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Understanding Chromosome Structure and Cell Division in Biology

Learn about chromosomes' rod-shaped structures, histones, chromatids, karyotypes, and cell division in prokaryotes and eukaryotes. Discover the cell cycle stages, mitosis steps, and checkpoints.

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Understanding Chromosome Structure and Cell Division in Biology

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  1. Cell Reproduction Chapter 8 Biology CPA

  2. Chromosomes • Rod shaped structures made of DNA and proteins • Chromosomes are visible in cells undergoing division • Chromosomes are made by DNA coiling into tight structures • Consist of two identical halves

  3. Chromosome Structure • Histones are proteins that DNA wraps around to make the chromosome shape • Chromosomes are made of two sister chromatids • Identical to each other

  4. Chromosome Structure • Each chromosome is made of two “sister” chromatids • Near center of the chromosome is the centromere • Chromosomes are tightly coiled strings of DNA called chromatin

  5. Chromosome Numbers • There is a specific numberof chromosomes in each organism • Ex: Humans have 46, chimpanzees have 48 • Humans have autosomesand sexchromosomes • We have 2 sex chromosomes • Either X or Y • We also have 44 autosomes • Which do not code for gender

  6. Chromosome Numbers • Every cell of an organism produced by sexual reproduction has two copies of each autosome • One copy from mom and one copy from dad • The two copies of each pair is called homologous chromosomes • Same size and shape • Carry genes for the same traits

  7. Karyotype • A karyotype is a pictureof one set of chromosomes • Shows you sex of organism • Shows your any chromosomal disorders

  8. Chromosome Numbers • A diploidcell contains 2 sets of each chromosome • Prefix di = 2 • Abbreviated as 2n • n = number of chromosomes • A haploidcell contains only 1 set of each chromosome • Half of the total number • Usually sexcells

  9. Cell Division in Prokaryotes • Prokaryotes • No nucleus • No organelles • Ex: Bacteria • Reproduction is very fast • Copy DNA • Split into twoidentical daughter cells • Cell division is calledbinaryfission

  10. Cell Division in Eukaryotes • Eukaryotes • Have a nucleus • Have organelles • Ex: Humans, plants • Both nucleus and cytoplasm need to divide • Process of making new cells is called mitosis • Makes twoidentical daughter cells • Complex reproduction • Everything needs to be regulated! • Much more complex process – about 18 hours!

  11. Cell Division and Reproduction • Asexual Reproduction • Produces identicaloffspring from a singleparent • Used by many single-celled organisms • Ex: bacteria • Occurs very quickly • Sexual Reproduction • Produces genetically differentoffspring from two parents • Fusion of two parent cells • Creates haploidgametes (sex cells)

  12. The cell Cycle • A repeating set of events in the life of a cell • A cell splits to make 2 identicalcopies • This occurs in 3 main stages • Interphase – growth • Mitosis – divisionof the cell • Cytokinesis – Splitting of the cytoplasm

  13. Interphase • Cell growth • Majority of cell’s life span is spent in this phase • 3 Part of Interphase: • G1, S, G2

  14. G1 Phase • Gap 1 Phase • The cell is growing to mature size

  15. S Phase • S = synthesisof DNA • DNA is copiedso there is a set for each new cell

  16. G2 Phase • Gap 2 Phase • Cell growsagain • Replication of organelles • Cell prepares for cell division

  17. mitosis Cell Division

  18. mitosis • The part of a cell’s life cycle when the cell’s nucleus divides into 2 identicalnuclei • 4 steps: • Prophase • Metaphase • Anaphase • Telophase

  19. Prophase • Shortening and tight coiling of chromatin into chromosomes • Nucleus breaks down and disappears • Centrioles separate and move to opposite poles of the cell • Centrosomes in plant cells • Centrioles shoot off spindlefibers

  20. metaphase • Spindle fibers are connected to centromere of chromosomes • Spindle fibers move chromosomes • Chromosomes line up at the equator of the cell • Chromosomes are in the MIDDLE

  21. anaphase • Sister chromatids attach to the short spindlefibers • Chromatids of each chromosome separate at the centromere • Chromosomes are pulled APART • Spindle fibers shorten and bring the sister chromatids to oppositepoles • After chromatids separate, they are called individual chromosomes

  22. Telophase • Chromatids become chromatin • Spindle fibers disassemble • Nuclear envelope forms around each set of chromatin • Nucleolus reappears

  23. Cytokinesis • Once mitosis has finished! • Last stage of cellcycle • Process is when the cytoplasm splits apart

  24. Cytokinesis in Plant Cells • A cellplateforms between the two nuclei • The cytoplasm divides • A cellwallforms two daughter cells

  25. Cytokinesis in Animal Cells • Cell membrane pinches in at equator • Cleavage furrow

  26. Cells in Various Stages of the Cell Cycle

  27. Control of Cell Division • Checkpoints (Regulatory Proteins) • Repair enzymes fix any mutations • G1 Checkpoint • Proteins check to see if cell will be able to divide • Check for cell size • G2 Checkpoint • DNA repair enzymes check results of DNA replication during S phase • Mitosis checkpoint • If all is correct, proteins will signal cell to exit mitosis • Cell will renter interphase after cytokinesis and start process over again • If a cell does not meet requirements for checkpoints, the cell will be programmed to die • Apoptosis is controlled cell death

  28. Uncontrolled Mitosis is cancer.

  29. When Control is Lost • Enzyme proteins are not functioningproperly causing cell to reproduce outofcontrol • Could cause cancer • Cancer cells do not respond to body’s regulators that control mechanisms • A mass of cancer cells is called a tumor

  30. Compare/Contrast

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