Lec5-Cell III-Student Notes.pdf

Lec#5: Cellular Level III- Cell Division Menu LO1-5 Section A: Somatic Cell Division LO6-8 Section B: Reproductive cell division ©Beatriz Castro ...

Lec#5: Cellular Level III- Cell Division Menu LO1-5 Section A: Somatic Cell Division LO6-8 Section B: Reproductive cell division ©Beatriz Castro  LO1: Describe the events that take The period of a cell’s life when place in each stage of the cell cycle it carries out its normal metabolic activities and grows The Cell Cycle is a series of events involving cell growth and cell division. 3 Stages: G1, S, and G2 Two main phases : interphase & mitotic (M) Cells spend most of their lives here, specifically in the S phase. Cell division occurs during the M phase. It consists of two distinct phases: Mitosis = nuclear division Cytokinesis = division of the cytoplasm  INTERPHASE S (Synthesis of DNA)- Takes up the responsibility of duplication of DNA and Centrosome G1 (First Gap) Organelles duplicate G2 (Second Gap)- Cell grows more is size. More protein synthesis, builds enzymes. Makes more duplicates of some Resting or inactive stage organelles. Prepares the cell for (quiescent state) where a Mitosis. cell exits the cell cycle Infinity Learn NEET https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_(Boundless)/10%3A_Cell_Reproduction/10.02%3A_The_Cell_Cycle/10.2A%3A_Interphase#:~:text=There%20are%20three%20stages%20of,in%20the%20G1%20phase.  MITOSIS Prophase → Metaphase → Anaphase → Telophase Throughout interphase, nuclear DNA remains in a semi-condensed chromatin configuration Nuclear envelope and nucleoli are intact and visible. IPMAT 4 1 Late prophase (prometaphase) Interphase is part of the 2 cell cycle, but mitosis 3 begins with prophase Mitosis ensure that each new cell has the exact same number of chromosomes as the original  1 Late Prophase (Prometaphase) microtubule-based structure that controls the proper Allowing the segregation of chromosomes during mitosis spindle to interact with chromosomes Mitotic spindle begins to form from centrosomes. Microtubule arrays called asters (“stars”) extend from the centrosome matrix. As the microtubules lengthen, they propel the centrosomes toward opposite ends (poles) of the cell Some of the growing spindle (duplicated) (chromatin coils microtubules attach to kinetochores at and condenses) each centromere--- they start pulling on each chromosome from both poles nucleoli disappear drawing them to the center (equator) of the cell https://www.medschoolcoach.com/mitosis-mcat-biology/ Image Source: Khan Academy.  2 chromosomes line up on the equator (along the metaphase plate) Centrioles Chromosome= 2 sister chromatids joined at centromere (kinetochore microtubules) central region - Metaphase plate where sister The imaginary plane midway between the poles chromatids are attached protein complex on the centromere that spindle fibers because mitosis occurs after DNA replication, each attach to chromosome consists of two identical sister chromatids https://www.medschoolcoach.com/mitosis-mcat-biology/  It begins as soon as chromosomal 4 movement stops. This final phase is like prophase in reverse: chromosomes uncoil and resume their threadlike chromatin form, a new nuclear envelope forms, nucleoli reappear, and the spindle breaks down and disappears. The shortest phase 3 (3.3) Somemicrotubules lengthen and push the two poles of the cell apart. (3.2) The kinetochore microtubules gradually pull each chromosome toward the pole it faces Sister chromatids The moving chromosomes look V shaped (3.1) the centromeres of the chromosomes split simultaneously. Each chromatid now becomes a chromosome in its own right.  LO2: Distinguish between mitosis and cytokinesis. Telophase Mitosis focuses solely on the division of the cell's nucleus. Cytokinesis: This phase deals with the physical division of the cell's cytoplasm and organelles. It begins late in mitosis and ensures the two daughter nuclei end up in separate cells. A contractile ring of actin microfilaments that pinches the cell apart. © Pearson, Inc. 2018  LO3: Analyze the interrelationships among chromatin, chromosomes, and chromatids. As a cell prepares for division, chromatin undergoes further condensation, chromatin fibers fold and loop, ultimately giving rise to visible chromosomes. Chromatids are the two identical halves (“sister chromatids”) of a duplicated chromosome held together at the centromere. Each chromatid consists of a single DNA molecule tightly coiled with proteins - they contain identical genetic information Chromatin: a complex of DNA tightly packaged with histone proteins.  (after replication) (1 chromatid) (2 chromatids) an electron micrograph of human chromosome 2 The centromere often divides the chromosome into two parts that are referred to as the short arm (p arm for petite) and the long arm (q arm) 2 Forms of chromatin: Heterochromatin vs Euchromatin The key difference lies in how tightly packed the DNA is and how active the genes are in that region. Heterochromatin Euchromatin ~ 90% Tightly packed DNA Loosely packed DNA Appears darkly stained under a lightly stained microscope Gene-poor Gene-rich Inactive or rarely transcribed Actively transcribed (genes are being used to make proteins) Electron-microscopic picture of an interphase nucleus 2 Main types: Constitutive: permanent and always tightly packed and inactive. It contains repetitive DNA. It helps maintain chromosome structure. It's found in regions like centromeres and telomeres. Facultative: Can become active or inactive depending on the cell's needs. Carlberg, C., Molnár, F. (2016). The Impact of Chromatin. In: Mechanisms of Gene Regulation. Springer, Dordrecht. https://doi.org/10.1007/978-94-017-7741-4_2 https://doi.org/10.1016/j.ijbiomac.2017.03.165 A checkpoint is a stage LO4: Indicate the three main cell cycle checkpoints & regulators in the cell cycle at which the cell examines internal and external cues and “decides” How’s our DNA? whether or not to move Did all the chromosomes get forward with division replicated correctly? Is the DNA damage? If errors are detected, the cell will delay mitosis until repairs are made. Are we ready to divide? Is the cell big enough? Are there enough energy and other reserves? Is the DNA damaged? (DNA integrity) How’s our chromosomal alignment? Did all the chromosomes line up in the center of the cell, ready to be pulled apart? https://openoregon.pressbooks.pub/mhccbiology112/chapter/10-3-control-of-the-cell-cycle/ LO4: Positive regulators of the cell cycle: Negative regulatory molecules: They activate other proteins that help the cell cycle (called tumor suppressors) to move forward through the various checkpoints. Rb, p53, and p21 act primarily at the G1 checkpoint Two groups of proteins: p21 is produced in response to p53 and cyclin-dependent If it detects DNA stops the cell cycle by kinases (CDKs) damage which can’t be inhibiting CDK/cyclins. repaired, it tells the cell to commit suicide. Cyclins are active only when they are tightly bound to CDKs. Inhibits E2F Transcription Factors, which are critical Retinoblastoma regulators of genes involved in protein DNA replication These control molecules determine whether or not the cell is prepared to move into the following stage. https://openoregon.pressbooks.pub/mhccbiology112/chapter/10-3-control-of-the-cell-cycle/ Photo credit: Lisa Bartee, CCBY 4.0  LO5: Give examples of cell types in the body that divide by mitosis and examples of circumstances in the body that require mitotic cell division. Mitosis is the primary mode of cell division Growth & Development for most cells in the body. It allows for the multiplication of cells to Growth & Development build tissues, organs, and entire systems. Maintenance of Tissues Tissue Repair after injury e.g. Skin cells undergo regular mitotic division to e.g. Skin cells rapidly replace dead or damaged Maintenance Tissue Repair divide to heal wounds, cells on the surface, of Tissues after injury and bone cells Circumstances maintaining the skin barrier. Requiring undergo mitosis to Mitotic Cell mend fractures. Division in the Body: Cell Proliferation in Immune Response Replacement of Short-lived Cells Cell Replacement Mitosis in precursor cells within immune cells like lymphocytes undergo Proliferation of Short-lived the bone marrow continuously rapid mitotic division to generate a large in Immune Cells produces new red blood cells to number of cells to combat the infection. Response maintain their numbers  LO6: Give examples of cell types in the body that divide by meiosis. The purpose of meiosis is to produce gametes, the sperm and eggs, with half of the genetic complement of the parent cells– “reduction division” Haploid (n) = 1 copy of each diploid(2n) = 2 copies chromosome. In humans, of each chromosome. that is 23 chromosomes. In humans, that is 46 chromosomes. Ordinary body cells have a complete set of chromosomes. If body cells from mom and dad fused to form a baby, the fertilized egg would have twice as many chromosomes as it should. https://www.shalom-education.com/courses/gcse-biology/lessons/genetic-variation-and-mutation/topic/meiosis/  LO7: Describe the events that take place in each stage of meiosis I and meiosis II For simplicity, only two pairs of homologous chromosomes with different lengths are shown. Each homologous chromosome has two chromosomes (blue and red) which distinguish the different parental origins. Curr. Issues Mol. Biol. 2023, 45(10), 7974-7995; https://doi.org/10.3390/cimb45100504  5 Phases: Synaptonemal complex Protein structure that hold paired chromosomes together (2) Zygotene (3) Pachytene (1) Leptotene Homologous chromosomes pair up with Crossing over (exchange of Replicated chromosomes each other, a process called synapsis. condense and become genetic material) occurs. visible as thin threads. The point where a crossover occurs (plural: chiasmata) crossovers= cross-connections that form from breakage and rejoining DNA segments b/w sister chromatids ↑ Genetic diversity in offsprings Ali Zifan - using: information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman. http://cyberbridge.mcb.harvard.edu/mitosis_6.html  5 Phases: (4) Diplotene (5) Diakinesis synaptonemal complex begins to break Chromosomes continue to condense, down; they are still held together at the becoming shorter and thicker. points where crossing over occurred (chiasmata) Ali Zifan - using: information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman.  Same events than in mitosis Homologous chromosomes (containing 2 sister chromatids) move For the next steps let’s focus only on this cell Pairs of homologous chromosomes to the opposite poles of the cell the cell divides via cytokinesis (4 chromatids=tetrads) move to the forming 2 haploid daughter cells equator of the cell (metaphase plate) Ali Zifan - using: information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman. x2 In each of the daughter cells: the nuclear envelope breaks down, and the chromatin condenses into chromosomes again. The basic events are similar in Meiosis II & Mitosis Ali Zifan - using: information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman.  LO8: Compare and contrast the general features of meiosis I and meiosis II. SIMILARITIES: Consists of 4 stages (prophase, metaphase, anaphase, and telophase). Involves division of nucleus and cytoplasm. Stage Meiosis I Meiosis II Prophase Synapsis (pairing) No synapsis. Crossing over (genetic exchange) No crossing over. Metaphase Paired homologous chromosomes line Sister chromatids line up at equator up at equator Anaphase Paired homologous chromosomes Sister chromatids separate and move to separate and move to opposite poles opposite poles At the end 2 haploid cells are formed 4 haploid cells are formed https://courses.lumenlearning.com/suny-biology1/chapter/the-process-of-meiosis/ Overview