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Theme: Reproduction on a cellular level L ecturer : prof. Fedonyuk L.Ya.

Theme: Reproduction on a cellular level L ecturer : prof. Fedonyuk L.Ya. Plan of lecture:. Structure of nucleus The levels of organization of eukariotic chromosomes. С hromosomes types. Normal human karyotype characteristics. Cell (mitotic) cycle, its stages. Mitosis, its stages.

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Theme: Reproduction on a cellular level L ecturer : prof. Fedonyuk L.Ya.

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  1. Theme: Reproduction on a cellular levelLecturer: prof. Fedonyuk L.Ya.

  2. Plan of lecture: • Structure of nucleus • The levels of organization of eukariotic chromosomes. • Сhromosomes types. • Normal human karyotype characteristics. • Cell (mitotic) cycle, its stages. Mitosis, its stages. • Cytological and cytogenetically characteristics of meiosis.

  3. Nucleus consists of • nuclear envelope • nucleolus • nucleoplasm • chromatin (chromosomes)

  4. Nuclear envelope • surrounds the nuclear material • consists of two parallel membranes separated from each other by a narrow perinuclear cisternae • is perforated at intervals by openings called nuclear pores

  5. Nuclear Membrane or Envelope - two membranes which form the nucleus, is porous. Allows RNA to leave nucleus.

  6. Assembly and Disassembly of Nuclear Envelope • Nuclear envelope is a cell cycle dependent structure that disperses at the onset of mitosis (late prophase) and reassembles around the reforming nucleus in the late telophase. • The correlations of breakdown of the nuclear envelope, formation of chromosomes and mitosis are essential for cell division and the ability of cells to divide in an orderly manner.

  7. Nucleoplasm • is the portion of the protoplasm that is surrounded by the nuclear envelope • is consists of a matrix and various types of particles.

  8. Whole Mount Electron Microscopy Demonstrating Fibrogranular Structure of the Internal Nuclear Matrix

  9. Nucleolus • is a well-defined nuclear inclusion (sometime more than one) • is present in the cells that are actively synthesizing proteins • become detectably only when the cell is in interphase • is involved in the synthesis of rRNA and its assembly into precursors of ribosomes

  10. Chromatin • is double-stranded DNA complexed with histones and acidic proteins • is responsible for RNA – synthesis, resides within the nucleus in two forms: heterochromatin and euchromatin

  11. Heterochromatin • is a highly condensed portion of chromatin • is visible in light microscope • appears in the light microscope as basophilic clumps of nucleoprotein • is not transcribed into RNA

  12. Euchromatin • isn’t condensed portion of chromatin during interphase • from which RNA is transcribed, its genes can be activated, is transcriptionally active, mostly encodes proteins • does not visible in light microscope.

  13. Levels of organization of eukaryotic chromosomes: 1. The DNA is associated with basic proteins called histones to form nucleosomes, each of which consists of 8 histones bead with DNA wrapped around it. 2. The nucleosomes are organized into large coiled loops held together by nonhistone scaffolding proteins. 3. The chromonema is a single double-stranded DNA molecule with a protein coat

  14. Chromosome = DNA (deoxyribonucleic acid) + associated proteins (mainly histones) = “packaged” DNA

  15. Organization of eukaryotic chromosomes • The chromosomes have already doubled, and each now consists of two identical sister chromatid • The chromatid is composed of a very fine filament, called as chromonema • The two chromatids remain attached to each other at a point of primary constriction, the centromere. • The centromere is a specific DNA sequence of about 220 nucleotides, to which is bound a disk of protein called a kinetochore. • It is a place, where the spindle fibers attach during cell division. • Regions on either sides of centromere are called arms. • The long arm of a chromosome is designated “q” and the short arm – “p”.

  16. Metaphase chromosome structure 1 - long arm 2 - short arm 3 - centromere 4 - secondary constriction 5 - satellite 6 - chromatids

  17. Types of chromosomes 1 – Metacentric (the centromere divides it into two equal arms) 2 – Submetacentric (the centromere is slightly displace from the center of chromosome) 3, 4 – Acrocentric (the centromere establishes one long arm and one short arm) а – centromere б - secondary constriction

  18. Karyotype • is a diploid number of chromosomes • is represented in humans by the 22 pairs of autosomes and the 1 pair of sex chromosomes (either XX or XY) totaling 46 chromosomes • Pair of chromosomes, with the same gene loci in the same order, are known as the homologous chromosomes. • The chromosomes of each pair have characteristic size and shape. • An ideogram is a karyotype, which displays chromosomes arranged in pairs in descending size order. • 2n=44a+XX(femalekaryotype) • 2n=44a+XY(malekaryotype)

