Mitosis Lesson Notes

Mitosis ✓ Cell replication in which one cell (the parent cell) produces to identical (daughter cells). ✓ The daughter cells (somatic cell, i.e. body cells) that are produced through mitosis allow growth, repair, asexual reproduction and regeneration in multicellular organisms. Key cell structures that are used during cell replication Structure Centriole Centrosome Spindles RNA Definition A complex of microtubules, protein and a matrix that form part of the centrosome. Two centrioles combined at right angles and surrounded by a matrix that helps produce and organise spindle fibres. Lengths of microtubules that lengthen or contract to move the chromatids to different poles of new cells. Ribonucleic acid; a macromolecule related to DNA that plays an important part in protein manufacture in the cell. Cell replication in eukaryotes (multicellular organisms) Steps to mitosis Interphase ✓ The DNA in the cell is copied in preparation for cell division, this results in two identical full sets of chromosomes. ✓ Outside of the nucleus are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division. ✓ During interphase, microtubules extend from these centrosomes Prophase ✓ The chromosomes condense into X-shaped structures that can be easily seen under a microscope. ✓ Each chromosome is composed of two sister chromatids, containing identical genetic information. ✓ The chromosomes pair up so that both copies of chromosome 1 are together, both copies of chromosome 2 are together, and so on. ✓ At the end of prophase, the membrane (selective barrier) around the nucleus in the cell dissolves away releasing the chromosomes. The membrane around the nucleus disappears so that the chromosomes have a flexibility in movement, so that during the later steps, the chromosomes can line up at the equator and the sister chromatids split and are pulled to opposite ends. ✓ The mitotic spindle, consisting of the microtubules and other proteins, extends across the cell between the centrioles as they move to opposite poles of the cell. Metaphase ✓ The chromosomes line up neatly end-to-end along the centre (equator) of the cell. ✓ The centrioles are now at opposite poles of the cell with the mitotic spindle fibres extending from them. ✓ The mitotic spindle fibres attach to each of the sister chromatids. Anaphase ✓ The sister chromatids split (i.e. the chromosome splits into two sister chromatids) are then pulled apart by the mitotic spindle which pulls one chromatid to one pole and the other chromatid to the opposite pole. Telophase ✓ At each pole of the cell a full set of chromosomes gather together. ✓ A membrane forms around each set of chromosomes to create two identical new nuclei (one nucleus in each. Nuclei is the plural for nucleus. ✓ The single cell then pinches (divides/separates) in the middle to form two separate daughter cells each containing a full set of chromosomes within a nucleus. This process is known as cytokinesis. Cytokinesis ✓ Division is complete and we have two identical daughter cells ✓ Refers to the cytoplasmic division at the end of mitosis and meiosis. ✓ Cytokinesis begins in anaphase in animal cells and prophase in plant cells, and terminates in telophase in both, to form the two daughter cells produced by mitosis. Cell Replication in Prokaryotes 1. Replication of the circular chromosome and its DNA starts from one point of origin and proceeds in opposite directions it proceeds around the circle unit two new loops form; each loop contains one of the original strands of DNA and one new strands. 2. The two circular chromosomes attach to different parts of cell membrane. 3. The cell elongates (lengthens), separating the two circular chromosomes. 4. A cleavage furrow and septum begin to form across the divide between the two chromosomes. 5. The cell divides into two, resulting into two identical cells formed in a process called binary fission. Prokaryotic organisms are unicellular organisms, meaning they are single celled. They undergo asexual reproduction. For example, fungi, virus, bacteria. Eukaryotic organisms are multicellular organisms, meaning they have more than one cells. They undergo sexual reproduction. Meiosis Production of gametes (egg and sperm). Interphase Prophase I In Prophase I homologous chromosomes pair and exchange DNA and recombinant chromosomes are formed. Metaphase I The homologous pairs of chromosomes are arranged in a double row along the metaphase plate. These chromosomes are randomly arranged along the metaphase plate. Anaphase I In this phase separation of pair of homologous chromosomes occur and they migrate to the opposite ends of the cell. Telophase I In the final stage of meiosis, I, chromosomes become diffuse and reformation of nuclear membrane occurs. Cytokinesis Here, cells are finally divided to form two new cells, followed by Meiosis II. The Haploid cells (newly formed) consist of one copy of each chromosome. Prophase II The chromosomes become visible, the nuclear envelope disappears, and the centrioles form the spindle fibres. Metaphase II The chromosomes line up along the middle line on the spindle fibres Anaphase II The chromosomes get split into its two chromatids. Chromatids are the two strands of DNA (deoxyribo-nucleic acid) that make up the chromosome. They are joined by a mid-way connection called a centromere. (Cytokinesis takes place. The cell divides.) Telophase II The cells are completely divided. The nucleic envelope reforms and four new cells with different DNA are create. The product of mitosis is diploid. The product of meiosis is haploid. Similarities Both involve cell replication Needed for continuity of life Both have phase I Differences Meiosis has two phases, but mitosis has one phase The product of mitosis is diploid. The product of meiosis is haploid. Mitosis production of somatic cells (body cells) Meiosis production of gametes (sex cells)