L2-L3. The Cell Types and Division PDF

THE CELL: TYPES AND DIVISION JAIRA ANGELINE T. BALISI Department of Environmental Science College of Science Tarlac State University Prokaryotic VS Eukaryotic Cells  Prokaryotic VS Eukaryotic Cells Eukaryotic - subdivided by internal membranes into vario...

THE CELL: TYPES AND DIVISION JAIRA ANGELINE T. BALISI Department of Environmental Science College of Science Tarlac State University Prokaryotic VS Eukaryotic Cells  Prokaryotic VS Eukaryotic Cells Eukaryotic - subdivided by internal membranes into various membrane- enclosed organelles (E.g., chloroplast). Prokaryotic - simpler and smaller; the DNA is separated from the rest of the cell by enclosure in a membrane-bounded nucleus, but lack the other kinds of membrane- enclosed organelles (Campbell, 2005) Eukaryotic: Plant VS Animal Cells PLANT VS. ANIMAL CELL Both Eukaryotic Cells Animal cells are mostly round and irregular in shape while plant cells have fixed, rectangular shapes Plants = Plasmodesmata, Chloroplast, Cell Wall, and Plastids Animal = centrioles, centrosomes, and lysosomes CELL DIVISION OBJECTIVES At the end of the activity, the students should be able to: Describe the sequential changes taking place in the different stages of mitosis and meiosis; Identify the different stages and parts involved in the process of mitosis and meiosis; and Construct thread models of stages of cell division CELL DIVISION  CELL DIVISION Eukaryotic Cell division is the process by which cells replicate to grow, replace cell loss, repair tissue damage (MITOSIS) and reproduce the organism (MEIOSIS). EUKARYOTIC CELL CYCLE 2 Major Phases: Interphase (3 stages) - DNA is not condensed Cell Division: - Nuclear division & division of cytoplasm - DNA condensed The timing of replication and cell division is highly regulated.  INTERPHASE Non-dividing state with 4 sub-stages: Gap 0 (G0): sometime cell will leave the cycle and quit dividing. This may be a temporary resting period or more permanent (E.g., neuron). Gap 1 (G1): Cells increase in size, produces RNA and synthesize protein, which are important cell cycle control mechanism activated during this period to ensures that everything is ready for DNA synthesis (like a checkpoint).  INTERPHASE Non-dividing state with 4 sub-stages: S Phase: complete DNA instructions in the cell is duplicated. Gap 2 (G2): the cell will continue to grow and produce new proteins (another Checkpoint) to determine if the cell can now proceed to enter M (mitosis) and divide. MITOSIS MITOSIS two genetically identical daughter cells are produced from the original cell, which are identical structurally and in genetic content. All cells of the body except for the fully differentiated nerve cells undergo mitotic division. Sub phases: Prophase, Metaphase, Anaphase, Telophase Followed by: Cytokinesis  PROPHASE the start of prophase is marked by the condensation of chromatin to form visibly distinct chromosomes. The chromosome is made up of two sister chromatids joined at the centromere. the nuclear membrane disintegrates, the nucleolus disappears and mitotic spindle forms. Animal cell Plant cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm  METAPHASE (ANIMALS) Chromosomes line up along the metaphase plate, a plane that lies between the spindle poles. Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm  METAPHASE (PLANTS) Chromosomes align along the equator of the cell, with one chromatid facing each pole Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm  ANAPHASE centromeres divide and the two sister chromatids move toward the opposite poles of the spindle. The movement results from a pulling to the poles by the spindle fibers that are attached to the centromeres. Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm  ANAPHASE Sister chromatids separate Spindle fibers attached to kinetochores shorten and pull chromatids towards the poles. Free spindle fibers lengthen and push the poles of the cell apart  TELOPHASE starts when the chromosomes reach their spindle poles. The chromosomes complete uncoiling, the spindle apparatus is dismantled, nucleolus reappears and nuclear envelope form around each chromosome cluster. Telophase is completed when cytokinesis has taken place, and two daughter cells are produced.  TELOPHASE Spindle fibers disintegrate Nuclear envelopes form around both groups of chromosomes Chromosomes revert to their extended state cytokinesis occurs, enclosing each daughter nucleus into a separate cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm  CYTOKINESIS Division of the cytoplasm. In animal cells, cytokinesis starts with a cleavage furrow or indentation around the middle that eventually pinches in, dividing the cell into two while on the plant cell is the formation of cell plate. Plant cells undergo cytokinesis by Animal cells undergo cytokinesis through the formation of a cleavage furrow. A ring forming a cell plate between the two of microtubules contract, pinching the cell daughter nuclei. in half.  