The cell cycle

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Mitosos and Meiosis

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The cell cycle

  1. 1. ULTRASTRUCTURE OF CELLS
  2. 2. OBJECTIVES • Identify the cell organelles and their respective functions • Recognize the differences of bacterial, plant, and animal cells • Appreciate importance of cells to an organism • Prepare fresh mounts of kinds of cells
  3. 3. PLANT CELL • cell wall • cell membrane • nucleus • cytoplasm • vacuole
  4. 4. ANIMAL CELL • cell nucleus • cytoplasm
  5. 5. BACTERIAL CELL • movement – jerky • rod shaped
  6. 6. FUNGAL CELLS • sporangium • sporangiophore (hyphae) • rhizoid • stolon
  7. 7. COMPARISON • Size • Shape • Protective covering • Organelles
  8. 8. THE CELL CYCLE
  9. 9. CHROMOSOME NUMBER • all organisms contain chromosome where genes are found • thread-like structures in a cell’s nucleus visible under microscope only during cell division • somatic cells (non-reproductive body cell) has a partner chromosome occurring in pairs • homologous chromosomes - two members of a pair chromosome • diploid – chromosomes occurring in pairs (2n) • haploid – single set of unpaired chromosome (n)
  10. 10. AUTOSOMES VS SEX CHROMOSOMES • sex determination is based on sex chromosomes • a pair containing 2 X chromosomes would entail female sex and 1 X and O would entail male sex
  11. 11. THE CELL CYCLE • period from beginning of one division to the beginning of the next division • generation time – the period between two successive divisions/complete revolution of the cycle • 8 to 20 hours
  12. 12. CELL CYCLE S Phase • DNA synthesis • 10-12 hours • each replicated DNA molecules intertwine held tightly together by a protein M Phase • chromosome segregation and cell division • lesser time • major events: nuclear division and cytoplasmic division
  13. 13. G1 PHASE AND G2 PHASE • G1 phase is between M-phase and S-phase • G2 phase is between S-phase and Mitosis • time delays to allow cell growth • monitor internal and external environment • G1 – if external conditions are unfavorable, it extends to form the G0 phase
  14. 14. CELL CYCLE CONTROL SYSTEM
  15. 15. G1 PHASE AND G2 PHASE G1 Phase • event between the previous cell division and DNA replication • cell grows • longest phase • synthesis of certain enzymes used in DNA replication G2 Phase • increased protein synthesis for preparation in cell division • short phase • beginning of mitosis marks the end of G2
  16. 16. INTERPHASE • period of active growth and maintenance after mitosis • synthesizes needed materials • grows • chromosomes undergo duplication
  17. 17. LOCATION OF MITOSIS • meristems (meristo “divided”) • shoot and root tips (apical meristems) • thin cylindrical regions that run the entire lengths of the stems and roots (lateral meristems) • temporary meristems are produced when a plant is wounded or encounters a disease
  18. 18. LOCATION OF MITOSIS
  19. 19. MITOSIS
  20. 20. PROPHASE • chromatin (long, thin, thread (like material of which chromosomes are composed) condense and coil into visible chromosome • chromosomes become shorter and thicker • centromere – constricted region • kinetochore – attached to the centromere where microtubules bind
  21. 21. PROPHASE • nuclear envelope disappears and breaks apart • the nucleolus shrinks • microtubules organize between poles to form the mitotic spindle (aids in movement of chromosome)
  22. 22. METAPHASE • short period of chromosomes lining up in the midplane of the cell • mitotic spindle (visible and made up of microtubules extending from pole to pole)
  23. 23. ANAPHASE • once chromatids are no longer attached to their duplicates they are considered independent chromosomes • chromatids move to opposite poles
  24. 24. TELOPHASE • final stage of mitosis • chromosomes arrive to the poles and return to their interphase condition • new nuclear envelope forms • nucleoli reorganizes • spindle fiber disappears
  25. 25. CYTOKINESIS • division of the cytoplasm • begins during telophase • cell plate → plasma membrane and cell walls
  26. 26. MEIOSIS
  27. 27. SEXUAL REPRODUCTION • reproductive cells (eggs and sperm cells) are called gametes • half the diploid number of chromosome • form a complete new organism by uniting • ♀ gamete (egg) unites with the ♂ gamete (sperm) = zygote (fertilized egg)
  28. 28. MEIOSIS • type of cell division that reduces the number chromosomes in reproductive cells by half • “to make smaller” • haploid cells always contain each homologous pair • when two numbers of haploid cells unite during fertilization, the normal diploid number of the cell is restored
  29. 29. PROPHASE I • elongated and thin homologous chromosomes lie side by side (synapsis) • crossing over – pieces of maternal and paternal chromatids break off and rejoined to the opposite chromatid; produces new combination of genes • genetic recombination – enhances variety among sexually produced offspring
  30. 30. PROPHASE I
  31. 31. METAPHASE I • homologous chromosomes line up in pairs along the midplane
  32. 32. ANAPHASE I • homologous chromosome separate with one moving toward one pole and the other toward the other pole • chromosomes remain united at centromere
  33. 33. TELOPHASE I • duplicated chromosome (one of each homologous pair) at each pole
  34. 34. MEIOSIS II
  35. 35. PLANT LIFE CYCLE • diploid plant (sporophyte) produces haploid spores by meiosis • Spores divide by mitosis to give rise to a multicellular plant known as gametophyte whose cells all contain haploid number of the chromosomes
  36. 36. SPERMATOGENESIS & OOGENESIS • spermatogenesis • produces mature sperm cells • all four products can acquire a flagellum for locomotion and a cap-like structure that aid in the penetration of the cell • oogenesis • production of mature ovum or egg cell • only one of four meiotic products develops into functional gamete
  37. 37. BRING THE FOLLOWING • Onion root tips • prepare by placing in a vial containing 70% ETHYL alcohol • glass slide, cover slips • gillette blade or scalpel • check flies next meeting

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