M E I O S I S
M E I O S I S Why don’t cells get bigger forever?? Let’s do a lab! – With some math! Surface area = 6 (l x w) Volume = l x w x h.
Dec 17, 2015
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- Slide 1
- Slide 2
- M E I O S I S
- Slide 3
- Why dont cells get bigger forever?? Lets do a lab! With some math! Surface area = 6 (l x w) Volume = l x w x h
- Slide 4
- Calculations Cell 2 Sides: 1 cm SA= Volume = Cell 1 Sides:.5 cm SA= Volume = Cell 3 Sides: 2 cm SA= Volume =
- Slide 5
- Limits to cell growth The larger a cell becomes, the more demands the cell places on its DNA. In addition, the cell has more trouble moving enough nutrients and wastes across its cell membrane Activity
- Slide 6
- Surface Area to volume ratio We want surface area to be bigger then volume WHY? (Think about the lab)
- Slide 7
- So how do cells solve this problem? Before they get too large They divide! Into two daughter cells Called CELL DIVISION
- Slide 8
- What steps may be involved?steps
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- Two stages Stage 1: MITOSIS Dividing nucleus Stage 2: CYTOKINESIS Dividing cytoplasm
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- Chromosome We have 46! Super condensed DNA In mitosis, each chromosome gets copied Now called two SISTER CHROMATIDS held together by a centromere
- Slide 11
- AnimationAnimation 1 AnimationAnimation 2
- Slide 12
- Sketch it out!
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- The Cell CycleCell Cycle Series of events that cells go through as they grow and divide Grows, prepares to divide, and divides Two main parts Interphase Mitosis
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- Divided into 2 parts Interphase Interphase G 1 - Gap - Cell grows from last cell cycle S Synthesis of DNA (DNA makes a copy of itself) G 2 Cell grows and gets ready for cell division nerve cells that stop dividing at maturity G 0 No cell division typical of cells like nerve cells that stop dividing at maturity Mitosis Mitosis M phase Mitosis Prophase Metaphase Anaphase Telophase Cytokinesis
- Slide 17
- Interphase Longest phase in the Cell Cycle over half the time is spent in this phase
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- Mitosis Prophase Prophase longest phase in Mitosis 1.Copied chromosomes pair up. Held together by Centromere (each is called a chromatid) 2.Shortening up of chromosomes, makes them visible 3.Replicated Centrioles (of animal cells) migrate to opposite poles 4.Nuclear envelope & nucleolus start to break down 5.Spindle fibers (microtubules) extend from centrioles to centromeres
- Slide 19
- Metaphase Metaphase shortest part of Mitosis Chromosomes line up on the equator (middle)
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- Anaphase Anaphase And away they go! Chromatids separate and go to opposite poles. Now called chromosomes!! Spindle fibers shorten up
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- Telophase Telophase the end Final phase Chromosomes reach opposite ends Cell membrane pinches in (cleavage furrow) or Cell plate forms (if plants) Chromosomes uncoil Nuclear membrane & nucleolus reappear Spindle fibers disassembles
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- Cytokinesis Cytokinesis Dividing cellular contents. Occurs simultaneously with Telophase MITOSIS OVERVIEW
- Slide 23
- Difference between Plant and Animal mitosis No centrioles in plant cells A cell plate forms in plant cells
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- Difference between Plant and Animal mitosis Animal cells have a cleavage furrow that splits the two cells
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- How do cells Know when to Found important factors Contact prevents growing grow?
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- Cyclin is a protein that regulates the timing of the cell cycle. Amount of cyclin in a cell rises and falls with the steps in the cell cycle. There are other internal and external proteins that are also involved the cell cycle. Cancer Cancer uncontrolled cell growth. Cells do not respond to normal signals and grow out of control. Cause masses called tumors.
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- Cancer Cancer occurs when cells do not respond to signals that tell them to stop growing
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- Count those chromosomes We have 46 If we made a baby, how many would they have? 46 from mom46 46 from dad + 46 92 for baby No longer human!!
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- What do we do? We go through MEIOSIS Process that takes our two sets of chromosomes (diploid number{2N}) and cuts them into one set (haploid number{1N}) 46 23 23 from mom + 23 from dad = 46! Normal baby!
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- MeiosisMeiosis Steps Unlike mitosis, meiosis has two stages of division Meiosis I Meiosis II
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- Meiosis I: Interphase I: Replication of chromosomes. Like chromosomes are called homologous chromosomes
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- Prophase I: The homologous chromosomes come together (Synapsis) and form a group of 4 called a tetrad. Twisting & exchange parts of adjacent chromatids will occur Crossing over.Crossing over This results in genetic recombination and unlinks genes that are located on the same chromosome. HUGE GENETIC VARIETY!!!!!
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- Anaphase I & Telophase I Chromosomes separate independently of each other. This is known as Independent assortment. Results in Random separation of chromosomes Genetic recombination !!!!!
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- At the end of Meiosis I, there are 2 - 1N cells Meiosis I Results in 2 - 1N cells Meiosis II Results in 4-1N cells
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- Meiosis II Occurs immediately following Telophase I. NO INTERPHASE II !! 1N cells immediately go into Prophase II, then Metaphase II, Anaphase II, and Telophase II Split into four 1N cells, each with unpaired chromosomes Haploid At the end of Meiosis II, there are four 1N cells.
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- Meiosis Animations http://www.sumanasinc.com/w ebcontent/animations/content/ meiosis.html http://www.sumanasinc.com/w ebcontent/animations/content/ meiosis.html John Kryk Cells Alive You Tube http://www.csuchico.edu/~jbell /Biol207/animations/meiosis.ht ml http://www.csuchico.edu/~jbell /Biol207/animations/meiosis.ht ml McGraw Arizona How Mitosis and Meiosis Differ
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- Gametogenesis Creation of gametes (sex cells) Spermatogenesis (testes) Makes 4 haploid sperm cells from 1 - 2N primary sperm cell. Looks like normal Meiosis Oogenesis (ovaries) Oogenesis Produces ovum (eggs) from 1 diploid primary egg cell. Difference occurs during cytokinesis during meiosis I and meiosis II. Unequal distribution of the cytoplasm resulting in 1 large ovum and 3 small polar bodies. Polar bodies serve no function in animals but are needed in to plant embryos.
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- Comparing mitosis and meiosis Be sure to know How many divisions for each? How many starting cells? How many cells at the end? What N are those cells?
- Slide 42
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