BIOL 217 W24 Topic 09 (1) PDF

BIOL 217 Topic 09 Fall 2024 Learning Objectives – Topic 09 The Cell Cycle, Mitosis and Meiosis – Chapter 12 & 13 Understand functions of cellular division and the organization of genetic material in chromatin/chromosomes Define key chromosomal/genetic material terminology Understand the...

BIOL 217 Topic 09 Fall 2024 Learning Objectives – Topic 09 The Cell Cycle, Mitosis and Meiosis – Chapter 12 & 13 Understand functions of cellular division and the organization of genetic material in chromatin/chromosomes Define key chromosomal/genetic material terminology Understand the major phases and processes occurring in the cell cycle during mitosis Explain how the mitotic spindle contributes to chromosomal movement in all phases of mitosis Understand the difference between animal and plant cell cytokinesis 2 Learning Objectives – Topic 09 The Cell Cycle, Mitosis and Meiosis – Chapter 12 & 13 Understand why cellular checkpoints are important and what happens when they malfunction Explain how genetic material is passed through generations Understand chromosomal numbers in humans, haploid vs diploid cells (and examples in the body), human life cycle Describe differences between asexual and sexual reproduction Explain the major outcomes of meiosis, major phases of meiosis I and meiosis II, how genetic diversity occurs Compare and contrasts mitosis and meiosis 3 Chapter 12: The Cell Cycle & Mitosis 4  Cellular Division The ability of organisms to produce more of their own kind The continuity of life is based on the reproduction of cells, or cell division Mitosis and Meiosis 5 Figure Page 265  Functions of Cellular Division In unicellular organisms: Division of one cell reproduces the entire organism Multicellular eukaryotes depend on cell division for: Development from a fertilized egg Growth Repair 6 Figure 12.2  Introducing the cell cycle Cell division is an integral part of the cell cycle Cell cycle: the life of a cell from formation to its own division Most cell division results in two daughter cells with identical genetic information The exception is meiosis: A special type of division that can produce sperm and egg cells (gametes) Produces non-identical daughter cells 7 Figure Page 246  Cellular Organization of the Genetic Material Genome: all the DNA in a cell Chromosomes A genome can consist of: A single DNA molecule (common in prokaryotic cells) A number of DNA molecules (common in eukaryotic cells) DNA molecules in a cell are packaged into chromosomes 8 Figure 12.3  Cellular Organization of the Genetic Material Eukaryotic chromosomes consist of chromatin Chromatin: a complex of DNA and protein (histones) that condenses during cell division Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus 9 National Human Genome Research Institute. (n.d.). https://www.genome.gov/sites/default/files/tg/en/illustration/chromatin.jpg  Distribution of Chromosomes During Eukaryotic Cell Division In preparation for cell division, DNA is replicated, and the chromosomes condense Each duplicated chromosome has two sister chromatids Sister chromatids: joined copies of the original chromosome, attached along their lengths by cohesins Cohesins: protein complexes that attach sister chromatids Figure 12.4 10 Figure 13.9  Distribution of Chromosomes During Eukaryotic Cell Division The centromere: The narrow “waist” of the duplicated chromosome Where the two chromatids are most closely attached During cell division, the two sister chromatids separate and move into two new nuclei Once separate, the chromatids are called chromosomes 11 Figure 12.5  The two major phases of the Cell Cycle Interphase (G1, S, and G2) Cell growth and copying of chromosomes in preparation for cell division Mitotic phase (Mitosis and Cytokinesis) Mitosis: the division of the genetic material in the nucleus Cytokinesis: the division of the cytoplasm 12 Figure Page 264  Interphase: G1, S, and G2 Cell growth and copying of chromosomes in preparation for cell division About 90% of cell cycle Cell grows during all three phases, but chromosomes are duplicated only during S phase G1 phase: First gap, cells increase in size, gets ready for S phase S phase: Synthesis, DNA replication occurs G2 phase: Second gap, cells continue to grow, gets ready for Mitosis 13 Figure 12.6  Mitosis consists of 5 stages Page 250-251 in Textbook 14 Figure 12.7  G2 of Interphase A nuclear envelope enclose the nucleus Two centrosomes have formed Regions that organize microtubules Chromosomes duplicated in S phase cannot be seen, because they have not condensed 15 Figure 12.7  Prophase Chromatin fibers tightly coil into discrete chromosomes, becoming visible Duplicated chromosomes appear as two sister chromatids joined at centromeres Mitotic spindle begins to form Centrosomes and the microtubules extending from centrosomes Centrosomes move away from each other 16 Figure 12.7  Prometaphase Nuclear envelope fragments, chromosomes are even more condensed Microtubules from each centrosome invade nuclear area