CYTOKINESIS The actual splitting of the daughter cells into two separate cells is called cytokinesis and occurs differently in both plant and animal cells. Beginning of cytokinesis in a plants Beginning of cytokinesis in a animals  REMEMBER! Interphase Prophase Metaphase Anaphase IPMATC Telophase Cytokinesis I Pray More At The Church MEIOSIS  MEIOSIS two genetically none identical daughter cells are produced from the mother cell that occurs in reproductive cells (Germ cells). In humans: Male germ cell = Spermatozoon; female germ cell = the Ovum. Union of germ cells (fertilization) results in the formation of a new organism.  MEIOSIS Genetics Terminology: Ploidy Refers to the number of sets of chromosomes in cells. Haploid – one copy of each chromosome – designated as “n”, the number of chromosomes in one “set” – gametes Diploid – two sets of chromosomes (two of each chromosome) – designated as “2n” – somatic cells Diploid organisms receive one of each type of chromosome from female parent (maternal chromosomes) and one of each type of chromosome from male parent (paternal chromosomes)  INTERPHASE Meiosis is preceded by The chromosomes have interphase. The replicated, and the chromosomes have not yet chromatin begins to condensed. condense.  PROPHASE I Unlike mitosis, the homologous chromosomes pair with one another. At the start of Prophase I, the chromosomes have already duplicated. During prophase I, they coil and become shorter and thicker and visible under the light microscope. The duplicated homologous chromosomes pair, and crossing-over (the physical exchange of chromosome parts) occurs. It can be further divided into five sub- phases: leptotene, zygotene, pachytene, diplotene, and diakinesis.  PROPHASE I The nucleolus disappears during prophase I. In the cytoplasm, the meiotic spindle, consisting of microtubules and other proteins, forms between the two pairs of centrioles as they migrate to opposite poles of the cell. Crossing-over is the process that can give rise to genetic recombination. At this point, each homologous chromosome pair is visible as a bivalent (tetrad), a tight grouping of two chromosomes, each consisting of two sister chromatids.  PROPHASE I (1) leptotene - chromosomes align and prepare for recombination; (2) zygotene - crossing over takes place between the chromatids in the tetrad (crisscrossed non-sister) = chismata (pl) / chiasma (s); (3) pachytene - chromosomes now start to separate; (4) Diplotene - chiasmata break down, and the pairs move apart, and finally diakinesis where they are at opposite poles of the cell. The nuclear envelope disappears at the end of prophase I, allowing the spindle to enter the nucleus. Prophase I is the longest phase of meiosis, typically consuming 90% of the time for the two divisions.  METAPHASE I The nuclear membrane dissolves and the homologous chromosomes attach to the spindle fibers. They are preparing to go to opposite poles.  METAPHASE I The centrioles are at opposite poles of the cell. The pairs of homologous chromosomes (the bivalents), now as tightly coiled and condensed as they will be in meiosis, become arranged on a plane equidistant from the poles called the metaphase plate. Spindle fibers from one pole of the cell attach to one chromosome of each pair (seen as sister chromatids), and spindle fibers from the opposite pole attach to the homologous chromosome (again, seen as sister chromatids). ANAPHASE I Bivalent chromosomes disjoin and each member migrates randomly to opposite poles of the cell. This is the stage at which random and independent assortment of paternal and maternal chromosomes occurs. ANAPHASE I two chromosomes of each bivalent (tetrad) separate and start moving toward opposite poles of the cell because of the action of the spindle. sister chromatids remain attached at their centromeres and move together toward the poles. A key difference between mitosis and meiosis is that sister chromatids remain joined after metaphase in meiosis I, whereas in mitosis they separate. TELOPHASE I & CYTOKINESIS I The cell begins to divide into two daughter cells. It is important to understand that each daughter cell can get any combination of maternal and paternal chromosomes.  