The cell cycle and cell division

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The cell cycle and cell division

• Why is it called the cell cycle?

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Before the cell can divide, DNA must be copied

• Semiconservative- one old strand, one new strand
• Increases accuracy

After replication
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The life cycle of a cell
G1 can last for a few minutes or decades
Genes control cell division Loss of control
cancer
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How do cells die?
programmed cell death
injury
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The stages of mitosis
What do you get? Two identical cells
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Why do cells divide?

• So we can get bigger (cells dont get bigger, we
  accumulate more cells)
• To repair damage
• Reproduction in some organisms
• How many times can cells divide?
• Embryonic stem cells- unlimited
• Differentiated cells- it depends
• Lack of regulation can lead to cancer
• Can we control regulation?

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Sexual reproduction and meiosis

• Sperm and egg deliver two halves of a genome
• Some terminology
• Gametes sex cells
• Diploid a cell with two copies of each
  chromosome
• Diploid number 2n
• Haploid a cell with one copy of each chromosome
• Haploid number n
• Meiosis cell division process by which gametes
  are formed

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Karyotype one chromosome comes form each parent
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Meiosis Two rounds of cell division In humans,
each daughter cell has 23 chromosomes
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Many possible combinations of chromosomes are
possible
Random assortment Crossing over
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Not identical in human males and females
Feature Males Females
When does meiosis begin? How long does each step take? Begins at puberty Each step takes about the same time (64 days total) Begins during embryonic development May remain in meiosis I for decades (may never complete meiosis)
How is meiosis completed? Spermatocytes will complete meiosis Meiosis II happens only with fertilization
How many gametes are formed? 4 spermatids are formed One ovum is formed
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Summary

• The cell cycle is its life history. Not all cells
  in the body have the same history.
• Cells divide by mitosis to form exact copies of
  themselves
• Meiosis forms gametes, and is the basis of sexual
  reproduction