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Cellular Reproduction • Cell division in eukaryotes enables asexual reproduction Copyright © 2005 Pearson Prentice Hall, (F11.1 p. 186) Cellular Reproduction cell division Prokaryotic Cell Cycle: Growth & Binary Fission (F11.2 p187) attachment site cell wall plasma membrane cell growth and DNA replication circular DNA The circular DNA double helix is attached to the plasma membrane at one point. The parent cell divides into two daughter cells. The DNA replicates and the two DNA double helices attach to the plasma membrane at nearby points. New plasma membrane is added between the attachment points, pushing them further apart. Copyright © 2005 Pearson Prentice Hall, The plasma membrane grows inward at the middle of the cell. Cellular Reproduction telophase and cytokinesis G1: cell growth and differentiation G0: nondividing G2: cell growth Eukaryotic Cell Cycle: •Interphase •Cell Division p. Pearson 188) Copyright (F11.3 © 2005 Prentice Hall, interphase S: synthesis of DNA; chromosomes are duplicated Interphase: Cell Grows in Size Replicates Its DNA DNA in Eukaryotic Cells Is Organized into Chromosomes • Eukaryotic Chromosome = 1 Linear DNA Double Helix Bound to Proteins – – – – Chromosome structure Human chromosomes during mitosis (Duplicated) REPLICATED chromosome Daughter chromosomes Copyright © 2005 Pearson Prentice Hall, (F11.5 p. 190) (F11.6 p. 191) (F2 p. 191) (F3 p. 191) DNA (2 nm diameter) histone proteins nucleosome: DNA wrapped around histone proteins (10 nm diameter) coiled nucleosomes (30 nm diameter) chromosome: coils gathered onto protein protein scaffold scaffold (200 nm diameter) DNA coils Copyright © 2005 Pearson Prentice Hall, sister chromatids Copyright © 2005 Pearson Prentice Hall, centromere genes centromere telomeres Copyright © 2005 Pearson Prentice Hall, independent daughter chromosomes, each with one identical DNA double helix sister chromatids Copyright © 2005 Pearson Prentice Hall, duplicated chromosome (2 DNA double helices) DNA in Eukaryotic Cells Is Organized into Chromosomes • Eukaryotic Chromosomes: – Usually Occur in Homologous Pairs • 1 from Mom & 1 from Dad – Homologs Have Similar (NOT IDENTICAL) Genetic Information • Some from Mom & Some from Dad – Karyotype of a human male Copyright © 2005 Pearson Prentice Hall, (F11.7 p. 191) Copyright © 2005 Pearson Prentice Hall, Cellular Reproduction • Two Types of Eukaryotic Cell Division : – Mitotic Cell Division – Meiotic Cell Division • Figure 11.4 (Hide/Reveal) Mitotic and meiotic cell division in the human life cycle (p. 189) • Unnumbered Figure 1 Chromosome (p. 190) Copyright © 2005 Pearson Prentice Hall, Mitotic Cell Division • Mitotic cell division in an animal cell Copyright © 2005 Pearson Prentice Hall, (F11.8 p. 192) INTERPHASE nuclear envelope MITOSIS chromatin nucleolus centriole pairs LATE INTERPHASE Duplicated chromosomes in relaxed state; duplicated centrioles remain clustered. condensing chromosomes pole beginning of spindle formation pole EARLY PROPHASE Chromosomes condense and shorten; spindle microtubules begin to form between separating centriole pairs. Copyright © 2005 Pearson Prentice Hall, spindle microtubules kinetochore LATE PROPHASE Nucleolus disappears; nuclear envelope breaks down; spindle microtubules attach to the kinetochore of each sister chromatid. METAPHASE Kinetochores interact; spindle microtubules line up chromosomes at cell's equator. "free" spindle fibers chromosomes extending ANAPHASE Sister chromatids separate and move to opposite poles of the cell; spindle microtubules push poles apart. INTERPHASE nuclear envelope re-forming TELOPHASE One set of chromosomes reaches each pole and relaxes into extended state; nuclear envelopes start to form around each set; spindle microtubules begin to disappear. Copyright © 2005 Pearson Prentice