Kinetochore: protein structure at the centromere on each sister chromatid Some microtubule become kinetochore microtubules, jerking chromosomes back and forth Any non kinetochore microtubules elongate the cell 17 Figure 12.7  Metaphase Centrosomes now at opposite poles of the cell Chromosomes have arrived at the metaphase plate An imaginary plane at the middle of the cell Centromeres lie at metaphase plate Kinetochore of each sister chromatid attach to 0 kinetochore microtubules 18 Figure 12.7  Anaphase Shortest phase of mitosis Cohesins between chromatids are cleaved, allowing each pair to separate (becoming an independent chromosome) Two new daughter chromosomes moving towards opposite poles Centromeres lead, because microtubules attached to kinetochore (at centromere) 19 Figure 12.7  Telophase and Cytokinesis Telophase: Two daughter nuclei form Nuclear envelope reappears Chromosomes start to decondense Mitosis is now complete, creating two genetically identical nuclei Cytokinesis: Division of the cytoplasm Involves formation of a cleavage furrow, pinching cell in two (animal cells) 20 Figure 12.7 Animal Cell Mitosis (time-lapse) 21 BioFlix Animation: Mitosis 22  Plant cell cytokinesis in onion root cells 23 Figure 12.11  The Mitotic Spindle: A structure made of microtubules that controls chromosome movement during mitosis In animal cells, assembly of spindle microtubules begins in the centrosome Microtubule-organizing center (MTOC) The centrosome: Replicates during interphase Two centrosomes migrate to opposite ends of the cell during prophase and prometaphase 24 Figure 12.8  The Mitotic Spindle: During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes Kinetochores are protein complexes associated with centromeres At metaphase, the chromosomes are all lined up at the metaphase plate 25 Figure 12.8  The Mitotic Spindle: In anaphase, the cohesins are cleaved by an enzyme called separase Sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell The microtubules shorten by depolymerizing at their kinetochore ends 26 Figure 12.9  The Mitotic Spindle: Non-kinetochore microtubules from opposite poles overlap and push against each other, elongating the cell At the end of anaphase, duplicate groups of chromosomes have arrived at opposite ends of the elongated cell Cytokinesis begins during anaphase or telophase, and the spindle eventually disassembles 27 Figure 12.8  Comparing cytokinesis in animal cell and plant cells In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow Contractile ring of microfilaments In plant cells, a cell plate forms during cytokinesis Vesicles contain cell wall material Vesicles are derived from Golgi apparatus 28 Figure 12.10 Comparing cytokinesis in animal cell and plant cells 29  How do cells know when to divide? Cell Cycle is tightly regulated Some cells divide frequently (intestinal cells) and others rarely divide (neuronal cells) Cancerous cells can escape the usual controls and proliferate 30 https://media.istockphoto.com/photos/traffic-lights-over-urban-intersection-picture-id1168877485?b=1&k=6&m=1168877485&s=170667a&w=0&h=G8brYZiIKsKrvw3cz6Lryxshd-8G0VN5z1hqIh-cTKk=  Molecular clocks The cell cycle is driven by specific chemical signals present in the cytoplasm The cell cycle is directed by a distinct cell cycle control system, which is similar to a clock The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received 31 Figure 12.15  Cellular Checkpoints Changes in regulatory protein concentrations drives the cell cycle Three important checkpoints are those in the G1, G2, and M phases If the cell does not receive the go- ahead signal, it will exit the cycle, Switches to a non-dividing state called the G0 phase 32 Figure 12.17  Cancer cells Have lost their cell cycle checkpoints (due internal and external factors) Can become immortal, continuously divide, provided they have enough nutrients HeLa cells: Harvested from a woman named Henrietta Lacks (in 1951) 33 NIH (2011). https://upload.wikimedia.org/wikipedia/commons/thumb/f/fe/HeLa-V.jpg/1280px-HeLa-V.jpg  34 https://vignette.wikia.nocookie.net/uvmgg/images/d/d3/Karyograms670.jpeg/revision/latest?cb=20121203043439 Chapter 13: Meiosis 35  Meiosis A special type of cell division that can produce sperm and egg cells (gametes) Produces non-identical daughter cells Heredity is the transmission of traits from one generation to the next Variation is demonstrated by the differences in appearance that offspring show from parents and siblings Genetics is the scientific study of heredity and variation 36 Figure Page 270  Inheritance of genetic material Offspring inherit genetic material from parents > genes Genes are the units of heredity and are made up of segments of DNA Locus (plural, loci): A gene’s specific position along a chromosome Genes are passed to the next generation via reproductive cells called gametes (sperm and eggs) 37 National Human Genome Research Institute. https://www.genome.gov/sites/default/files/tg/en/illustration/karyotype.jpg  Inheritance of genetic