Cell Cycle & Cell Division - General Zoology 1 (2024-2025 PDF)

General Zoology 1 Porf. Dr. Eman Abbas Moussa Lecturer (2) ahmad ata 1 Cellular Division 2  Cell Division ✓All cells are derived from pre- existing cells ✓New cells are produced for growth and to replace damaged...

General Zoology 1 Porf. Dr. Eman Abbas Moussa Lecturer (2) ahmad ata 1 Cellular Division 2  Cell Division ✓All cells are derived from pre- existing cells ✓New cells are produced for growth and to replace damaged or old cells ✓Differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals) 3  Keeping Cells Identical The instructions for making cell parts are encoded in the DNA, so each new cell must get a complete set of the DNA molecules 4  DNA Replication ✓DNA must be copied or Original DNA replicated strand before cell division Two new, ✓Each new cell identical DNA strands will then have an identical copy of the DNA 5 Identical Daughter Cells Two identical daughter cells Parent Cell 6  Eukaryotic Chromosomes ✓Each chromosome is composed of a single, tightly coiled DNA molecule ✓Chromosomes can’t be seen when cells aren’t dividing and are called chromatin 7  Compacting DNA into Chromosomes ✓DNA is tightly coiled around proteins called histones 8 Chromosomes in Dividing Cells ✓Duplicated chromosomes are called chromatids & are held together by the centromere Called Sister Chromatids 9  Boy or Girl? The Y Chromosome Decides Y - Chromosome X - Chromosome 10 Cell Reproduction 11  Types of Cell Reproduction ✓Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells ✓Mitosis & binary fission are examples of asexual reproduction ✓Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells ✓Meiosis is an example 12 Five Phases of the Cell Cycle ✓G1 - primary growth phase ✓S – synthesis; DNA replicated ✓G2 - secondary growth phase collectively these 3 stages are called interphase ✓M - mitosis ✓C - cytokinesis 13 Cell Cycle 14 Interphase - G1 Stage ✓1st growth stage after cell division ✓Cells mature by making more cytoplasm & organelles ✓Cell carries on its normal metabolic activities 15  Interphase – S Stage ✓Synthesis stage ✓DNA is copied or replicated Two identical copies of DNA Original DNA 16  Interphase – G2 Stage ✓2nd Growth Stage ✓Occurs after DNA has been copied ✓All cell structures needed for division are made (e.g. centrioles) ✓Both organelles & proteins are synthesized 17 What’s Happening in Interphase? What the cell looks like Animal Cell What’s occurring 18  Sketch the Cell Cycle DNA Copied Cells prepare for Cells Division Mature Daughter Cells Cell Divides into Identical cells 19  Mitosis ✓Division of the nucleus ✓Also called karyokinesis ✓Only occurs in eukaryotes ✓Has four stages ✓Doesn’t occur in some cells such as brain cells 20  Four Mitotic Stages ✓Prophase ✓Metaphase ✓Anaphase ✓Telophase 21  Early Prophase ✓Chromatin in nucleus condenses to form visible chromosomes ✓Mitotic spindle forms from fibers in cytoskeleton or centrioles (animal) Nucleolus Cytoplasm Nuclear Membrane Chromosomes 22  Late Prophase ✓Nuclear membrane & nucleolus are broken down ✓Chromosomes continue condensing & are clearly visible ✓Spindle fibers called kinetochores attach to the centromere of each chromosome ✓Spindle finishes forming between the poles of the cell 23  Late Prophase Chromosomes Nucleus & Nucleolus have disintegrated 24  Spindle Fiber attached to Chromosome Kinetochore Fiber Chromosome 25  Spindle Fibers ✓The mitotic spindle form from the microtubules in plants and centrioles in animal cells ✓Polar fibers extend from one pole of the cell to the opposite pole ✓Kinetochore fibers extend from the pole to the centromere of the chromosome to which they attach ✓Asters are short fibers radiating from centrioles 26  Metaphase ✓Chromosomes, attached to the kinetochore fibers, move to the center of the cell ✓Chromosomes are now lined up at the equator Equator of Cell Pole of the Cell 27  Review of Metaphase What the cell looks like What’s occurring 28  Anaphase ✓Occurs rapidly ✓Sister chromatids are pulled apart to opposite poles of the cell by kinetochore fibers 29  Anaphase