Hall, CYTOKINESIS Cell divides in two; each daughter cell receives one nucleus and about half of the cytoplasm. INTERPHASE OF DAUGHTER CELLS Spindles disappear, intact nuclear envelopes form, chromosomes extend completely, and the nucleolus reappears. Finn Dorset ewe donor cell from udder electric pulsefused cells Cells from the udder of a Finn Dorset ewe are grown in culture with low nutrient levels. The starved cells stop dividing and enter the non-dividing G0 phase of the cell cycle. Blackface ewe egg cell Meanwhile, the nucleus is sucked out of an unfertilized egg cell taken from a Scottish Blackface ewe. This egg will provide cytoplasm and organelles but no chromosomes. Copyright © 2005 Pearson Prentice Hall, nucleus is removed DNA The egg cell without a nucleus and the quiescent udder cell are placed side by side in a culture dish. An electric pulse stimulates the cells to fuse and initiates mitot cell division. The cell divides, forming an embryo that consists of a hollow ball of cells. The ball of cells is implanted The Blackface ewe gives into the uterus of another birth to Dolly, a female Blackface ewe. Finn Dorset lamb, a genetic twin of the Finn Dorset ewe. Copyright © 2005 Pearson Prentice Hall, Mitotic Cell Division • Prophase – Chromosomes Condense, Spindle Microtubules Form & Attach to the Chromosomes • Metaphase – Chromosomes Align Along the Equator of the Cell • Anaphase – Sister Chromatids Separate & Pulled to Opposite Poles of the Cell • Telophase – Nuclear Envelopes Form Around Both Groups of Chromosomes • Cytokinesis – Cytoplasm Is Divided Between Two Daughter Cells – Cytokinesis in an animal cell (F11.9 p. 197) – Cytokinesis in a plant cell (F11.10 p. 197) Copyright © 2005 Pearson Prentice Hall, Microfilaments form a ring around the cell's equator. The microfilament ring contracts, pinching in the cell's “waist.” Copyright © 2005 Pearson Prentice Hall, The waist completely pinches off, forming two daughter cells. Golgi complex cell wall plasma membrane carbohydratefilled vesicles Carbohydratefilled vesicles bud off the Golgi complex and move to the equator of the cell. Copyright © 2005 Pearson Prentice Hall, Vesicles fuse to form a new cell wall (red) and plasma membrane (yellow) between daughter cells. Complete separation of daughter cells. Cellular Reproduction • Two Types of Eukaryotic Cell Division : – Mitotic Cell Division – Meiotic Cell Division • Mitotic & meiotic cell division in human life cycle (F11.4 p. 189) Copyright © 2005 Pearson Prentice Hall, mitosis, differentiation, and growth mitosis, differentiation, and growth baby meiosis in ovaries embryo mitosis, differentiation, and growth adults egg fertilized egg fertilization Copyright © 2005 Pearson Prentice Hall, sperm meiosis in testes gene 1 same alleles Copyright © 2005 Pearson Prentice Hall, gene 2 different allele sister chromatids homologous chromosomes Copyright © 2005 Pearson Prentice©Hall, Copyright 2005 Pearson Prentice Hall, Meiotic Cell Division Produces Haploid Cells • Meiosis Separates Homologous Chromosomes, Producing Haploid Daughter Nuclei • Meiotic Cell Division Followed by Fusion of Gametes Keeps the Chromosome Number Constant from Generation to Generation • Meiosis I Separates Homologous Chromosomes into Two Haploid Daughter Nuclei – During Prophase I, Homologous Chromosomes Pair Up and Exchange DNA • Homologous chromosomes (F5 p. 198) • • • • Two daughter nuclei Four haploid cells Meiotic cell division Meiotic cell division in an animal cell Copyright © 2005 Pearson Prentice Hall, (F6 p. 198) (F 7 p. 199) (F8 p. 199) (F11.11 p. 200) Copyright © 2005 Pearson Prentice Hall, Copyright © 2005 Pearson Prentice Hall, n 2n meiotic cell division 2n 2n n Copyright © 2005 Pearson Prentice Hall, fertilization MEIOSIS I paired homologous chromosomes chiasma recombined chromosomes spindle microtubule