material Offspring acquire genes from parents by inheriting chromosomes Most DNA is packaged into chromosomes Human somatic cells have 23 pairs of chromosomes (total of 46) Karyotype: an ordered display of the pairs of chromosomes from a cell 38 National Human Genome Research Institute. https://www.genome.gov/sites/default/files/tg/en/illustration/karyotype.jpg  Comparison of Asexual and Sexual Reproduction In asexual reproduction: A single individual passes all of its genes to its offspring without the fusion of gametes A clone is a group of genetically identical individuals from the same parent In sexual reproduction: Two parents give rise to offspring that have unique combinations of genes inherited from the two parents 39 Figure 13.2  Cellular Organization of the Genetic Material Somatic cells : Non-reproductive cells Two sets of chromosomes Diploid Gametes Reproductive cells: sperm and eggs Half as many chromosomes as somatic cells Haploid In an unfertilized egg, the sex chromosome is X In a sperm cell, the sex chromosome may be either X or Y 40 Figure 13.5  Sets of Chromosomes in Human Cell Human somatic cells have 23 pairs of chromosomes The sex chromosomes, are called X and Y Human females have a homologous pair of X chromosomes (XX) Human males have one X and one Y chromosome The remaining 22 pairs of chromosomes are called autosomes Aneuploidy: abnormal number of chromosomes 41 Figure 13.3  Sets of Chromosomes in a Cell The two chromosomes in each pair are called homologous chromosomes, or homologs Chromosomes in a homologous pair are the same length and shape and carry similar genes Each pair of homologous chromosomes includes one chromosome from each parent Non sister chromatids: chromatids in a homologous pair, one from each parent 42 Figure 13.4  Sets of Chromosomes in a Cell The 46 chromosomes in a human somatic cell are two sets of 23 One set from the mother and one set from the father A diploid cell (2n) has two sets of chromosomes For humans, the diploid number is 46 2n = 46 In a cell in which DNA synthesis has occurred, each chromosome is replicated Each replicated chromosome consists of two identical sister chromatids 43 Figure 13.4  Behavior of Chromosome Sets in the Human Life Cycle A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism Fertilization: the union of gametes The fertilized egg is called a zygote Has one set of chromosomes from each parent The zygote produces somatic cells by mitosis and develops into an adult 44 Zebrafish development, Karlstrom and Kane, 1996, Development  Behavior of Chromosome Sets in the Human Life Cycle At sexual maturity, the ovaries and testes produce haploid gametes Gametes are the only types of human cells produced by meiosis, rather than mitosis Meiosis results in one set of chromosomes in each gamete Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number Common to all organisms that reproduce sexually 45 Figure 13.5  Animal life cycles Gametes are the only haploid cells in animals Produced by meiosis and undergo no further cell division before fertilization Gametes fuse to form a diploid zygote that divides by mitosis to develop into a multicellular organism Only diploid cells can undergo meiosis The halving and doubling of chromosomes contributes to genetic variation in offspring 46 Figure 13.6  Meiosis Meiosis reduces the number of chromosome sets from diploid (2n) to haploid (n) Like mitosis, meiosis is preceded by the replication of chromosomes Meiosis takes place in two consecutive cell divisions, called meiosis I and meiosis II Similar steps to mitosis (PMAT) 47 Figure 13.7  Meiosis The two cell divisions result in four daughter cells rather than the two daughter cells in mitosis Each daughter cell has only half as many chromosomes as the parent cell Crossover allows for genetic recombination 48 Figure 13.7 Meiosis 49  Events unique to meiosis, occurring in meiosis I Synapsis and crossing over in prophase I: Homologous chromosomes physically connect and exchange genetic information Create chiasmata Homologous pairs at the metaphase plate Separation of homologs during anaphase I Telophase I creates two haploid cells, each chromosome still consists of two sister chromatids (duplicated chromosomes) 50 Figure 13.8  Meiosis II Meiosis II is very similar to mitosis During another round of cell division, the sister chromatids separate Produces four haploid daughter cells 51 Figure 13.8  Results of Meiosis Chromosomes duplicate before meiosis Pairs of homologs and crossover at chiasma allows for genetic recombination The chromatids are sorted into four haploid daughter cells 52 Figure 13.12 Comparing mitosis and meiosis Mitosis: Conserves the number of chromosome sets Produces cells that are genetically identical to the parent cell Meiosis: Reduces the number of chromosomes sets from two (diploid) to one (haploid) Produces cells that differ genetically from each other and from the parent cell 53  Comparing mitosis and meiosis 54 Figure 13.10  Comparing mitosis and meiosis 55 Figure 13.10