  19. Two important characters of living organisms, Growth and Reproduction are due to Cell division. • Cell division involves two phases • 1. Division of nucleus. • 2. Division of cytoplasm. • Two major types of cell division • 1. Mitosis - similar daughter cells (2n) • 2. Meiosis - Haploid/gametes (n)

  20. The cell cycle • Covers a time from one division of cells till other division or destruction (perish) of cell • It has two major stages: • 1)mitosis • 2) interphase

  21. Cell Cycle: Interphase • Before mitosis • Time of high metabolic activity • DNA replicated and synthesized • Three phases: G1, S, and G2 • G1(gap 1)- longest stage of cell cycle, RNA, protein sysnthesis • S (synthesis)- DNA replicated , 2 chromatids per chromosome, chromatids genetically identical • G2(gap 2)- RNA synthesis, not well understood

  22. Thehuman cell cycle DNA synthesis synthesis S phase G1 phase Rapid growth and preparation for DNA synthesis G2 phase Growth and preparation for cell division M phase Mitosis

  23. Cell Cycle: Mitosis • Process of cell division(nuclear division) which produces daughter cells genetically identical to the parent cell • Four Phases (P-M-A-T): prophase, metaphase, anaphase, and telophase. • Upon completion of the phases of mitosis (nuclear division) the cell “officially” divides into two by a process called cytokinesis - division of cytoplasm

  24. Cell Cycle

  25. Interphase Not part of mitosis DNA is replicated chromosomes start to condense

  26. Chromosome duplication

  27. Prophase *Chromosomes coil and condense further. *Nucler membrane breaks down/ disappears. *Microtubules increase in number, spindle apparatus forms.

  28. G2, Prophase

  29. Metaphase *Nuclear membrane completely disappeared *Chromosomes move to equator of cell - begin to line up *Chromosomes attach to spindle via kinetochore

  30. Centromeric Region

  31. Anaphase *Movement of chromosomes via microtubules to opposite sides of the cell. One chromatid to one end the other Chromatid to the opposite end

  32. Chromatid Separation

  33. In anaphase, the sister chromatids separate. • Two daughter cells • Each has a complete and identical set of chromosomes

  34. Telophase *Genetically identical info at each pole *Spindle fibers disappear *Chromosomes uncoil *Nuclear envelope reforms around

  35. Metaphase, Anaphase, Telophase METAPHASE ANAPHASE Metaphaseplate Nuclearenvelopeforming Spindle Daughterchromosomes

  36. Mitosis in a plant cell

  37. Cytokinesis Cytokinesis - is separate from mitosis, = pinching of cell/divison of cytoplasm. Mitosis + Cytokinesis result in two identical daughter cells.

  38. Mitosis

  39. Histologic picture of Mitosis:

  40. Mitosis: • Interphase: No morphological changes, Replication of DNA and organelles. • Prophase: Visible chromosomes • Metaphase: equatorial plate formation • Anaphase: Separation of chromosome pairs • Telophase: Two separate nuclei formation. • Cytokinesis: Separation of daughter cells.

  41. Chromosomes and Chromatids During Mitosis

  42. Cell division

  43. Molecular Basis of Carcinogenesis • Genes control cell division by cytokines. • Four classes of regulatory genes. • Promotors – Proto-oncogenes • Inhibitors – Cancer-suppressor genes – p53 • Genes regulating Apoptosis. • DNA repair genes.

  44. Meiosis • Cell division which results in halpoid “sex” cells (i.e., egg and sperm) • One replication of the genetic material (DNA) during interphase, but two nuclear divisions (meiosis I and meiosis II). • Results in haploid (N) cells (= gametes in animals) from an initial diploid (2N) cell • Very similar to mitosis except that the cells produced are not genetically identical.

  45. Overview of meiosis: how meiosis reduces chromosome number

  46. Meiosis Meiosis I (reduction) Prophase I is divided into the following five stages: • Leptotene -the chromatin condenses into the visible chromosomes, each of which contain two chromatids joined at the centromere • Zygotene - homologous maternal and paternal chromosomes pair and make physical contact (synapsis), forming a tetrad

  47. Crossing-Over

  48. . Prophase I • Pachytene -the chiasmata are formed and crossing over (random exchanging of genes between segments of homologous chromosomes) occurs – an event that is crucial for increasing generic diversity • Diplotene - the chromosomes continue to condense and chiasmata can be observed, indicating where crossing over has taken place • Diakinesis - the nucleolus disappears, chromosomes are condensed maximally, and the nuclear envelope disappears

  49. Metaphase I • Spindle formation is complete • Bivalents are aligned at equator • Kinetochore microtubules of the homologues point to opposite poles Anaphase I • Homologues separate and move toward opposite poles • Cytokinesis begins

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