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Concept 9.1

Concept 9.1. ALL CELLS COME FROM CELLS. CELL REPRODUCTION. “ All cells come from pre-existing cells” Two main types of cell reproduction: Asexual : ( MITOSIS ) – cells make identical copies of themselves Sexual : ( MEIOSIS ) – produces gametes (sperm and egg cells). SIMPLE CELL DIVISION.

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Concept 9.1

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  1. Concept 9.1 ALL CELLS COME FROM CELLS

  2. CELL REPRODUCTION • “All cells come from pre-existing cells” • Two main types of cell reproduction: • Asexual: (MITOSIS) – cells make identical copies of themselves • Sexual: (MEIOSIS) – produces gametes (sperm and egg cells)

  3. SIMPLE CELL DIVISION • Simple cell division: process used for asexual cell reproduction • One parent cell produces two daughter cells • Both daughter cells are genetically identical to parent cell

  4. FUNCTIONS OF SIMPLE CELL DIVISION • For unicellular organisms: mechanism for reproduction • For multicellular organisms: mechanism for growth, repair, development, and renewal

  5. SEXUAL REPRODUCTION • Involves two parents and the union of gametes (sex cells) • Offspring not identical to either parent • Offspring have a combination of genetic material from each parent • Special type of cell division is needed to produce gametes (discussed later)

  6. Concept 9.2 THE CELL CYCLE MULTIPLIES CELLS

  7. CHROMOSOMES & CELL DIVISION • Chromatin: long thin fibers made up of DNA & protein molecules in nucleus • Not visible with light microscope • Chromosome: condensed chromatin threads formed when cell prepares to divide • Visible with light microscope

  8. THE CELL CYCLE • Sequence of growth and division of cell • Extends from “birth” of cell to the time that a cell reproduces itself • Two general periods: 1.interphase – growth of the cell 2. mitosis – division of the nucleus of cell

  9. INTERPHASE • Longest phase of cell cycle • Cell increases supply of proteins, organelles, and grows in size • Divided into 3 phases: G1, S, and G2

  10. CELL CYCLE OVERVIEW

  11. G1 PHASE • Cell grows rapidly in size • Metabolic activity is high • Preparation for DNA replication • Duplication of organelles

  12. S PHASE • Synthesis phase • DNA synthesis takes place • Duplicate copies of each chromosome are made

  13. G2 PHASE • Shorter than G1 • Cell grows • Duplication of organelles • Preparation for cell division

  14. MITOTIC (M) PHASE • Consists of two processes: • Mitosis (M): duplicated chromosomes divide and separate to form two “daughter” nuclei • Cytokinesis (C): cytoplasm is divided

  15. Concept 9.3 CELLS DIVIDE DURING THE MITOTIC PHASE

  16. MITOTIC SPINDLE • Separation of chromosomes is guided by the spindle football-shaped framework of microtubules • Spindle microtubules grow from two centrosomes • Centrosomes: regions of material in cytoplasm—in animals, they contain structures called centrioles

  17. PHASES OF MITOSIS • Divided into 4 phases: PMAT 1st - Prophase 2nd - Metaphase 3rd – Anaphase 4th - Telophase and Cytokinesis

  18. Chromatin coils into visible chromosomes  sisterchromatids Nucleolus disappears Nuclear membrane breaks down Mitotic spindle forms from centrioles Spindle fibers attach to centromeres of sister chromatids PROPHASE

  19. Sister chromatids: pairs of identical chromosomes created before a cell divides Centromere: region where two sister chromatids are joined together SISTER CHROMATIDS

  20. Chromosomes line up at equator or midline of cell Each consists of identical sister chromatids Spindle fibers attach to centromeres METAPHASE

  21. Sister chromatids separate from their partners Each chromatid is now considered to be a daughter chromosome Chromosomes are pushed and pulled to opposite poles ANAPHASE

  22. Events of prophase are reversed: Spindle disappears Nuclear envelopes reform around daughter chromosomes Chromosomes uncoil and lengthen forming chromatin Nucleolus reappears in each new nucleus TELOPHASE

