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Chapter 10: Cell Growth, Division, and Reproduction Why must a cell divide? a) a large cell places a large demand on the DNA… “info overload” b) a large cell has a low surface area to volume ratio – cell is less efficient at moving materials in and out c) a smaller cell has it’s own DNA – (not overworked anymore) AND a HIGH surface area to volume ratio. Can manage cell needs better Cell Division: 2 Types: Asexual and Sexual Asexual Reproduction: * Offspring are produced by a single parent, without the participation of sperm and egg * offspring are genetic copies of the parent and of each other Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Sexual Reproduction: • Fertilization of sperm and egg produces genetically different offspring • Creates a variety of offspring Why is cell division necessary? • growth • cell replacement • wound repair • asexual reproduction Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Prokaryotes reproduce by binary fission: asexual • As the cell replicates its single chromosome, the copies move apart • The growing membrane then divides the cells Prokaryotic chromosomes Figure 8.3B Colorized TEM 32,500 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings THE EUKARYOTIC CELL CYCLE AND MITOSIS The large, complex chromosomes of eukaryotes duplicate with each cell division LM 600 •A eukaryote has many more genes (and chromosomes) than a prokaryote • Genes are grouped into multiple chromosomes in the nucleus •Each chromosome contains a very long DNA chain with attached histone proteins •Chromosomes are ONLY visible during cell division •If a cell is not undergoing division, chromosomes unwind into loosely packed fibers called chromatin Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 46 chromosomes unwound = 2 meters! The Cell Cycle: Interphase and Mitosis 1. 1. Interphase: All DNA is duplicated and cell parts are made. 3 stages: •G (gap)1: normal cell growth •S (synthesis): all DNA is copied (new set of chromatin is synthesized) •G (gap)2: organelles replicated 2.Mitosis: Duplicated chromosomes are evenly distributed into two daughter nuclei. 4 phases: • Prophase • Metaphase • Anaphase • Telophase Cytokinesis Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The Stages of Mitosis: = centromere Sister chromatids Interphase: G1, S, and G2 Prophase: chromatin condenses, sister chromatids join, nucleolus disappears, centrosomes (centrioles) start to produce spindle fibers and begin migrating to poles, nuclear envelope breaks down, spindles attach to chromosomes, and start moving them to the middle Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The Stages of Mitosis: cont’d Mitosis video Metaphase: chromosome pairs and centromeres are lined up at middle Anaphase: centromeres split, spindles which are attached to chromosomes recoil and split sister chromatids apart, other spindles get longer and poles are pulled farther apart…cell is stretched Telophase and Cytokinesis: chromosomes unwind into chromatin, nuclear envelope and nucleolus form, spindles disappear, microfilaments pinch at center cytokinesis…cytoplasm completely divides (in plants a cell plate is formed)... 2 new cells Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings SUMMARY: Putting it all together Drawings AND Real Pictures Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Cytokinesis differs for plant and animal cells •In animals, cytokinesis occurs by a constriction of the cell (cleavage) •In plants, cell membrane can’t pinch b/c of cell wall. A cell plate forms instead Figure 8.7A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Cell Division Animations • http://media.pearsoncmg.com/bc/bc_campbell_ concepts_5/media/assets/interactivemedia/acti vityshared/ActivityLoader.html?c6e&12&03&8B %20Mitosis%20and%20Cytokinesis%20Animat ion • http://media.pearsoncmg.com/bc/bc_campbell_ concepts_5/media/assets/videos/AnimalMitosis -V.html Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Do all cells divide at the same rate?? NO Fast dividing: intestinal lining, bone marrow, skin, follicle cells Slow dividing: liver, pancreas Non-dividing: nerve and muscle (after about 5 years of age) Q: How is the cell cycle regulated in each type of cell? A: Physical boundaries, Cyclins, and Regulatory Proteins 1. Physical Boundaries Most cells stop dividing once they TOUCH each other ex) cells in a petri dish grow in a single layer and stop once whole surface is covered. Remove some cells, and border cells will divide again to fill the gap. ex) wound boundary cells are stimulated to divide until the space (wound) is healed. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Regulation of Cell Cycle: Cyclins and Regulatory Proteins 2. Cyclins: proteins present in cells ONLY when dividing 3. Regulatory Proteins: used IN and OUT of the cell to stimulate division ex) INternal regulatory proteins: * one type makes sure all chromosomes are made before going further * another type makes sure all spindles are formed before going further ex) EXternal regulatory proteins: direct cells to increase OR decrease RATE of cell division * growth factors – outside chemical signal for cell to start division: vital in embryo development and wound healing * others work as “red lights” to slow down cell division – preventing tumor development Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Cancer: Uncontrolled Cell Division Cancer cells divide excessively; no control system • produce malignant tumors which invade normal cell space, robbing them of nutrients and blood supply • produce own growth factors constant divide signal • divide and live longer than normal cells •Tumor: benign (cells stay put) OR malignant (cells metastasize) •Carcinomas (covering and linings): skin, intestine (colon) •Sarcomas (support tissue): muscle, bone •Leukemia and Lymphoma: blood tissue •Chemotherapy: side effects felt most by fast-dividing cells •ex: hair follicles, intestinal lining, immune cells •Anti-Cancer drugs: all botanical extracts * Taxol: freezes mitotic spindle no division * Vinblastin and Colchicine: stop spindle formation no division Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Q: What causes cancer cell growth ? A: defects (mutations) in the DNA (genes) which code for regulatory proteins How do these defects happen?? 1. chemical exposure (ex: tobacco and cigarette smoke) 2. radiation exposure (ex: x-rays, uv light rays from sun) 3. viruses can disrupt DNA (ex: HPV, HIV) ** Many cancer cells have a mutation in gene “P53” “P53” gene codes for an internal regulatory cell cycle protein at the S of Interphase. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Normal, Programmed, Cell Death?? Apoptosis: pre-programmed, deliberate cell death Process: 1. cell looses fluid and shrinks 2. chromatin breaks down 3. cell membrane distintegrates 4. cell’s neighbors clean up debris and re-use materials Why needed? 1. This is a key role in embryonic development (ie; shape changes) ex: paddle hand ex: tadpole frog ** Too much cell death is linked to certain diseases (Parkinson’s, AIDS) Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CHROMOSOMES Chromosomes: coiled DNA (chromatin) • in humans: 23 pairs 46 in ea. body cell (23 from mom, 23 from dad) • Homologous chromosomes: same #, size, shape, gene location, centromere location (ex: chromosome #1 from mom is homologous to chromosome #1 from dad, etc.) • haploid # = (n) half (23 total): sex cells (egg and sperm) • diploid # = (2n) double (46 total): body cells • Sex cells (23, haploid): 22 autosomes (#1 #22), 1 sex chromosome (#23) • Body cells (46, diploid): 22 pairs of autosomes… (44 total) 1 pair of sex chromosomes (XX) or (XY) • Q: Which cell determines the sex of the offspring; egg or sperm? Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings MEIOSIS: a.k.a. “reduction division” Summary: • Diploid (2n) cell (germ cell) Phases: • Interphase (G1, S, G2) forms cells with (n) nuclei • Two divisions • Used for gamete formation only • Takes much longer than mitosis • Prophase I • Metaphase I • Anaphase I • Telophase I & Cytokinesis • Prophase II • Metaphase II • Anaphase II • Telophase II & Cytokinesis Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Stages of Meiosis Unique features animation Interphase: G1, S, G2 Prophase I: chromatin condenses, sister chromatids join at centromere, synapsis joins homologous pairs of sister chromatids into tetrads, crossing over occurs to shuffle genes, nuclear envelope and nucleolus disappear, centrosomes migrate and grow spindles, tetrads held together by chiasmata (location of crossing over)...NOT centromere Metaphase I: spindles attach to kinetochores and move tetrads to metaphase plate Anaphase I: chiasmata separate (centromeres don’t), spindles recoil, pull homologous pairs apart, each pair of sister chromatids move to opposite pole. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Stages of Meiosis cont’d Meiosis stages video Telophase I and Cytokinesis: cell pinches in middle divide cytoplasm. Each cell (2) has 1 pair of sister chromatids from each original tetrad Prophase II: spindles form again, attach to and start moving sister chromatid pairs to middle Metaphase II: sister chromatid pairs are lined up at metaphase plate Anaphase II: now centromeres divide, spindles recoil and sister chromatids separate Telophase II and Cytokinesis: nucleolus and nuclear envelope appear, cell pinches in middle, divide cytoplasm…4 new daughter cells made, each with (n) number Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Review: A comparison of mitosis and meiosis comparison animation Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Gamete (Sperm) Formation: begins with a 2n body cell Spermatogenesis: production of sperm Spermatogonia: male germ cells (2n) divide by MITOSIS, some undergo meiosis spermatocytes SPERMATOGONIA (2n) Meiosis I Spermatocyte (2n) Spermatocyte (2n) Meiosis II Spermatid (n) Spermatid (n) Spermatid (n) Spermatid (n) sperm sperm maturation sperm sperm Spermatozoa: small, little cytoplasm, flagella • Head with nucleus, midpiece with mitochondria, flagella Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Gamete (Egg) Formation: begins with a 2n body cell Oogenesis: Production of ovum (egg) • Cytokinesis is unequal one LARGE ovum and 3 polar bodies Oogonia: female germ cells (2n) divide by MITOSIS 1o Oocyte only some will undergo meiosis, others will not Oogonium (2n) germ cell mitosis 1o oocyte (2n) 1o oocyte (2n) meiosis I 2ooocyte (2n) polar body (2n) meiosis II Ovum (n) Polar bodies: a waste of DNA in order to get a large egg conservation of cytoplasm: 1 big egg with lots of energy in it’s stored food polar body (n) polar body (n) polar body (n) Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings A female is born with all the primary oocytes ready to go…takes 12+ years for the process to be completed for first egg Q: Why is everyone different? (except identical twins) • Random crossing over of genes during prophase I • Random orientation of chromosomes at metaphase plate • Random fertilization All this leads to many different combinations of chromosomes in eggs and sperm Orientation animation Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Homologous chromosomes carry different versions of genes • homologous chromosomes can bear different versions of a gene at corresponding loci (gene location on chromosome) Brown coat (C); black eyes (E) Figure 8.17B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings White coat (C); pink eyes (e) Alterations of chromosome number and structure Karyotype: a photographic inventory of an individual’s chromosomes • used to detect abnormal chromosome # or abnormal shapes of chromosomes • How is it done?..next slide, please Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Preparation of a karyotype from a blood sample Hypotonic solution Packed red and white blood cells Fixative Stain White blood cells Centrifuge Blood culture 1 A blood Fluid culture is centrifuged to separate the blood cells from the culture fluid. 2 The fluid is discarded, and a hypotonic solution is mixed with the cells. This makes the red blood cells burst. The white blood cells swell but do not burst, and their chromosomes spread out. 3 Another centrifugation step separates the swollen white blood cells. The fluid containing the remnants of the red blood cells is poured off. A fixative (preservative) is mixed with the white blood cells. A drop of the cell suspension is spread on a microscope slide, dried, and stained. Centromere Sister chromosomes 2,600X Pair of homologous chromosomes 4 The slide is viewed with a microscope equipped with a digital camera. A photograph of the chromosomes is entered into a computer, which electronically arranges them by size and shape. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 5 The resulting display is the karyotype. The 46 chromosomes here include 22 pair of autosomes and 2 sex chromosomes, X and Y. Although difficult to discern in the karyotype, each of the chromosomes consists of two sister chromatids lying very close together (see diagram). Accidents during meiosis change the chromosome count • A result of nondisjunction: failure of chromosomes to separate equally • Can lead to trisomy (2n + 1) individual • Trisomy 21 : Down’s Syndrome ( 1 in 700 births; most common) • Trisomy 18, 15, etc… • XYY: Super Male • XXX: Super female • XXY : Klienfelter’s Syndrome • XO: Turner’s Syndrome Trisomy 21 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Possibility of a Down’s baby increases with maternal age Fertilization after nondisjunction in the mother Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Nondisjunction in Meiosis I vs. Meiosis II failure of homologous pairs to separate Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings failure of sister chromatids to separate Polyploidy: Extra Set(s) of Chromosomes • Results when entire set (s) of chromosomes fail to separate (nondisjunction) during meiosis • 2n + n = 3n (Triploid) • 2n + 2n = 4n (Tetraploid) Miscarriage, severe birth defects, or early death • Polyploidy is lethal in humans but is tolerated in plants • Plants can be forced into polyploidy with colchicine • ex. polyploid coffee beans provide more robust flavor Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Alterations of chromosome structure: birth defects and cancer • Deletions, duplications, inversions, and translocations • Occurs during crossing over example Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Bonus Questions: Pick any 2 of your choice 1. What is the full name of a sperm cell? 2. During which phase is non-disjunction of chromosomes most problematic (Meiosis I or Meiosis II)? 3. When a karyotype is made, what is the “n” number of that cell (n, 2n, 3n or 4n)? 4. Name a chemotherapy agent which prohibits spindle formation. 5. What term describes the spread of malignant cancer to other organs in the body? 6. Cancer of the tissues which function as coverings and linings are collectively called? Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings