Lecture 13: Cell Division And Cell Cycle (Part 1) PDF

Lecture 13 Cell Division and Cell Cycle (Part 1) Objectives: Cell theory Prokaryotic cell division Eukaryotic cell division: mitosis Textbook reference sections/pages: Morris text – Chapter 11 (pp. 226-230) Section 11.4 Mitotic Cell Division (pp. 226- 230) BIOL1010 a...

Lecture 13 Cell Division and Cell Cycle (Part 1) Objectives: Cell theory Prokaryotic cell division Eukaryotic cell division: mitosis Textbook reference sections/pages: Morris text – Chapter 11 (pp. 226-230) Section 11.4 Mitotic Cell Division (pp. 226- 230) BIOL1010 and  Cell Theory Cell Theory: one of the fundamental principles of modern biology Four major points to this theory: 1. All organisms are composed of cells or cell products. 2. All the cells in an organism have the “same” DNA and number of chromosomes (unless they are sex cells) 3. The chemical reactions characteristic of living systems occur within cells. 4. All cells arise from pre-existing cells. Slide 2 BIOL1010 and  Overview of Cell Division Cells reproduce via cell division Key Roles of Cell Division: – Reproduction Unicellular organisms – Growth/Development Multicellular organisms – Cell repair/regeneration Multicellular organisms Slide 3 BIOL1010 and  Overview of Cell Division Cell division is the process by which a single cell becomes two daughter cells Cell division involves division of the nucleus and cytoplasm – Karyokinesis – division of nucleus – Cytokinesis – division of cytoplasm via formation of cleavage furrow Requirements for successful cell division: – Full complement of DNA must be distributed to the two daughter cells from single parent cell – Parent cell must be large enough to divide in two and still contribute cytoplasmic components to each daughter cell Slide 4 BIOL1010 and  Overview of Cell Division Methods of Cell Division: – Binary fission Asexual reproduction New copy may be identical or have mutations Prokaryotes (e.g. Bacteria) and other single-celled organisms (Amoebae, Paramecia etc.) – Mitosis Somatic cells Eukaryotic Cell Division Produces exact copies of parental chromosomes – Meiosis Makes sexual reproduction possible! Produces daughter cells (gametes) with half the number of chromosomes compared to parent cell Not exact copies! Slide 5 BIOL1010 and  Prokaryotic Cell Division Binary Fission Most bacteria - one circular chromosome, highly folded and coiled Replication of DNA: Cell increases in size Two important regions on DNA Origin of replication Terminus of replication DNA segregation: Two origins (attached to plasma membrane) move apart Cytokinesis: Pinching in of plasma membrane; synthesis of new cell wall materials Slide 6 BIOL1010 and  Eukaryotic Cell Division Mitosis – Result - two identical daughter cells with same number of chromosomes as parent – Still involves general steps seen in binary fission but more complex than in prokaryotes! – Why? Prokaryotes: Eukaryotes: Slide 7 BIOL1010 and  Eukaryotic Cell Division – Cell Cycle Cell division proceeds through a number of steps that make up the cell cycle Two distinct stages: – M phase: the time during which the parent cell divides into two daughter cells – Interphase: the time between two successive M phases G1 S G2 Slide 8 BIOL1010 and  Eukaryotic Cell Division – Cell Cycle What about G0 phase? – Not all body cells actively participate in cell cycle – Many cells pause between M and S phase – G0 cells remain active in other ways E.g. liver cells metabolize and detoxify E.g. nerve cells enter G0 permanently Slide 9 BIOL1010 and Mitotic Cell Division (Eukaryotes) Chromosome Structure In eukaryotic cells, DNA is organized with histones and other proteins into chromatin Chromatin can be looped and packaged to form chromosomes Slide 10 BIOL1010 and Mitotic Cell Division (Eukaryotes) Karyotype: The portrait formed by the number and shapes of chromosomes representative of a species is called its karyotype In humans: Somatic cells – 46 chromosomes Gametes – 23 chromosomes Human karyotype: Slide 11 BIOL1010 and 22 pairs of homologous Mitotic Cell Division (Eukaryotes) Homologous Chromosomes Two of the same type of chromosome = homologous chromosomes Each carries same set of genes One homologue is paternal chromosome The other homologue is maternal chromosome Number of complete chromosome sets =12 Slide BIOL1010 and Mitotic Cell Division (Eukaryotes) Homologous Chromosomes and Sister Chromatids: – For cell division to proceed normally, every chromosome in parent cell must be duplicated so each daughter cell gets a full set of chromosomes – During which phase of the cell cycle does duplication occur? – After duplication of DNA, each chromosome is made up of two sister chromatids Slide 13 BIOL1010 and Mitotic Cell Division (Eukaryotes) Homologous Chromosomes and Sister Chromatids: – Sister chromatids are held together at centromere Note: to count the number of chromosomes, count the centromeres Slide 14 BIOL1010 and Test Your Understanding…. A B Which is Haploid/Diploid? C D Haploid/ Haploid/ Diploid? Diploid? Slide 15 BIOL1010 and Test Your Understanding… Have these chromosomes replicated? Cell cycle stage? Is this a somatic cell or a gamete? Haploid or diploid? How many chromosomes in total? How many chromatids? How many homologous pairs? Slide 16 BIOL1010 and  Exploring Mitosis 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase Mitosis 5. Telophase video Remember: In interphase, you cannot distinguish specific chromosomes because they are all long and thin. Slide 17 BIOL1010 and  Exploring Mitosis Prophase What are mitotic spindles made up of? What is the significance of the centrosome? Sister chromatids joined together by cohesins Prometaphase Nuclear membrane break-down Spindles attach to chromo-somes (kinetochores) Microtubules polymerize and depolymerize Slide 18 BIOL1010 and  Exploring Mitosis What do Kinetochores look like? Protein complexes Each kinetochore associated with one of sister chromatids Attachment site for single spindle microtubule Slide 19 BIOL1010 and  Exploring Mitosis Metaphase Alignment of chromosomes at metaphase plate Anaphase Sister chromatids separate – Cohesin proteins cleaved Non- Equal segregation of chromosomes! kinetochore BIOL1010 and microtubules Slide 20  Exploring Mitosis Telophase Cytokinesis (Animal) Cytokinesis (Plant) Actin, contractile ring, cleavage furrow Phragmoplast, vesicles, cell plate Result: two diploid cells; genetically identical to parent cell Slide 21 BIOL1010 and  Next Time… Control of cell cycle Meiosis 22 BIOL1010 and