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Why Would a Cell Divide?As cells absorb nutrients and get larger, the volume
of the cell increases faster than the surface area
This means that a cell can no longer absorb nutrients and get rid of wastes fast enough to support its demands (volume)
So what’s a cell to do?
Solution: divide in 2!
Surface area for exchange not great enough to support cell’s needs
Three reasons why cells reproduce by asexual reproduction:
1. Growth 2. Repair 3. Replacement
Different cells divide at different rates:Most mammalian cells = 12-24 hoursSome bacterial cells = 20-30 minutes
Cell Type Typical Lifespan
Intestinal Lining
?
Skin Cell ?
Red Blood Cell ?
Liver Cell ?
Intestine –Muscle and other tissue
?
Cell Type Typical Lifespan
Intestinal Lining
4-5 Days
Skin Cell 2 Weeks
Red Blood Cell 4 Months
Liver Cell 300 – 500 Days
Intestine –Muscle and other tissue
16 years
Interphase occurs before mitosis begins
• Chromosomes are copied (# doubles)
• Cell growth and organelles are doubled
• Preparing for mitosis
Prophase 1st step in Mitosis
• Mitosis begins (cell begins to divide)
• Centrioles appear and begin to move to opposite end of the cell.
• Spindle fibers form between the poles.
Metaphase 2nd step in Mitosis
• Chromatids (or pairs of chromosomes) attach to the spindle fibers and line in middle.
Anaphase 3rd step in Mitosis
• Chromatids (or pairs of chromosomes) separate and begin to move to opposite ends of the cell.
Telophase 4th step in Mitosis
• Two new nuclei form. • Chromosomes appear
as chromatin (threads rather than rods).
• Mitosis ends.
Cytokinesisoccurs after mitosis
• Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes.
Regulatory Proteins Internal- Protein that regulates the
timing of the cell cycle inside the cell (ex: cyclin).
External- Protein that can cause the cell cycle to speed up or slow down (ex: growth factors, contact inhibition).
*Apoptosis*-programmed cell death.
Uncontrolled growth of cells
Cancer – body loses ability to control growth.› *Damaged P53 gene*› Causes: tobacco, radiation exposure, viral
infection, etc. Tumors- mass of cells
› Can damage surrounding area› Can break off and spread throughout body
Stem Cells Unspecialized
cells process by which
cells become specialized is known as differentiation.