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What is going on? Activating Strategy: Check out this video • Teacher Tube Bacterial Growth - YouTube Cell Division and Reproduction EQ: Why do cells need to divide and reproduce Why would a cell need to divide? • GQ- Can a cell just keep getting bigger and bigger? Think about it: Mr. Whitaker’s classroom supply rule • Has your body changed in the past six months? How did you recognize this change? • Has anyone broken a bone or required stitches? How does your body repair itself? • Cells have to make more of themselves to repair wounds, heal bones, replace worn out cells, and to allow an organism to grow in size. What is cell division? Cell Division- is the process by which a cell divides into 2 new daughter cells • Solves the problem of information overload on cell resources • Increases the surface area to volume ratio so that diffusion can efficiently reach the interior of the cell. What is reproduction? The Cell theory says that all cells come from pre-existing cells. Reproductionthe formation of new individuals from existing individuals. • One of the most important characteristics of living things. • There are two types of reproduction: • Asexual reproduction • Sexual reproduction EQ: What is asexual reproduction? Asexual reproduction – Production of new organisms from a single parent cell or organism. • Does not involve the fusion of nuclei • New organisms are identical to the parent. • Involves both cell division and the replication of the genetic material Parent cell 2 identical daughter cells Examples of Asexual reproduction Some plants can produce plantlets along leaves or stems Bacteria cells reproduce in a process called binary fission. Animals: Eventually the bud will separate from the parent Hydra forming a new individual identical to the first one. EQ: What is the Cell Cycle? Cell Cycle: Is the series of events that cells go through as they grow and divide. There are 4 stages: • G1- cells grow • S- DNA replicates • G2- organelles double • M- mitosis and cytokinesis The cell cycle is a continuous process What are Chromosomes Chromosomes are bundles of Genetic information known as DNA • The chromosome is made up of super condensed chromatin: a complex of DNA and histones (a protein) • The coiling of chromatin into a chromosome allows for the equal division of the DNA during cell division Chromosome structure • Chromatid- one of the two copies of the genetic material of a cell. • Centromereattachment site for the sister chromatids. Holds them together. chromatid Chromosome with two sister chromatids Human Karyotype Cell before it enters the Sphase of the cell cycle Often called the Resting phase 3 phases of cell cycle are in interphase What happens •Cell grows in size- G1 •DNA replicates - S •Organelles double in number- G2 GQ: Why is it important for the DNA to replicate before the cell divides? • So that each new daughter cell will have a complete copy of the DNA Parent cell 2 identical daughter cells Vocabulary closure • Select 2 words from this list. • Make up a definition for these words and write the definition only on the index card. Chromatid Chromosome Centromere Reproduction Cell division Asexual reproduction Chromatin Cell cycle the cell cycle Often called the Resting phase 3 phases of cell cycle are in interphase What happens •Cell grows in size- G1 •DNA replicates - S •Organelles double in number- G2 EQ: What is Mitosis: Mitosis is: • An orderly series of changes in the nucleus • Comes after the exact duplication of the complete set of chromosomes in a cell • Involves the equal separation of these chromosomes into two new nuclei • Each nuclei gets a complete set of chromosomes 4 Stages of Mitosis: What happens •DNA forms chromosomes(Chromosomes Condenses or coils) •Spindle forms •Centrioles move toward opposite poles •Nuclear membrane starts to disappears What happens •Nucleus has disappeared completely •Chromosomes line up in the middle of the cell “equator” What happens •Chromosomes are pulled apart at the centromere by the spindle fibers •The separated Chromatids move to opposite poles What happens •Nuclear membrane forms around each group of chromosomes •Chromosomes uncoil •Cytokinesis begins by the pinching in of the plasma membrane Cytokinesis is: • the separation of the cytoplasm to divide the two new nuclei into separate cells. It starts towards the end of Telophase. • It results in the formation of 2 cells. Plant cell: cell plate formation Animal Cell: Cleavage furrow animal cell vs. plant cell While both animal and plant cells have similar cell cycles and proceed through the same stages of mitosis, there are two significant difference: 1). In cytokinesis: • In animal cells, the plasma membrane pinches in forming a cleavage furrow which form two new cells. • In plant cells, a cell plate forms between the cells. 2). Plant cells do not have centrioles to attach to the spindle fibers. End result of mitosis 1. Two daughter cells are formed 2. Each daughter cell contains the exact kind and number of chromosomes form the parent cell. Animations and Videos of Mitosis • http://www.cellsalive.com/mitosis.htm • http://evanblum.com/school/mitosis.swf • Mitosis (Somatic Cell Division) - YouTube EQ: What is sexual reproduction • Sexual Reproduction: The production of a new organism that involves two parent organisms • Each parent contributes 1/2 of the genetic material for the new individual. • Involves the fusion of nuclei • New individual is NOT identical to either parent Specialized cells from each parent Cell Division in Sexual Reproduction Diploid: 2N means that a cell has two sets of chromosomes. Humans have 23 pairs of chromosomes. The diploid number is 46. Haploid:1N means that a cell has only a single set of chromosomes. Gametes are cells that are haploid Gametogenesis: • process in which gametes are produced • Occurs in the gonads (ovaries, testes) • Results in cells that are haploid. * When gametes (1N) combine a diploid (2N) zygote is formed EQ: What is Meiosis? Meiosis: type of cell division where number of chromosomes are cut in half. Produces 4 haploid cells from one diploid cell. There are two distinct divisions in Meiosis. • Meoisis I • Meosis II Process of Meiosis I Meiosis I: Consists of Interphase, Prophase I, Metaphase I, Anaphase