Plant Cell Cycle: Mitosis and Meiosis PDF

Lecture No. 3 Plant Cell Cycle (Mitosis and Meiosis) Prepared by: CHRISTINE JOY S. LUNA  LEARNING OUTCOMES 01 02 Describe the events Compare and of the cell cycle in contrast mitosis plants and meiosis  Growth ❖Dictated by continuous g...

Lecture No. 3 Plant Cell Cycle (Mitosis and Meiosis) Prepared by: CHRISTINE JOY S. LUNA  LEARNING OUTCOMES 01 02 Describe the events Compare and of the cell cycle in contrast mitosis plants and meiosis  Growth ❖Dictated by continuous generation of new cells ❖Achieved through cell expansion and cell division ❖ Cell cycle ❖ “Telomeres”  Chromosome Thread-like structures in a cell’s nucleus that are visible under the microscope only during cell division Consists of proteins and a single large molecule of DNA that contains hundreds of thousands of different genes  Chromosome number The number of chromosomes within a nucleus varies from one species to another, but every somatic cell in an organism of a given species contains a characteristic number of chromosomes. Cabbage: 20 chromosomes per cell (10 pairs per cell) Haplopappus gracilis: 4 chromosomes per cell (2 pairs per cell) Olea europea: 46 chromosomes (23 pairs per cell) Ophioglossum reticulatum: 1262 chromosomes per cell (631 pairs per cell)  Homologous chromosomes Members of a chromosome pair that are similar in size, shape, and genetic constitution. Carry information governing the same genetic traits, although is not necessarily identical. Example: A homologous pair carrying a gene that specifies flower color, but each chromosome may specify different colors of petals.  Diploid vs. Haploid Diploid (2n)- A cell in which each chromosome occurs in pairs Haploid (n)- A cell that has a single set of chromosomes Diploid Haploid Two chromosomes Single Chromosome Represented by 2n Represented by n Somatic cells Gametes Created by Mitosis Created by Meiosis  The Cell Cycle The cell cycle is the successive series of events in the life of a dividing eukaryotic cell. Often represented as a circle and consists of two main phases (interphase and M phase) The period between two successive divisions, represented by a complete revolution of the circle, is The cell cycle the generation time.  Cell Cycle M INTERPHASE (MITOSIS/ MEIOSIS) PHASE Preparatory phase Mitosis Performs Cell growth and DNA Meiosis I duplication Meiosis II  Meristems Localized areas of the plant body where mitosis and cytokinesis take place most of the time. Occur in the shoot and root tips (the apical meristems) and in some plants, in thin cylindrical regions that run the entire lengths of stems and roots except at the tips (the lateral meristems) Apical meristems: allows the production and subsequent elongation of new cells, causing an increase to the length of growing stems and roots. Lateral meristems: produce additional wood and bark tissues that add girth to stems and roots of trees and shrubs.  Interphase The stage between successive cell divisions Interphase: “between phases” The cell synthesizes needed materials and grows Chromosomes undergo duplication during interphase (not readily visible) Interphase SUBPHASES: 1. Gap I Phase (GI Phase) or Pre-synthesis gap 2. Synthesis phase (S Phase) 3. Gap II (GII Phase) or Post-synthesis Interphase: First Gap Phase (G1) First stage in Interphase Pre-synthesis phase Cell growth Duplication of organelles Cell’s nucleus contains single nucleolus and light chromatin materials Does not involve DNA replication GI checkpoint  Interphase: Synthesis Phase (S) Second stage of Interphase Duplication of nucleus Synthesis of DNA and protein “Replicated chromosomes”- chromosomes after S phase Interphase: Secondary Gap Phase (G2) Third step, next to S Phase Post-synthesis phase Allows the cells to grow more More proteins and organelles (e.g.mitochondria, chloroplasts, etc.) are being made Larger nucleus; nucleus contain two nucleoli and darker chromatin materials. Prepares the cell for the actual division (M Phase) Interphase: Gap Zer0 Phase (G0) Gap zero phase or Resting Phase Cells may opt to enter this phase or may directly enter the G1 phase up to cell division Intrinsic and extrinsic factors (resource availability, nutritional deprivation, etc.) A cell is performing its function without actively preparing to divide Quiescent stage Cells enter G0 phase, phase temporarily Senescent stage Cells enter G0 phase permanently Interphase and M Phase Important processes under Interphase 1. DNA Replication ❑ a process of duplicating DNA through semi-conservative replication ❑ Initiation, Transcription, and Translation 2. Transcription ❑ the genetic information in the DNA is transferred to RNA through the catalytic action of RNA polymerase 3. Translation ❑ Translation is the synthesis of a protein from an mRNA template. ❑ Synthesize proteins, which are used for millions of cellular functions. DNA REPLICATION Source: https://www.youtube.com/watch?v=Qqe4thU-os8 Transription and Translation Source: https://www.youtube.com/watch?v=oefAI2x2CQM Transription and Translation Source: https://www.youtube.com/watch?v=bKIpDtJdK8Q M PHASE Mitosis or Meiosis  Mitosis Indicates or signals the completion of interphase Visible changes associated with the division of the nucleus take place Most cellular activities (e.g. Protein synthesis) are suspended during this phase It is divided into four stages  M Phase: Mitosis Facilitates plant growth and repair through mitotic cell division A mechanism that maintains the equal distribution of chromosome content hence, producing two identical cells from a single parent cell. A nuclear division (karyokinesis) that involves condensation and separation of replicated chromosomes. Four stages (PMAP) 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase.  M Phase: Mitosis Mitosis is a carefully controlled process that organizes and separates the chromosomes correctly. After the cells separate the chromosomes and build new nuclei, they divide their cytoplasm by cytokinesis and form two distinct cells. Mitosis  Mitosis: Prophase ❑ Duplicated chromosomes condense and become visible during prophase ❑ Chromatin begins to condense and coil into visible chromosomes. ❑ Chromosomes become shorter and thicker and are individually visible under light microscope  Mitosis: Prophase Chromosomes become shorter and thicker and are individually visible under the light microscope. Each chromosome is a duplicated chromosome, consisting of sister chromatids Centromere- A specialized region of a chromosome. At prophase, sister chromatids are joined in the vicinity of their centromeres. Kinetochore- The portion of the chromosome centromere to which the mitotic spindle fibers attach. Microtubules- function in chromosome distribution during mitosis  Mitosis: Prophase The nuclear envelope breaks apart. Vesicles- small, membrane-enclosed sacs The nucleolus shrinks and disappears Spindle- The structure consisting mainly of microtubules that provides the framework for chromosome movement during cell division  Mitosis: Prophase The spindle microtubules grow and shrink as they move toward the center of the cell in a “search and capture” process. If a microtubule comes near the centromere of a chromosome, the microtubule “captures” it. As the now-tethered chromosome continues moving toward the cell’s midplane, a spindle microtubule from the cell’s other pole attaches to the opposite side of the centromere.  Mitosis: Metaphase Duplicated chromosomes line up on the midplane of the cell Mitotic spindle: completely visible and composed of numerous microtubules that extend from pole to pole. Each chromatid is quite condensed and appears thick and distinct. Individual chromosomes are more distinct in this phase  Mitosis: Anaphase Chromosomes move toward the poles during anaphase This phase begins as the sister chromatids separate Chromatids that are no longer attached to their duplicates are considered independent chromosome Anaphase ends when all the chromosomes have reached the poles  Mitosis: Telophase The final stage of mitosis in which chromosomes arrive at the poles and return to their interphase condition. The chromosomes begin to elongate by uncoiling and then become invisible chromatin threads Two separate nuclei form  Cytokinesis in Plant Cells The division of the cytoplasm that usually accompanies mitosis, generally begins during telophase. Occurs by the formation of a cell plate, a partition between the newly formed nuclei in the equatorial region of the cell. Forms two daughter cells Cytokinesis in Plant Cells  Sexual Reproduction Gametes Reproductive cells (egg and sperm cells) which have half the diploid number of chromosomes. Form a complete, new organism by uniting Zygote A fertilized egg produced upon union of the female gamete (egg) and the male gamete (sperm cell).  Meiosis Reduces the number of chromosomes in reproductive cells by half Meiosis means “to make smaller” As a result of meiosis, each gamete has only one chromosome of each pair, resulting in an egg or sperm cell with a haploid, or n, number of chromosomes.  