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Cell Cycle

This text explores the relationship between cell size and its surface area-to-volume ratio, and discusses the importance of an efficient ratio for nutrient exchange and waste removal. It also explains the limitations of cell size due to DNA coding and the process of mitosis for cell division. Illustrated with examples, this text provides insights into the role of cell surface area-to-volume ratio in cell functioning.

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Cell Cycle

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  1. Cell Cycle

  2. Surface area to volume ratio 2:1 4:1 6:1 -Which SA/V ratio would be more efficient to a cell? A large SA/V ratio…..6:1

  3. Surface area to volume ratio Each time a cell doubles in size, its surface area increases by a factor of four but its volume increases by a factor of eight. It would mean that the cell would need 8 times the normal amount of nutrients and make 8 times the normal amount of wastes.

  4. All cells are relatively the same size. Why? 1. Surface area-to-volume ratio • As a cell grows the volume increases much more rapidly than the surface area • Diffusion is slow • The larger the cell the more food and the more wastes; not efficient.

  5. Cell Size, cont. Increase size of cell Decrease rate of Diffusion Oxygen Nutrients Wastes Water

  6. Cell Size, cont. 2. DNA limits the size of a cell DNA codes for proteins, the larger the cell, the more proteins it needs. The cell can’t make instructions fast enough

  7. DNA makes up the chromosomes inside the nucleus

  8. DNA and Cell Division For the most of a cell’s lifetime, chromosomes exist as chromatin – long strands of DNA wrapped around proteins (called histones).

  9. Under an electron microscope, chromatin looks somewhat chaotic resembling a plate of spaghetti. -This is necessary for the information to be copied.

  10. Chromosome centromere Sister chromatid

  11. Onion root tip White fish blastula

  12. Chromatin vs. Chromosomes Chromatin is loosely coiled DNA Chromosomes are tightly coiled DNA -DNA is tightly coiled around proteins called histones

  13. How does chromatin condense into chromosomes? (Histones Help!)

  14. What is Mitosis? • The cell then enters mitosis. • Division of a cell’s nucleus • Chromosomes (DNA) are equally divided • 2 identical daughter cells that are formed

  15. Mitosis Step 1: Prophase • Nucleus (nuclear membrane) begins to disappear • DNA condenses from chromatin to chromosomes • Centrioles move to opposite sides of the cell • Spindle fibers start to form

  16. MitosisStep 2: Metaphase • Chromosomes line up along the equator/middle • Each chromosome is connected to a spindle fiber at its centromere • Very short phase

  17. MitosisStage 3: Anaphase • Sister chromatids are pulled to opposite poles by centrioles and spindle fibers. Chromosome Sister chromatids

  18. MitosisStep 4: Telophase • Cell membrane begins to pinch in the middle • New nuclei form around each set of chromosomes • Chromosomes unwind back into chromatin Telophase

  19. Cytokinesis: Division of the cytoplasm • Plant cell • Cell membrane does not pinch in b/c of rigid cell wall • Cell plate forms at the equator that divides the cytoplasm • Animal cell • Cell membrane pinches along equator • Forms a cleavage furrow that deepens until the cell is pinched in two

  20. Cytokinesis -Two new cells

  21. Cytokinesis Cell plate Cleavage furrow

  22. Anaphase

  23. Prophase

  24. Metaphase

  25. Interphase

  26. Cytokinesis

  27. Telophase

  28. Mitosis • In Mitosis, everything is identical. • Takes place in somatic cells (body cells, ex: lung, skin, heart, stomach, etc.)

  29. Results of Mitosis • Replace old or damaged cells. • Occurs fastest in skin cells. • Some cells like brain cells do not divide. • During early development, mitosis produces the cells needed to make tissues and organs.

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