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Limits to Cell Growth: Why Cells Do Not Grow Larger

This article explores the limits to cell growth and the reasons why cells do not grow larger to increase the size of an organism. Factors such as DNA limitations and the movement of materials are discussed, along with the solution of cell division to increase organism size. Mitosis, the process of making new cells and DNA, is also explained.

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Limits to Cell Growth: Why Cells Do Not Grow Larger

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  1. Limits to Cell Growth ? Do cells grow larger to increase the size of the organism? NO!! Why? 1) DNA - cell parts rely on DNA for instructions - increase in size = more parts needing info * DNA has a limit on ability to send out instructions

  2. 2) Movement of Materials - increase in size = larger volume (inner space) less surface area (cell membrane) Therefore: - materials get crowded moving in/out of cell Example: 1cm x 1cm cell3cm x 3cm cell Surface Area = 1cm x 1cm x 6 sides 3cm x 3cm x 6 = 6 cm2 = 54 cm2 Volume = 1cm x 1cm x 1cm 3cm x 3cm x 3cm = 1cm3 = 27 cm3 Ratio = 6 to 12 to 1

  3. Solution - Cell division increases the number of cells which increases the organism’s size.

  4. Biology is the only subject in which multiplication is the same thing as division…

  5. MITOSIS:Making New CellsMaking New DNA

  6. Where it all began… We all start as a cell smaller than a period at the end of a sentence…

  7. And now look what can happen… How did you get from there to here?

  8. Getting from there to here… • Going from egg to baby…. the original fertilized egg has to divide… and divide… and divide… and divide…

  9. Why do cells divide… • One-celled organisms • for reproduction • asexual reproduction(clones) • Multi-celled organisms • for growth & development • fromfertilized eggto adult • for repair & replacement • replace cells that die from normal wear & tear or from injury amoeba starfish

  10. Dividing cells… • What has to be copied • DNA • organelles • cell membrane • lots of othermolecules • enzymes plant cell animal cell

  11. Copying DNA • A dividing cell duplicates its DNA • creates 2 copies of all DNA • separates the 2 copies to opposite ends of the cell • splits into 2 daughter cells • But the DNA starts loosely wound in the nucleus • If you tried to divide it like that, it could tangle & break DNA cell nucleus

  12. Coil DNA into compact chromosomes Copying DNA Copying & packaging DNA • When cell is ready to divide… • copy DNA first, then… • chromosomes COIL UPlike thread on a spool… • now can move DNA around cell without having it tangle & break

  13. Organizing & packaging DNA DNA cell DNA has been “wound up” nucleus DNA in chromosomes ineveryday “working” cell cell nucleus 4 chromosomesin this organism DNA in chromosomes in cell getting ready to divide

  14. chromosomes in cell DNA in chromosomes cell 4 single-stranded chromosomes duplicated chromosomes nucleus duplicated chromosomes cell nucleus 4 double-stranded chromosomes DNA must be duplicated…

  15. double-strandedhuman chromosomes ready for mitosis

  16. Chromosomes of Human Female 46 chromosomes 23 pairs

  17. Chromosomes of Human Male 46 chromosomes 23 pairs

  18. Cell Cycle: Life Cycle of Cells • Stage 1: cell copies DNA - period of growth & division of a cell DNA Interphase 3 Stages G1 phase- cell growth S phase- DNA replication G2 phase- new organelles cell nucleus

  19. Cell Cycle

  20. Mitosis: Dividing DNA & cells • Stage 2: DNA winds up into chromosomes • DNA is wound up into chromosomes to keep it organized duplicated chromosomes (prophase) cell nucleus

  21. Mitosis: Dividing DNA & cells • Stage 3: Chromosomes line up • chromosomes line up in middle • attached to protein “cables” that will help them move metaphase duplicated chromosomes lined up in middle of cell

  22. Mitosis: Dividing DNA & cells • Stage 4: Chromosomes separate • chromosomes split, separating pairs • start moving to opposite ends anaphase chromosomes split & move to opposite ends

  23. Mitosis: Dividing DNA & cells • Stage 5: Cell starts to divide • cells start to divide • nucleus forms again Telophase - Animals - cell pinches in - Plants- cell plate forms

  24. Mitosis: Dividing DNA & cells • Stage 6: DNA unwinds again • cells separate • now they can do their every day jobs cytokinesis

  25. New “daughter” cells • Get 2 exact copies of original cells • same DNA • “clones”

  26. Cell division in Animals

  27. Mitosis in whitefish embryo

  28. Mitosis in plant cell

  29. onion root tip

  30. I.P.M.A.T.C. Overview of mitosis interphase prophase PleaseMake Another Two Cells cytokinesis metaphase anaphase telophase

  31. Any Questions?? Any Questions??

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