Meiosis ❖ Each new cell that results from meiosis is a haploid cell; it has n, not 2n, chromosomes ❖Meiosis separates the members of each homologous pair of chromosomes→ No two offspring of the same parents will be exactly alike. ❖Consists of two cell divisions: first and second meiotic divisions (meiosis I and meiosis II) Meiosis I: Prophase I ❖ The chromosomes duplicate during the S Phase of Interphase before the complex movements of meiosis actually begin. ❖ The homologous chromosomes come together to lie side by side lengthwise. ❖ Synapsis- Pairing of homologous chromosomes  Meiosis I: Prophase I ❖ Crossing over The sharing of genetic material between two non-sister chromatids of paired homologous chromosomes Produces new combination of genes  Meiosis I: Prophase I ❖ A spindle forms consisting of microtubules. ❖ The nuclear envelope and nucleolus disappear ❖ In cells with large chromosomes, the association of the four chromatids of each Meiosis I: Metaphase I ❖ Homologous chromosomes line up in pairs along the midplane. ❖ Both kinetochores of one duplicated chromosome are attached by spindle microtubules to the same pole. ❖ Both kinetochores of the duplicated homologous chromosome are attached to the opposite pole  Meiosis I: Metaphase I Spindle microtubules Equatorial plane Metaphase in Mitosis Centromere Chromatid/s Key stages in Plant Meiosis Meiosis I: Anaphase I ❖ The paired homologous chromosomes separate, with one chromosome moving toward one pole and its homologue moving toward the other pole. ❖ Each pole receives a random combination of maternal and paternal chromosomes, but only one member of each homologous pair is present at each pole  Meiosis I: Anaphase I 1. At the onset of anaphase I, each bivalent separate Cell pole Spindle Fibers Key stages in Plant Meiosis Meiosis I: Telophase I ❖ There would be two duplicated chromosomes, one of each homologous pair, at each pole. ❖ The nuclei often reorganize, the chromatids generally elongate, and cytokinesis may take place. Meiosis I: Telophase I Two haploid cells are formed at the end of Meiosis I  Meiosis II: Prophase II ❖ Sister chromatids separate ❖ There is no pairing of homologous chromosomes and no crossing over occurs ❖ Main features: Chromosomes become shorter and thicker, and their two-stranded nature once more becomes apparent  Meiosis II: Metaphase II ❖ The chromosomes, each consisting of two sister chromatids, line up on the midplanes of their cells ❖ There are two chromatids of a single chromosome ❖ Main features: 1. The centromeres of the chromosomes become aligned along the equator. 2. New spindles become conspicuous and complete Meiosis II: Anaphase II ❖ The paired chromosomes separate, with one chromosome moving toward one pole and its homologue moving toward the other pole. ❖ Only one member of each homologous pair is present at each pole. ❖ Main features: The centromeres and chromatids of each chromosome separate and migrate to opposite poles. Meiosis II: Telophase II ❖ There is one member of each homologous chromosome pair at each pole. Each chromosome is in an unduplicated state. ❖ Nuclear enveloped then re-form around each set of chromosomes. ❖ The chromosomes gradually elongate into threadlike chromatin ❖ Cytokinesis occurs ❖ Main features: 1. The coils of the chromatids (now called chromosomes again) relax so that the chromosomes become longer and thinner 2. New nuclear envelopes and nucleoli reappear for each group of chromosomes.  Meiosis I and II ❖ Result in four haploid daughter cells, each containing one of each kind of chromosome. ❖ Each resulting haploid cell has a different combination of genes. ❖ Two sources of genetic variation: 1. DNA segments are exchanged between maternal and paternal homologues during crossing over 2. During Meiosis, the maternal and paternal chromosomes of homologous pairs separate independently so that each member of a pair is randomly distributed to one of the poles at anaphase. A Comparison of Mitosis and Meiosis Importance of Plant Cell Cycle: Mitosis and Meiosis Source: https://www.youtube.com/watch?v=WNkUpdZmM0I Importance of Plant Cell Cycle: Mitosis and Meiosis Source: https://www.youtube.com/watch?v=iRKu2MN4T04  LEARNING OUTCOMES 01 02 Describe the events Compare and of the cell cycle in contrast mitosis plants and meiosis  Any questions? Email: [email protected] Contact number: 09478446564