing & ribosomes making proteins
• S – synthesis (or copying) of DNA (sister chromatids formed)
• G2 – growing & getting ready to divide
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Cells spend most of their time in interphase.
DNA is in chromatin (stringy) form.
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Mitotic Phase – time of cell division
Consists of 2 main phases:1. Mitosis – division of nucleus2. Cytokinesis – division of cytoplasm
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Sister Chromatids
• Identical copies of chromosomes attached by a centromere.
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Mitosis
4 phases:• Prophase • Metaphase• Anaphase• Telophase
http://www.cellsalive.com/mitosis.htm
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Prophase
• DNA condenses into chromosomes
• Nuclear membrane disappears
• Centrioles move toward poles
• Spindle fibers form & attach to chromosomes
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Metaphase
• Sister chromatids lined up on metaphase plate with spindle fibers attached to them.
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Anaphase• Sister chromatids get pulled apart to poles
as spindle fibers shorten.
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Telophase• New nuclear membrane forms around
chromosomes at each pole• Chromosomes “unpack” into chromatin• Cell membrane begins to pinch in (animals cells)
or cell plate develops (plant cells)
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Cytokinesis – division of the cytoplasm
Cleavage furrowCell plate
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Control of the Cell Cycle
• Enzymes control cell cycle so cells divide at the right times
• Cancer – uncontrolled cell division caused by a change in the DNA that codes for the making of the control enzymes
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Cell Cycle Control• http://wps.prenhall.com/esm_freeman_biosci_
1/7/1948/498717.cw/index.html
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Internal Vs external signals
• Internal – the checkpoints
• External – growth factors, density dependent inhibition, anchorage dependence
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Cell cycle checkpoints
• length varies depending on cell type
cell cycle checkpoints control the cell’s progression.
Check points determine if a cell is ready to progress to the next stage. G1 – mostly controlled by growth factors
G2 - determines if cell will enter the M phase & requires proper completion of DNA synthesis. M - b/t metaphase & anaphase; requires the proper attachment of all chromosomes to spindle apparatus.
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MPF = mitotic cyclin dependent kinase complex
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How MPFs work to control the cell cycle
Once bound to cyclin, the mitotic cyclin depdendent kinase complex (or MPF) phosphorylates proteins involved in the early stages of mitosis. The active MPF stimulates the following:
• breakdown of the nuclear envelope• chromosome condensation,• mitotic spindle formation • degradation of key proteins. • activating the anaphase promoting
complex
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To sum up…
• CDKs are only active when bound to cyclin.• When working, they cause the cell to go
through the mechanics of mitosis.• The cell doesn’t continually go through mitosis
b/c the cyclin gets destroyed when the MPF complex reaches a certain concentration.
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cancer
• Tumor• Begign• Malignant• Metastasis• Radiation & chemo
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Cancer
• Forms tumors & can spread through body - metastasize
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Causes of Cancer
• Environmental factors
• UV radiation from sun
• Tobacco• Viral
infections • Genetic
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How to prevent cancer:
• Low fat, high fiber diet
• Vitamins• Exercise• Don’t smoke• Use sunscreen• Regular doctor
appointments
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Removal of colon polyps
• http://www.gihealth.com/flashvideo/flash.html
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Review of the cell
cycle
• http://www.cellsalive.com/mitosis.htm
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2 Basic Modes of Reproduction:
1. Asexual – one parent– Produces offspring ID to parent– Ex: sponges, some worms, some plants,
bacteria, some fungi– Variation occurs through mutation
2. Sexual – two parents– Genetic variation occurs
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Meiosis
• The making of gametes
• Reduces chromosome # by ½ so the 2 halves can come together & make a whole.
• Creates genetic variation.
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Terms you need to know:
• Somatic cell – all cells other than sperm & egg. Humans = 46 chromosomes;diploid ( 2n)
• Gametes – sperm & egg. Humans = 23 haploid (n)
• Gene – seg of DNA that codes for the making of a polypeptide
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Karyotype• An ordered picture of an individuals chromosomes
used to detect abnormal chromosome #
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Trisomy 21 karyotype
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More terms you need to know:
• Homologous chromosomes – paired chromosomes that contain genes that code for the same traits.
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Homologous Chromosomes
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Meiosis has 2 parts:
• Meiosis produces 4 non – identical haploid gametes.
• Meiosis I – separates homologous pairs of chromosomes.
• Meiosis II – separates sister chromatids – just like mitosis.
•http://www.cellsalive.com/meiosis.htm
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Meiosis I & II
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2 Notable events in meiosis I that cause genetic variation in gametes:
1. Random assortment of homologous chromosomes - there are 2 possible arrangement of maternal & paternal chromosomes on the metaphase plate. 2n –
humans = 8 million possible combinations
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2 Notable events in meiosis I that cause genetic variation in gametes …
2. Crossing over – occurs when nonsister chromatids of homologous chromosomes exchange genes. Can happen at up to 3 different locations along the pair.
http://www.csuchico.edu/~jbell/Biol207/animations/recombination.html
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A third notable event that causes variation in offspring, not gametes, &
occurs after meiosis if sperm & egg meet:
• Random fertilizaiton – chance determines which sperm (all of which are different) fertilizes which egg (all of which are different).
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Meiosis & Mitosis compared:
• http://www.pbs.org/wgbh/nova/baby/divi_flash.html
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Mistakes in Meiosis• Nondisjunction – when chromosomes don’t
separate during meiosis.• Results in:• Trisomy – 3 of a chromosome– Ex: Down Syndrome – Ex: Klinefeltersyndrome xxy
• Monosomy – 1 of a particular chromosome– Ex: Turner syn
http://www.tokyo-med.ac.jp/genet/anm/domov.gif
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Trisomy 21
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Some terms
• Autosomes – chromosomes other than the sex chromosomes
• Tetrad• synapsis• chiasmata
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Evolutionary adaptation depends on a
population’s genetic variation.
• Those individuals best adapted to their env will live longer & therefore reproduce more, passing on their well adapted genes.
• More variation means a greater chance of individuals being better adapted, allowing for the survival of the species.
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