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1.3 Cell Division

1.3 Cell Division. Where do cells come from?. All cells come from other cells in order for this to happen, cells must divide. Why is cell division important?. 1. Growth cells must divide in order to maintain a high surface area

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1.3 Cell Division

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  1. 1.3 Cell Division

  2. Where do cells come from? All cells come from other cells • in order for this to happen, cells must divide

  3. Why is cell division important? 1. Growth • cells must divide in order to maintain a high surface area • allows for many access points for nutrients to enter & wastes (CO2) to leave the cell • the distance from the nucleus to all parts of the cell must be kept small so messages can be relayed quickly 2. Repair • dead cells need to be replaced 3. Reproduction • unicellular organisms can create 2 organisms • multicellular organisms can repair & grow

  4. The Cell Cycle • Cells alternate between stages of growth and division • growth = interphase • division = mitosis • Most of a cell’s life is spent in interphase • Only a small portion of its cycle is cell division, aka mitosis (& cytokinesis)

  5. Mitosis • The process where (the nucleus of) new cells form from other cells • Two exact copies (of the nucleus) are made by doubling one cell’s genetic material (DNA) pronounced my-TOE-sis

  6. Cell Division • process where one (parent) cell divides to make two (daughter) cells • in multicellular organisms like humans, this is: • how a fertilized egg becomes an adult with trillions of cells • how we replace damaged cells

  7. Let’s review… (just a little)

  8. Limiting Cell Size • a cell can’t get too big or it will not have enough surface area for the passage of: • nutrients it needs in the cell (O2, H2O, Na1+, Ca2+, …) • wastes it produces out of the cell (CO2, H2O, K1+, …) • this is why when cells get to be a certain size, they must divide to survive! The greater the surface area, the easier it is for a cell to function

  9. The bottom line: • Cells must divide in order to remain small so: • messages can be transmitted quickly • diffusion (of nutrients) can get happen quickly • wastes can be sent out of the cell quickly

  10. So, what do mitosis & cytokinesis really mean? mitosis = the division of a cell’s nucleus into two equal parts cytokinesis = the division of the cytoplasm & the rest of the cell’s organelles to form 2 daughter cells • happens after mitosis

  11. The Cell Cycle

  12. What happens during interphase? 1. Cell grows 2. DNA doubles • parent cell must make a copy of its genetic info before it divides so that each daughter cell will get a complete set of chromosomes • chromosomes, which are normally thin thread-like structures, thicken • each chromosome is duplicated, making sisterchromatids • chromatid = thickened, duplicated chromosomes chromatin = term used to describe thin, thread-like chromosomes

  13. DNA replication

  14. The 4 phases of mitosis: PMAT • Remember, mitosis actually involves just the nucleus • contents of the nucleus double • the nucleus divides into two equal parts • 4 phases: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

  15. Phase 1: Prophase • Sister chromosomes coil & condense • Chromosomes become visible (now officially called chromatids) • Membrane around the nucleus dissolves • Nucleolus disappears • Organelles called centrosomes head to opposite ends of the cell & begin to form structures called spindle fibres (which help with cell division)

  16. Phase 2: Metaphase • Chromosomes line up in the middle of the cell • Spindle fibres are completely formed and stretch from one side of the cell to the other • Chromosomes attach to spindle fibres, special structures that help chromosomes move

  17. Phase 3: Anaphase • Sister chromosomes split (at the middle, called the centromere) • Chromosome pairs (sisters) separate and move to opposite ends of the cell • spindle fibres help this process

  18. Phase 4: Telophase • Chromosomes reach opposite ends of the cell • Membranes begin to form around each set of daughter cells’ nuclear material • Nucleolus begins to appear in each cell • Chromosomes become less coiled and harder to see (return to chromatin form) • Spindle fibres disappear • Cytokinesis begins

  19. Cytokinesis • Cytoplasm & cell organelles divide into two equal parts • Two daughter cells are formed

  20. Sooo… let’s recap Mnemonic to remember the stages of cell division: IPMATC (ip-MAT-see)

  21. Sexual vs. Asexual Reproduction:What’s the diff, anyway? • Asexual reproduction involves one organism • the parent cell makes 2 daughter cells that are identical to the parent • aka cloning • body cells & single-celled organisms reproduce this way • Sexual reproduction involves two organisms • two parent cells (sperm & egg) create 1 daughter cell • the offspring receives half of its genes from each parent • daughter cell is 50% mom, 50% dad

  22. Asexual Reproduction Cell division is an example of asexual reproduction

  23. Sexual Reproduction haploid = 23 chromosomes diploid = 2 x 23 chromosomes meiosis = cell division of sex cells

  24. Mitosis & cytokinesis are only a fraction of the cell cycle!

  25. Quiz time! • i. Identify which number represents the following stages of cell division: • interphase • prophase • metaphase • anaphase • telophase • cytokinesis • ii. Identify the following structures: • parent cell • daughter cells • nucleus (3x) • sister chromatids (3x) • spindle fibres (4x) • centrosomes (at least 3x)

  26. Can’t get enough??? • Check out http://www.biologycorner.com/bio1/cellcycle.html for more cool visuals on mitosis!

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