Cell Cycle & Cell Division PDF

CELL CYCLE & CELL DIVISION PREPARED BY: AIMIE A. CASTRO, MST Science Instructor  LEARNING OBJECTIVES At the end of the chapter, the students should be able to: discuss the stages distinguish differentiate sexual of mitosis and...

CELL CYCLE & CELL DIVISION PREPARED BY: AIMIE A. CASTRO, MST Science Instructor  LEARNING OBJECTIVES At the end of the chapter, the students should be able to: discuss the stages distinguish differentiate sexual of mitosis and spermatogenesis and asexual meiosis; from oogenesis; and reproduction. CELL CYCLE During cell cycle, the cell grows , Is the series of prepares for events that cells go division, and divides through as they to form two grow and divide. daughter cells, each of which begins the cycle again.  Cell Division Types of cell: A. Somatic cells ❖ refers to all body cells except sex cells. ❖ contain diploid (2n) number of chromosomes. ❖ contains 46 chromosomes or 23 pairs of chromosomes as the original number of chromosomes. (2 sets of chromosome) ❖ undergo mitosis  Cell Division Types of cell: B. Sex cells/ Reproductive cells/ Gametes/Germ cells ❖ ovum/ova = produced from female reproductive organ. ❖ spermatozoa= produced from male reproductive organ. ❖ contain 23 chromosomes; 1 set ❖ haploid (n)= contain half of the original number of chromosomes.  XXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXX 22ND pair is called the autosomes. 23RD pair is called the sex chromosomes. Homologous chromosomes Same length Same position of centromere Same genes but not necessarily the same allele.  TYPES OF CHROMOSOMES Telocentric- centromere is at the end. Acrocentric- centromere is near the end. Submetacentric- centromere is between center and the end. Metacentric- centromere is at the center. Parts of the Chromosome THE CELL CYCLE  INTERPHASE -the preparatory stage for mitosis not the resting stage, for the cell does not rest. -the nucleus is clearly visible with a distinct nucleoli. -chromosomes appear as irregular granular form, thus cannot be recognized. -consists of three subdivisions: 1st growth period (G1), synthesis period (S), and the 2nd growth period (G2). Interphase: G1 Cell grows; thus, the cell increases in size and in volume. Cells synthesize new proteins. Synthesis of new organelles. Preparation of chromosomes for replication.  Interphase: S phase Most critical period DNA synthesis and replication takes place. RNA and protein synthesis continue Replication of centriole Centriole reproduction begins. Interphase: G2 Completion of DNA synthesis and replication Chromatids duplicate. Prepares the cell to undergo mitosis.  CELL DIVISION: MITOSIS A process that produces two daughter cells with the same quantity and quality of chromosome as the parent cell (identical). Also called duplication division. For growth and repair of body cells. Each cell will receive diploid (2n) number of chromosomes.  Mitosis: Prophase Chromosome starts to coil and become more visible Nucleolus is no longer visible Nuclear membrane starts to disappear Centrioles move to the opposite pole of cell caused by the formation of spindle fiber.  Mitosis: Metaphase Double stranded chromosomes are aligned at the equator of the cell. Kinetochore of each chromosome are attached to the spindle fibers. Nuclear membrane completely disappeared.  Mitosis: Anaphase The continued contraction of spindle fibers separate the sister chromatids. The phase of migration, thus Chromatids move to the opposite poles of the cell. Cytokinesis begins (formation of cell plate in plants and cleavage furrow in animals)  Mitosis: Telophase The phase of Chromatids will start to reconstruction uncoil. Nucleolus reappear Spindle fibers will disappear. New nuclear membrane Cytokinesis completed forms resulting into two daughter Chromatids arrive at the cells with the same quantity opposite poles. and quality of chromosomes as the parent cell.  