Life Cycle

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Life Cycle of a Cell
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Cell Size
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• Why not just one large cell?
• Difficult to get nutrients in and waste out

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Phases of The Cell Cycle
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G1,S, and G2 are known together as Interphase.
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Regular Cells
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Interphase

• Somatic cell cycle 
• G1 phase- Gap phase, cell undergoes growth.
• S phase- DNA synthesis
• G2 phase- Gap phase. Preparation for Mitosis.
  Organelles are produced.
• M phase- Cell division (Mitosis and cytokinesis)

Sex cells are called gametes
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G1 Phase
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• Cell grows

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S Phase
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• Chromosomes Condense
• Chromosomes are inherited genetic information
• Chromosomes are made up of DNA
• Can only be seen when cells are dividing

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S Phase
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• Chromosomes replicate-or copy is made
• The two copies are
• -attached together at a point called a
  centromere.
• -are called sister chromatid.

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G2 Phase
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• Organelles must be replicated (copied)

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M Phase
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• Two parts
• Nuclear division
• Mitosis
• Cytoplasmic Division
• Cytokinesis

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Mitosis
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• Nuclear Division.
• Nucleus divides into two new nuclei Mitosis keeps
  the number of chromosomes constant from one cell
  generation to the next.
• In eukaryotes, it is the main process by which
  growth and tissue repair is accomplished.
• Mitosis is also the main process by which
  single-celled and many multi-celled eukaryotes
  reproduce asexually.

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4 Steps of Mitosis (PMAT)
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•  Prophase Chromosomes condense and attach to the
  spindle fibers at their centromere.
• Nuclear
• Membrane
• breaks down.

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Steps of Mitosis (PMAT)
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•  Prophase Centrioles move to opposite sides of
  the cell and organize the spindle fibers

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Metaphase Chromosomes attach to spindle
fibersand line up in the middle of the cell
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Anaphase Chromosomes separate-Move to opposite
sides of the cell
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Telophase
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There are now TWO nuclei in one cell!

• Nuclear Envelope reforms

And they contain the SAME genetic
informationSAME NUMBER OF CHROMOSOMES
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Cytokinesis
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• Cytoplasmic division
• Each cell gets half of the organelles.
• After mitosis cell pinches in half to form two
  new cells.

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Cytokinesis
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• Animal cells pinch.
• Cytokinesis in plant cells is different from that
  in animal cells.

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In plant cells a cell plate forms from the inside
out.
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Results of Mitosis and Cytokinesis
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• Two new cells.
• The new cells- called daughter cells- have the
  same number of chromosomes as the mother cell.
• This occurs in all somatic cells in your body.
• You have 46 chromosomes in all of your somatic
  cells-23 pair!

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Mitosis in Onion
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• Cells
• during
• Mitosis

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Concept Map
Cell Cycle
includes
is divided into
is divided into
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Reproduction of Sex Cells
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• Sex cells- Sperm and egg
• Process is called Meiosis
• Similar to Mitosis

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Meiosis
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• Cell divides twice
• First division is like mitosis and then the cell
  divides again to create 4 haploid cells.

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MEIOSISCHROMOSOME REDUCTION DIVISION
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Meiosis
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• Meiosis is also know as chromosome reduction
  division.
• Start with 46 and ends up with 23.
• Why?
• Fertilization creates the diploid condition again

Haploid
Diploid
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• Sperm formation- 4 haploid sperm cells are
  formed.
• Egg formation-most of the cytoplasm is used in
  one cell and the other three disintegrate. One
  haploid egg cell is formed.

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• Meiosis
• Video Clip

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Crossing Over
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• Sometime during meiosis the chromosomes can
  exchange information
• This is called Crossing Over
• Major source of genetic diversity in the species

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Prokaryotic Cells
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• Binary fission
• Occurs in Prokaryotic Cells
• DNA is copied and then the cell splits in half.

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Regulation of the Cell Cycle
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• How do cells know when to divide? When to stop
  dividing?
• Cyclins-proteins that regulate the cell cycle.

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Cancer
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• Unregulated cell growth.
• Can form masses of cells called tumors.