TELOPHASE I & CYTOKINESIS I The homologous chromosome pairs complete their migration to the two poles as a result of the action of the spindle. Now a haploid set of chromosomes is at each pole, with each chromosome still having two chromatids. A nuclear envelope reforms around each chromosome set, the spindle disappears, and cytokinesis follows. In animal cells, cytokinesis involves the formation of a cleavage furrow, resulting in the pinching of the cell into two cells. After cytokinesis, each of the two progeny cells has a nucleus with a haploid set of replicated chromosomes. Many cells that undergo rapid meiosis do not decondense the chromosomes at the end of telophase I. Other cells do exhibit chromosome decondensation at this time; the chromosomes recondense in prophase II PROPHASE II The cell has divided into two daughter cells. The chromosomes coil up, the nuclear membrane begins to disintegrate, and the centrosomes begin moving apart.  PROPHASE II A spindle apparatus forms, and the chromosome progresses towards the metaphase II plate.  METAPHASE II As in Meiosis I, the chromosomes line up on the spindle fibers. METAPHASE II Each of the daughter cells completes the formation of a spindle apparatus. Single chromosomes align on the metaphase plate, much as chromosomes do in mitosis. This is in contrast to metaphase I, in which homologous pairs of chromosomes align on the metaphase plate. For each chromosome, the kinetochores of the sister chromatids face the opposite poles, and each is attached to a kinetochore microtubule coming from that pole. ANAPHASE II The two cells each begin to divide. As in Meiosis I, the chromosomes move to opposite ends of each cell. ANAPHASE II The centromeres separate, and the two chromatids of each chromosome move to opposite poles on the spindle. The separated chromatids are now called chromosomes. TELOPHASE II & CYTOKINESIS II With the formation of four cells, meiosis is over. Each of these prospective germ cells carries half the number of chromosomes of somatic cells. TELOPHASE II & CYTOKINESIS II A nuclear envelope forms around each set of chromosomes. Cytokinesis takes place, producing four daughter cells (gametes, in animals), each with a haploid set of chromosomes. Because of crossing- over, some chromosomes are seen to have recombined segments of the original parental chromosomes. GAMETOGENESIS Gametogenesis represents the collective processes of mitosis, meiosis, and developmental events necessary for the production of male and female gametes in sexual reproduction. Spermatogenesis is the production of sperm cells in the male testis, or sex organ; Oogenesis is the production of eggs in the female ovary. Spermatogenesis n=23 Human germ cell in n=23 sperm testes Still doubled chromosomes n=23 2n = 46 haploid (n) n=23 n=23 Still doubled diploid (2n) chromosomes n=23 meiosis I meiosis II Oogenesis 23 Human germ cell in ovary Polar n=23 Still doubled 23 Bodies 2n = 46 23 n=23 Still doubled diploid (2n) Ovum n=23 meiosis I meiosis II  Sexual Reproduction Fusion of two gametes to produce a single zygote. Introduces greater genetic variation, allows genetic recombination. Zygote has gametes from two different parents (except in cases of self-fertilizing organisms). Rose + Greg = Steven  Sexual reproduction in humans … At fertilization, 23 chromosomes are donated by each parent. (total = 46 or 23 pairs). Gametes (sperm/ova): Contain 22 autosomes and 1 sex chromosome. Are haploid (haploid number “n” = 23 in humans). Fertilization results in diploid zygote. Diploid cell; 2n = 46. (n = 23 in humans) Q: Most cells in the body are produced through what type of cell division? (Remember, only gametes are produced through meiosis)  Genetic Variation in Diploid Organisms Fusion of sperm and egg results in unique offspring… …but not only because the young are a product of two individuals with different genetic makeup. Meiosis also “shuffles” the genes so that the an individual’s gametes are genetically different from one another. How is this shuffling accomplished? Image: Meiosis diagram, Marek Kultys Genetic shuffling of Meiosis I In addition to a new combination of chromosomes resulting from fertilization, there are also events in Meiosis I that shuffle the genes. Crossing over in Prophase I. Independent assortment in Metaphase I. Crossing Over Homologues break at identical locations, then rejoin opposite partners. This creates new combinations of the alleles on each chromosome. Occurs randomly several times on every chromosome. Results in mixing of the genes you inherited from your parents. Independent Assortment Variation from Genetic recombination Independent assortment of chromosomes meiosis introduces genetic variation gametes of offspring do not have same combination of genes as gametes from parents random assortment in humans produces 223 (8,388,608) different combinations in gametes new gametes from Mom from Dad offspring made by offspring THANKS! DO YOU HAVE ANY QUESTIONS? REFERENCES: Bustamante, J. (2023). The Cell. Pdf.