Meiosis Also known as Reduction-Division. Produces 4 haploid (n) daughter cells. Occurs in germ cells/sex cells to produce gametes. Involves two successive divisions: Meiosis I and II. Why Do We Need Meiosis? Prophase 1 Occupies the longest duration of meiosis. It ensures the variation of the daughter cells. Subdivided into 5 substages: Leptotene Zygotene Pachytene Diplotene Diakinesis  PROPHASE 1 Leptotene- chromosome become more visible than interphase Zygotene- homologous chromosome paired off (synapsis); the pair is referred to as bivalent or tetrad. Pachytene- sharing/ transferring of genetic material between chromatids to ensure that the daughter cells contain gene of both parents, (crossing-over) ; the site of crossing over is “ chiasma”  PROPHASE 1 Diplotene - Synaptonemal complex dissolve. - Recombinant chromosomes. Diakinesis - nuclear envelope and nucleolus disintegrates - centrioles move to opposite poles of the cell -spindle fiber begin to form Homologous chromosomes in a tetrad cross over each other. Pieces of chromosomes or genes are exchanged. Produces Genetic recombination in the offspring.  MEIOSIS I: METAPHASE 1 Homologous pairs of chromosomes align along the equator of the cell  MEIOSIS I: ANAPHASE 1 Homologs separate and move to opposite poles. Sister chromatids remain and attached at their centromeres.  MEIOSIS I: TELOPHASE 1 Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two. MEIOSIS II: REDUCING CHROMOSOME NUMBER Prophase II Metaphase II Anaphase II Telophase II 4 Identical haploid cells  MEIOSIS II: PROPHASE 2 Nuclear envelope fragments. Spindle fibers form. Centrioles starts to move at the opposite poles. Chromosomes are more visible.  MEIOSIS II: METAPHASE 2 Chromosomes align along equator of cell. MEIOSIS II: ANAPHASE 2 Equator Pole Sister chromatids separate and move to opposite poles. MEIOSIS II: TELOPHASE 2 Nuclear envelope assembles. Chromosomes uncoiled. Spindle disappears. Cytokinesis divides cell into two. Cytokinesis Cytoplasm divides Results in 4 haploid (n) daughter cells Chromosomes are unduplicated  RESULTS OF MEIOSIS Gametes (egg & sperm) form Four haploid cells with one copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome 44 GAMETOGENESIS ❖ Spermatogenesis ❖ Oogenesis  SPERMATOGENESIS Creation of sperm cell. Two divisions produce 4 spermatids Spermatids mature into sperm Occurs in testes Men produce about 250,000,000 sperm per day.  OOGENESIS Creation of egg cell. Occurs in the ovaries Two divisions produce 3 polar bodies that die and 1 egg Polar bodies die because of unequal division of cytoplasm Immature egg called oocyte Starting at puberty, one oocyte matures into an ovum (egg) every 28 days.  First polar body may divide a (haploid) X a Polar bodies X a die a X X Mitosis Meiosis I Meiosis II A X (if fertilization Oogonium occurs) A (diploid) Primary X oocyte (diploid) A X Ovum (egg) Mature Secondary A egg oocyte X (haploid) Second polar body (haploid)  COMPARISON OF DIVISIONS Mitosis Meiosis Number of divisions 1 2 Number of daughter 2 diploid cells 4 haploid cells cells Genetically Identical Different Chromosome # Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Function Growth and repair Sexual reproduction Compute for the following: Note: if a parent cell has 20 chromosomes….... 1. How many chromosomes are present in each of the daughter cells after; a. meiosis? b. mitosis? Answer: 1. How many chromosomes are present in each of the daughter cells after; a. meiosis? =10 chromosomes b. mitosis? =20 chromosomes 2. How many centrioles are present during prophase? 3. How many kinetochores are present during prophase? Answer: 2. How many centrioles are present during prophase? =2 centrioles 3. How many kinetochores are present during prophase? =20 kinetochores 4. how many daughter cells will be produced after; a. meiosis? Haploid or Diploid? b. mitosis? Haploid or Diploid? Answer: 4. how many daughter cells will be produced after; a. meiosis? = 4 Haploid or Diploid? b. mitosis? = 2 Haploid or Diploid? 5. how many homologous chromosomes are present during metaphase 1? 6. how many centromeres (kinetochores) are present during anaphase? Answer: 5. how many homologous chromosomes are present during metaphase 1? = 10 homologous chromosomes. 6. how many centromeres (kinetochores) are present during anaphase? =40 kinetochores SEATWORK: 1. If a sex cell has 20 chromatids after Meiosis II, answer the following questions: a. How many chromosomes does the cell have if diploid? b. How many chromosomes does the cell have after Meiosis I? c. How many chromatids does the cell have before Meiosis I? d. How many chromatids does the cell have after Meiosis I? ANSWER: 1. If a sex cell has 20 chromatids after Meiosis II, answer the following questions: a. How many chromosomes does the cell have if diploid? 20 b. How many chromosomes does the cell have after Meiosis I? 10 c. How many chromatids does the cell have before Meiosis I? 40 d. How many chromatids does the cell have after Meiosis I? 20