Copyright © 2005 Pearson Prentice Hall, MEIOSIS I paired homologous chromosomes chiasma recombined chromosomes spindle microtubule Prophase I. Duplicated chromosomes condense. Homologous chromosomes pair up and chiasmata occur as chromatids of homologues exchange parts. The nuclear envelope disintegrates, and spindle microtubules form. Metaphase I. Paired homologous chromosomes line up along the equator of the cell. One homologue of each pair faces each pole of the cell and attaches to spindle microtubules via its kinetochore (blue). Copyright © 2005 Pearson Prentice Hall, Anaphase I. Homologues separate, one member of each pair going to each pole of the cell. Sister chromatids do not separate. Telophase I. Spindle microtubules disappear. Two clusters of chromosomes have formed, each containing one member of each pair of homologues. The daughter nuclei are therefore haploid. Cytokines commonly occurs at this stage. There is little or no interphase between meiosis I and meiosis II MEIOSIS II Prophase II. If chromosomes have relaxed after telophase I, they recondense. Spindle microtubules re-form and attach to the sister chromatids. Metaphase II. Chromosomes line up along the equator, with sister chromatids of each chromosome attached to spindle microtubules that lead to opposite poles. Copyright © 2005 Pearson Prentice Hall, Anaphase II. Chromatids separate into independent daughter chromosomes, one former chromatid moving toward each pole. Telophase II. Chromosomes finish moving to opposite poles. Nuclear envelopes re-form, and the chromosomes become extended again (not shown here). Four haploid cells. Cytokinesis results in four haploid cells, each containing one member of each pair of homologous chromosomes (shown here in condensed state). Meiotic Cell Division Produces Haploid Cells • Meiosis I – – – – Metaphase I, Paired Homologs Line Up at the Equator of the Cell Anaphase I, Homologs Separate Telophase I, Two Haploid Clusters of Duplicated Chromosomes Form Mitosis, Meiosis I (F9, 10 p. 202) • Meiosis II Separates Sister Chromatids into Four Daughter Nuclei – The mechanism of crossing over (F11.12p. 200) – Comparison of Animal Cell Mitotic & Meiotic Cell Divisions (T11.1 p. 203) – Chromosome configurations at metaphase I F11 Copyright © 2005 Pearson Prentice Hall, sister chromatids of one duplicated homologue protein strands joining duplicated chromosomes direction of “zipper” formation pair of homologous, duplicated chromosomes Duplicated homologous chromosomes pair up side by side. recombinatio n enzymes Protein strands “zip” the homologous chromosomes together. Copyright © 2005 Pearson Prentice Hall, Recombination enzymes bind to the joined chromosomes. chiasma Recombination enzymes snip chromatids apart and reattach the free ends. Chiasmata (the sites of crossing over) form when one end of the paternal chromatid (yellow) attaches to the other end of a maternal chromatid (purple). chiasma Recombination enzymes and protein zippers leave. Chiasmata remain, helping to hold homologous chromosomes together. duplicated chromosomes Copyright © 2005 Pearson Prentice Hall, spindle microtubules Copyright © 2005 Pearson Prentice Hall, Why Do So Many Organisms Reproduce Sexually? • Mutations in DNA Are the Ultimate Source of Genetic Variability • Sexual Reproduction May Combine Different Parental Alleles in a Single Offspring Copyright © 2005 Pearson Prentice Hall, How Do Meiosis & Sexual Reproduction Produce Genetic Variability? • Shuffling of Homologues Creates Novel Combinations of Chromosomes • Crossing Over Creates Chromosomes with Novel Combinations of Genes • Fusion of Gametes Adds Further Genetic Variability to the Offspring Copyright © 2005 Pearson Prentice Hall, duplicated chromosomes Copyright © 2005 Pearson Prentice Hall, spindle microtubules Copyright © 2005 Pearson Prentice Hall,