I, and Telophase I. The phases in Meiosis I are similar to those in Mitosis except for a few things: a). In Prophase 1: Synapsis occurs. This is when the matching (homologous) chromosomes join to form a tetrad. What is the importance of Synapsis and tetrad formation? • Tetrads contain 4 sister chromatids called homologous pairs • Allows for exchange of segments between the chromatids by a process called Crossing Over. • Crossing over increases genetic variability. Process of Meiosis I b). Metaphase I: Tetrads line up at the equator c). Anaphase I: • Tetrads separate from each other and move to the poles of the cell. • Occasionally the tetrads do not separate correctly. This is called nondisjunction. Importance of Nondisjunction • Nondisjunction results in an unequal division of the chromosomes. Why might this be a problem? Some gametes will have too many chromosomes, others will not have enough. *Can be a source of disease and syndromes. People with Downs syndrome have an extra chromosome (trisomy 21) Process of Meiosis I d). Telophase I- Nuclear membrane reforms around chromosomes e). Cytokinesis takes place forming two new cells. • note: cross this line off in your notes. • However, the genetic material is not like the parent cell. Process of Meiosis II • The cells produced in the first division now enter a second round of division known as Meiosis II. • NO Chromosome Replication takes place between the end of Meiosis I and the start of Meiosis II. • The phases are similar to mitosis and Meiosis I and are called prophase II, metaphase II, anaphase II, and telophase II. Result of Meiosis • Formation of 4 daughter cells • Each daughter cell is haploid: contains only 1 set of chromosomes Video of Meiosis http://www.youtube.com/watch?v=6xM XKU7JnMQ&feature=related Meiosis in sexual reproduction • Spermatogenesis: 1. in testes, males produce sperm 2. Each sperm contains 23 chromosomes 3. Each sperm is motile • Oogenesis: 1. In ovaries, eggs (ova) are produced 2. 4 cells are produced, only one becomes an egg 3. The three remaining ones are small and degenerate. They are called polar bodies. Karyotype of a gamete produced by meiosis Haploid gamete cell Diploid body cell karyotype Comparison of Mitosis and Meiosis Mitosis Associated with asexual reproduction Meiosis Associated with sexual reproduction Daughter cells are identical to parent cells Daughter cells have half the # of chromosomes as parent. Cells are smaller due to no growth between divisions. Involves 1 cell division Involves 2 cell divisions No exchange (crossing over) Exchange (crossing over) between homologous between homologous chromosomes chromosomes From One Cell to Many THINK ABOUT IT • The human body contains over a 100 Trillion cells all of which came from a single cell, the fertilized egg called the zygote • There are hundreds of different cell types that perform different functions. ex: liver cells, red blood cells, nerve cells http://www.teachersdomain.org/resource/tdc 02.sci.life.cell.stemcellvid/ How do the cells get to be so different from each other? • The process by which cells become specialized is known as differentiation. • Differentiation is controlled by genes, the genetic instructions encoded in the DNA of every cell. • Genes instruct each cell how and when to build the proteins that allow it to create the structures, and perform the functions, specific to its type of cells Stem Cells • Embryonic Stem Cells • Researchers have grown stem cells isolated from human embryos in culture. • Their experiments confirmed that embryonic stem cells have the capacity to produce most cell types in the human body. Stem Cells Adult Stem Cells •Adult organisms contain some types of stem cells. •They can produce many types of differentiated cells. •Adult stem cells of a given organ or tissue typically produce only the types of cells that are unique to that tissue. Cell cycle regulation • There are regulatory proteins that control the cell cycle so that cells do not grow and divide continually when new cells are not needed These proteins are called cyclins • The genes that produce regulatory proteins can be turned on and off like a switch. Ex: p53, Mad1 What happens when the controls fail? When the controls of the cell cycle fail, cell growth and division goes unchecked. Cell Cycle - YouTube • Cancer is a disorder in which body cells lose the ability to control cell growth. • Cancer cells divide uncontrollably to form a mass of cells called a tumor. What Causes Cancer? • Cancers are caused by defects in genes that regulate cell growth and division. Tumor suppressor and oncogenes YouTube • Some sources of gene defects are smoking tobacco, radiation exposure, defective genes, and viral infection. • A damaged or defective p53 gene is common in cancer cells. It causes cells to lose the information needed to respond to growth signals. What is this? Can you describe what is happening in: G1: Cells grow S: Chromosomes replicate or synthesize (why is this phase so important during cellular division?) Cell Cycle G2: Cells grow and organelles double What cell division is used in asexual reproduction? Mitosis Describe the offspring that result from asexual reproduction They are identical to the parent organism. They have the exact same number of chromosomes. What is happening in each phase of Mitosis? ***Interphase is a part of cell cycle, but not a part of mitosis What cell division is used in sexual reproduction? Meiosis Why is meiosis necessary for sexual reproduction? Gametes must be haploid. If not, the organism would end up with too many chromosomes. What is this structure called? Tetrad What is the process called that forms this structure? synapsis When in Meiosis does it occur? prophase I Homologous pairs. One chromosome is from the father, the other matching one in the set is from the mother 1. Synapsis allows for crossing over. When chromosomes synapse, what can happen between the homologous chromosomes? Is this a good thing? 2. This recombination increases the genetic variability of the population. 3. This is usually a good thing as it can help a population to survive in a changing environment. Know what happens in Meiosis 1 and in Meiosis 2 Production of gametes gonads two No change Cut in half. Daughter cells are diploid Gametes are haploid eight two Exactly the same