Biology Module 1 Lesson 2: Cell Cycle and Cell Division (2022-2023) PDF

BIOLOGY 11-2 ROGER (2022-2023) – FIRST SEMESTER MODULE 1 Lesson 2: Cell Cycle and Cell Division 09/05/22...

BIOLOGY 11-2 ROGER (2022-2023) – FIRST SEMESTER MODULE 1 Lesson 2: Cell Cycle and Cell Division 09/05/22 OUTLINE Figure 2. Cyclin and CDK Activity I. Cell Cycle III. Mitosis vs. Meiosis A. Cell Cycle Control IV. More on Chromosomes System V. Human-Focused Meiosis B. Interphase VI. Review Questions C. Cancer Cells VII. References II. Cell Division A. Mitotic Phase B. Meiosis I. CELL CYCLE - Ordered sequence of events in the life of a eukaryotic cell Phases of Cell Cycle ○ Gap 1: Cell growth ○ Synthesis: Most complicated phase, DNA replication. ○ Gap 2: Cellular organelles replication. External Growth Factor – PDA ○ G0: Resting or Inactive - These are released by cells and stimulate other cells to ○ Mitosis: Shortest phase, cell division. divide. A. Cell Cycle Control System Platelet-derived growth factor: made by platelets every time - The cycle seems to be driven by chemical signals present in it's required (may be due to an injury). the cytoplasm. Its sequential events are directed by a distinct Density-dependent inhibition: a phenomenon wherein control system similar to a clock. crowded cells will stop dividing when they come in contact with each other because they need space. - Internal control has checkpoints that signal the cell if it can Anchorage dependence: in animal cells, they must be proceed to the next stage. attached to a substratum or extracellular matrix to divide. Figure 1. Cell Cycle Clock Control System B. Interphase - About 90% of the cell cycle. During interphase, cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. Gap 1 (G1) ○ Where cells grow ○ Checkpoint 1: go signal means the cell will undergo the whole cell cycle while a stop signal will put the cell into the G0 phase. Also checks that the cells are growing properly. Most important because the whole cell cycle is dependent on it (- Ms. Deque). Synthesis (S) ○ Where DNA is synthesized and allows the daughter cells to have an identical genetic make-up. ○ Accurate duplication of the genome is critical to successful cell division, the processes that occur during S-phase are tightly regulated and widely conserved. ○ Sister chromatids: identical copies of a chromosome that are created during the synthesis phase. Cyclin Expression Cycle Gap 2 (G2) Cyclins and Cyclin-dependent Kinases are two types of ○ Intensive cellular synthesis. Mitochondria, regulatory proteins. CDK rises and falls with changes in the chloroplasts, and other organelles divide. Energy concentration of its cyclin partner. stores increase. MPF (maturation/mitotic-promoting factor): a cyclin-CDK ○ Checkpoint 2: All the materials are present and the combination that triggers a cell's passage past the G2 DNAs are properly duplicated and are healthy, this checkpoint into the mitotic phase. will then give a go signal for the cells to divide. Cyclins: regulatory proteins whose concentration fluctuates Ensures that the two daughter cells will have the cyclically. same amount of organelles. Cyclin-dependent Kinases: a protein kinase that is only active when attached to a particular cyclin. 1  Gap 0 (Gθ) Anaphase ○ When cells aren't partaking in the cell cycle and only ○ Sister chromatids separate and are moving toward undergo the cycle when needed. For example, liver the poles of the cell. Centrosomes push out, and cells and neurons only regenerate when needed. microtubules shorten. Quickest stage. C. Cancer Cells Telophase They do not follow the body's control mechanism and may ○ Nuclear envelope reforms, chromosomes have their own growth factors. When not eliminated by the decondense, mitotic spindle breaks; cytokinesis immune system they form tumors or masses. simultaneous. ○ Simplified: the daughter cells are forming and Types of Tumors obviously the cytokinesis will follow to have a fully ○ If abnormal cells only stay in one place, it’s benign. divided cell. ○ Malignant tumors may invade other parts or surrounding tissues (metastasis). Cytokinesis ○ Division of the cytoplasm to form two separate Cancer cells do not need growth factors to grow and divide. daughter cells immediately following mitosis ○ They may make their own growth factors. ○ Cleavage: Process of cytokinesis in animal cells ○ They may convey a growth factor’s signal without characterized by pinching of the plasma membrane. the presence of a growth factor. Also, the succession of rapid cell divisions without ○ They may have an abnormal cell cycle control growth during early embryonic development system. converts the zygote into a ball of cells. Also known as the Cleavage furrow: The indentation at the Cells that acquire the ability to divide indefinitely are