  23. CYTOKINESIS • Division of cytoplasm—usually occurs along with telophase • Occurs by different mechanisms in animal and plant cells • Animal cells: formation of a cleavagefurrow separates two new nuclei • Plants cells: formation of cell plate

  24. ANIMAL CELL PLANT CELL CYTOKINESIS

  25. Clockwise from top: Interphase Prophase Metaphase Anaphase Telophase and cytokinesis INTERPHASE & MITOSIS

  26. MITOSIS OVERVIEW

  27. MITOSIS: REVIEW & QUIZ

  28. MITOSIS & CYTOKINESIS

  29. Concept 9.4 CANCER CELLS GROW AND DIVIDE OUT OF CONTROL

  30. “CONTROL SYSTEMS” IN CELL DIVISION • Enzymes control sequence of events in the cell cycle • Malfunctions in the control system may cause cells to reproduce at the wrong time or in the wrong place

  31. TUMORS & CANCER • Benign tumor: abnormal mass of essentially normal cells • Always remain at original site • May cause health problems depending on size and location • Can usually be surgically removed

  32. TUMORS & CANCER • Malignant tumors: masses of cells that result from reproduction of cancer cells • Cancer: disease caused by disruption of mechanisms that control the cell cycle • Metastasis: spread of cancer cells beyond original site • Most dangerous characteristic is the ability of cancer cells to spread to different areas of body

  33. CANCER TREATMENT • Surgery: malignant tumor removed • Radiation & Chemotherapy: used to disrupt cell division • May have undesirable side effects

  34. Concept 9.5 MEIOSIS FUNCTIONS IN SEXUAL REPRODUCTION

  35. MEIOSIS • Type of cell division that produces four cells • Each new cell has half the number of chromosomes as the parent cell • Meiosis produces gametes sperm and egg cells • In animals, meiosis occurs in the sex organs—ovaries and testes

  36. HUMAN CHROMOSOMES • Humans have 23 pairs of homologous chromosomes • Females: all 23 pairs look alike • Males: two chromosomes of one pair do not look alike • Sex chromosomes: pair of chromosomes that determine sex • Occur in two forms: X and Y • Females: XX and Males: XY

  37. Paired chromosomes: one inherited from the mother and the other from the father Not identical to one another Each has same genes controlling the same trait in same order HOMOLOGOUS CHROMOSOMES

  38. Karyotype: a display of 46 chromosomes of an individual Human body cells  46 chromosomes—23 pairs of homologous chromosomes Each chromosome has a twin that resembles it in size and shape(except sex chromosomes in males) KARYOTYPES

  39. HUMAN KARYOTYPES

  40. DIPLOID & HAPLOID CELLS • Diploid:(2n) contain two homologous sets of chromosomes  46 total • Body (somatic) cells -most human cells are diploid • Haploid: (n) have a single set of chromosomes  23 total • Gametes - sperm and egg – are haploid

  41. Fertilization: fusing of the nucleus of a haploid sperm with the nucleus of a haploid egg • Zygote: produced as a result of fertilizationfertilized egg is diploid

  42. PROCESS OF MEIOSIS • Two distinct parts: • Meiosis I: homologous chromosomes separate from each other - sister chromatids remain together • Meiosis II: sister chromatids separate from each other

  43. Process begins just like mitosis Interphase: cell duplicates its DNA Meiosis begins after chromosomes have been duplicated MEIOSIS I

  44. Similar to prophase in mitosis Chromatin coils up Nuclear membrane disappears Nucleolus disappears Spindle fibers attach to only one side of centromere PROPHASE I

  45. Has two steps not seen in prophase of mitosis 1. Tetrad Formation 2. Crossing Over PROPHASE I

  46. TETRAD FORMATION • Homologous chromosomes—one from each parent—line up along their length gene by gene and pair tightly • Tetrad: four part structure—made up of two homologous chromosomes, each made up of two sister chromatids

  47. Chromosomes in tetrad are tightly paired Non-sister chromatids (each from a different parent) can fold over each other, break, and exchange genetic material CROSSING OVER

  48. Homologous chromosomes line up together as tetrads at midline of cell This step is unique to meiosis Homologous chromosomes line up independently of one another in mitosis METAPHASE I

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