Review What the cell looks like What’s occurring 30  Telophase ✓Sister chromatids at opposite poles ✓Spindle disassembles ✓Nuclear envelope forms around each set of sister chromatids ✓Nucleolus reappears ✓CYTOKINESIS occurs ✓Chromosomes reappear as chromatin 31 Comparison of Anaphase & Telophase 32  Cytokinesis ✓Means division of the cytoplasm ✓Division of cell into two, identical halves called daughter cells ✓In plant cells, cell plate forms at the equator to divide cell ✓In animal cells, cleavage furrow forms to split cell 33  Cytokinesis Cleavage furrow Cell plate in in animal cell plant cell 34  Daughter Cells of Mitosis ✓Have the same number of chromosomes as each other and as the parent cell from which they were formed ✓Identical to each other, but smaller than parent cell ✓Must grow in size to become mature cells (G1 of Interphase) 35 Identical Daughter Cells What is the 2n or diploid number? 2 Chromosome number the same, but cells smaller than parent cell 36  Meiosis Formation of Gametes (Eggs & Sperm) 37  Facts About Meiosis ✓Preceded by interphase which includes chromosome replication ✓Two meiotic divisions --- Meiosis I and Meiosis II ✓Called Reduction- division ✓Original cell is diploid (2n) ✓Four daughter cells produced that are monoploid (1n) 38  Facts About Meiosis ✓Daughter cells contain half the number of chromosomes as the original cell ✓Produces gametes (eggs & sperm) ✓Occurs in the testes in males (Spermatogenesis) ✓Occurs in the ovaries in females (Oogenesis) 39  More Meiosis Facts ✓ Startwith 46 double stranded chromosomes (2n) ✓After 1 division - 23 double stranded chromosomes (n) ✓After 2nd division - 23 single stranded chromosomes (n) ✓ Occurs in our germ cells that produce gametes 40 Why Do we Need Meiosis? ✓It is the fundamental basis of sexual reproduction ✓Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote 41 Fertilization – “Putting it all together” 2n = 6 1n =3 42  Replication of Chromosomes ✓Replication is the process of duplicating a Occurs in chromosome Interphase ✓Occurs prior to division ✓Replicated copies are called sister chromatids ✓Held together at centromere 43  Meiosis: Two Part Cell Division Sister chromatids Homologs separate separate Meiosis Meiosis I II Diploid Diploid Haploid 44  Meiosis I: Reduction Division Nucleus Spindle fibers Nuclear Early envelope Prophase I Late Metaphase (Chromosome Prophase I Anaphase Telophase I number I I (diploid) doubled) 45  Prophase I Early prophase Late prophase ✓Homologs pair. ✓Chromosomes condense. ✓Crossing over ✓Spindle forms. occurs. ✓Nuclear envelope fragments. 46 Tetrads Form in Prophase I Homologous chromosomes Join to form a (each with sister TETRAD chromatids) Called Synapsis 47  Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment 48 Metaphase I Homologous pairs of chromosomes align along the equator of the cell 49 Anaphase I Homologs separate and move to opposite poles. Sister chromatids remain attached at their centromeres. 50 Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two. 51  Meiosis II: Reducing Chromosome Number Prophase Metaphase II Telophase II Anaphase II 4 Genetically II Different haploid cells 52 Prophase II Nuclear envelope fragments. Spindle forms. 53 Metaphase II Chromosomes align along equator of cell. 54  Anaphase II Equator Pole Sister chromatids separate and move to opposite poles. 55 Telophase II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two. 56 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 57 Gametogenesis Oogenesis or Spermatogenesis 58  Spermatogenesis ✓Occurs in the testes ✓Two divisions produce 4 spermatids ✓Spermatids mature into sperm ✓Men produce about 250,000,000 sperm per day 59 Spermatogenesis in the Testes Spermatid 60  Oogenesis ✓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 61 Oogenesis in the Ovaries 62 Comparing Mitosis and Meiosis 63  Comparison of Divisions Mitosis Meiosis Number of 2 1 divisions Number of 2 4 daughter cells Genetically Yes No identical? Chromosome # Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Growth and Role Sexual reproduction repair 64