center of a dividing cell, which ingresses into a undergoing transformation. bridge that connects the two daughter cells. ○ Metastasis: the spread of cancer cells to other body Compressive or contractile stress. parts, where they may form additional tumors ○ Cell Plate: Double membrane across the midline of a dividing plant cell, between which the new cell wall Figure 3: The growth and metastasis of a malignant breast tumor form during cytokinesis Figure 4: Cell Furrow and Cell Plate II. CELL DIVISION Binary Fission ○ Prokaryotes reproduction; each dividing daughter cell receives a copy of the single parental chromosome. A. Mitotic Phase - A phase in the cell cycle that includes both mitosis and cytokinesis. It occurs in eukaryotic cells only. - Mitosis is important because it produces body cells for growth and to repair damages. Prophase ○ Chromatin condenses, centrosomes separate, and formation of the mitotic spindle. Nucleolus disappears. Prometaphase ○ Nuclear envelope breaks, and fully stretched microtubules. Metaphase ○ Chromosomes are lined up and each sister chromatid is attached to a spindle fiber. ○ Checkpoint 3: To make sure that all chromosomes are attached to the microtubules during the mitotic spindle so that the daughter cells will have an equal amount of chromosomes. If the chromosomes are not properly attached stop signals are received. 2 Figure 5: Mitosis Visualization Zygotes: The fertilized egg; it'll be diploid because it gets one chromosome from each parent. The zygote produces somatic cells by mitosis and develops into an adult. Gametes: The only cell from the human body that's not produced by mitosis. It's developed from germ cells from the gonads. Only has 23 chromosomes! Stages of Meiosis ○ Chromosome duplication ○ The resulting sister chromatids are closely associated along their lengths called sister chromatid cohesion. ○ The chromatids are then sorted into four haploid daughter cells. Figure 6: Meiosis Simplified Important Key Terms Homologous chromosomes: two chromosomes that are the Chromatin (Thread-like) same size and contain the same types of genes in the same ○ DNA and proteins that make up chromosomes. location; pair of chromosomes. ○ Tetrad: two homologous chromosomes that are Centrosome attached together because it will consist of four ○ Microtubule organizing center. chromatids. Also called synapsis. Apoptosis Figure 7: Sister and Non-sister Chromatids ○ Programmed cell death Kinetochores ○ Proteins on the side of centrosomes that help microtubules pull sister chromatids apart during cell division, and acts like a glue sticking the sister chromatids to the microtubules (- ms deque). B. Meiosis - It is the process of reduction division in which the number of chromosomes per cell is cut in half throughout the separation of homologous chromosomes in a diploid cell. For the production of GAMETES. - Meiosis is preceded by the replication of chromosomes and takes place in two consecutive cell divisions called meiosis I and meiosis II. - Generally, germ cells which are specialized diploid cells, undergo meiosis to produce sperm cells and egg cells. Fertilization: Union of gametes. The beginning of life is when a haploid sperm cell fuses with a haploid egg cell. Fertilization and meiosis alternate in sexual life cycles to maintain chromosome numbers. 3  Interphase Telophase I - Before meiosis occurs the cell undergoes growth, synthesis, ○ Chromosomes arrive at poles; nuclear membranes and functioning. During the DNA duplication, the reform as spindle breaks down; cell furrow forms; chromosomes are replicated from 46 chromosomes (46 cytokinesis occurs. chromatids) to 46 chromosomes (92 chromatids). ○ Each half of the cell has a haploid set of - Simplified: initially, the chromosomes have unpaired sister chromosomes two unduplicated sister chromatids chromatids so it’s like one strand only. When duplicated, it because they’re no longer identical. became two strands, so from 46 chromatids to 92 chromatids. Unique Events in Meiosis I Meiosis I ○ Synapsis and crossing over in prophase I: - Simplified: Separates two homologous chromosomes into Homologous chromosomes physically connect and sister chromatids. exchange genetic information. ○ Homologous pairs at the metaphase plate. Prophase I (Busy Time) ○ Separation of homologs during anaphase I. ○ Fragmentation of nuclear envelope, condensation of chromosomes, and formation of the spindle. Meiosis II ○ Synapsis: the tight pairing of the homologous - Simplified: Separates sister chromatids; Similar to mitosis! chromosomes. ○ In order to hold the homologs together, the Prophase II synaptonemal complex forms which facilitates the ○ Fragmentation of nuclear envelope, condensation of exchange of corresponding random pieces of DNA chromosomes, and formation of the spindle. between non-sister chromatids, yielding new Whatever happens in the mitosis prophase also combinations of alleles via homologous happens here. recombination. Chromatids intertwine, breaking ○ Main difference is that the sister chromatids aren’t apart and exchanging pieces with one other in a identical. process called crossing-over. ○ Chiasmata: x-shaped regions that are sites for Metaphase II crossovers and mark the areas where crossover. ○ The chromosomes line up at the metaphase plate. ○ The unduplicated sister chromatids attach Figure 8: Enhanced Prophase I themselves to the microtubules. Anaphase II ○ Sister chromatids separate. Due to the degradation of the proteins that attach the chromatids together, the microtubules easily pull apart the chromatids. Telophase II ○ Nuclear envelope starts to form, the microtubules disappear, and the single-stranded chromosomes start to decondense into chromatin. ○ Genetically, the four daughter cells are not identical because the final unduplicated sister chromatids are different due to the crossover. ○ Cytokinesis occurs. Meiosis Final Product From a diploid germ cell, the final product becomes a haploid gamete with one chromatid. Figure 9: Meiosis I Simplified Metaphase I ○ The homologous chromosomes line up at the metaphase plate with one chromosome facing each pole, and are attached to the spindle to be pulled apart. ○ Ultimately determines which chromosomes end up in gametes. Anaphase I ○ The homologous chromosomes start to separate by the movement of spindle fibers towards the poles of the cell. ○ The synaptonemal complexes that attach the homologous chromosomes together are broken down. 4 Figure 10: Meiosis II Simplified IV. CHROMOSOMES Sister chromatids: Chromatids are generally duplicated chromosomes that have a centromere. Cohesins: proteins that bond sister chromatids together. Diploid: Two copies of each chromosome, one from each parent. Somatic cells are always diploid. Important Key Terms Heredity: The transmission of traits from one generation to the next. Variation: Demonstrated by the differences in appearance that offspring show from parents and siblings. Genes: Units of heredity that are made up of segments of DNA. Passed down via reproductive cells called gametes. Humans have 46 chromosomes in the nuclei of their somatic cells, all cells of the body except gametes and their V. HUMAN-FOCUSED MEIOSIS (EXTRA) precursors. Oogenesis Genetic Recombination: The result of the exchange of Production of egg cells that occurs in ovaries. Only one out of alleles between homologous chromosomes which produces a the four daughter cells will mature. new combination of alleles. Polar bodies: cells produced in females that do NOT participate in reproduction. They receive less cytoplasm due Locus: A gene's specific position along a chromosome. to unequal cytokinesis; cell furrow does not form along the equator; instead, it forms off-center. They die and get III. MITOSIS vs. MEIOSIS reabsorbed. Oocyte: The starting cell of meiosis in females, it’s a specialized diploid cell with 46 chromosomes. Ootid: The only cell that matures into an ovum, formed at the end of oogenesis. Has larger cytoplasm to ensure that it’ll mature properly. Figure 11: Oogenesis Visualization 5  Spermatogenesis A. QA MOCK QUIZ Formation of sperms that occurs in testes. https://quizizz.com/join/quiz/63307b1efbb5f3001d3dc3e7/start Spermatocyte: The starting cell of meiosis in males, it’s a ?studentShare=true specialized diploid cell with 46 chromosomes. Figure 12: Spermatogenesis Visualization VI. REVIEW QUESTIONS 1. An enzyme that activates or inactivates other proteins by phosphorylating them. Give the go-ahead signals at the G1 and G2 checkpoints. - Protein Kinase 2. A Maturation-promoting factor (M-phase promoting factor); specific cyclin-Cdk complex which allows cells to pass G2 and go to the M phase. The active form consists of cyclin and a protein kinase - MPF 3. The requirement that to divide, a cell must be attached to the substratum. - Anchorage-dependence 4. The complete set of genes or genetic material present in a cell or organism. - Genome 5. A protein that must be present in the extracellular environment for growth and normal development of certain types of cells; a local regulator that acts on nearby cells to stimulate cell proliferation and differentiation - Growth factor 6. an ordered sequence of events in the life of a eukaryotic cell, from its origin in the division of a parent cell until its own division into two. - Cell Cycle 7. A two-stage type of cell division in sexually reproducing organisms that results in cells with half the chromosome number of the original cell. - Meiosis 8. What proteins hold together the sister chromatids? - Cohesins 9. What does "crossing over" ensure? - Variation among specie 6