Cell%20Cycle

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Cell Cycle
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• Cells are the basic unit of life.
• Just like you and me, as they get older they grow
  bigger. This triggers the cell to divide.
• First, lets talk about the stages of the cell
  cycle

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G1 Phase

• Or the Growth 1 Phase is the first event in the
  life cycle of a cell.

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G1 Phase

• During this phase
• the cell is metabolically active with chemical
  reactions mostly in the cytoplasm
• Cellular respiration (makes ATP)
• Produces protein
• At the end organelles are duplicated

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S Phase

• Or the Synthesis phase.
• Synthesisto put parts together to equal a whole.
• During this phase
• DNA is replicated in the nucleus

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G2 Phase

• Or Growth 2 Phase is a second period of growth
  after the DNA has been replicated.
• (SO the cell has TWICE the amount of genetic
  material it needs)
• During this phase
• Cell resumes making proteins and other molecules

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Interphase

• Interphase G1,S,G2
• Cells spend most of their life in interphase
• During Interphase
• The cell appears normal
• Nucleus is visible
• DNA is loosely organized (bowl of spaghetti)
• This is called Chromatin

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M phase

• Or Mitosis Phase
• During Mitosis
• The nucleus divides in a series of steps to form
  two nuclei
• The nuclei, duplicated organelles and cytoplasm
  are separated in cytokinesis.

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Stages of Mitosis

• Prophase
• Metaphase
• Anaphase
• Telophase

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Prophase

• The FIRST step in Mitosis.
• During Prophase
• DNA condenses to form chromosomes
• To make a chromosome the DNA is wrapped around
  proteins called histones
• Chromosome looks like a X

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Prophase

• Chromosomes
• Each half of the X is called a chromatid.
• These chromatids are held together in the center
  of the X in a region called the centromere.

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Prophase

• Microfiliments in the cytoskeleton begin to break
  down
• In animals, Centrioles move to the opposite sides
  of the cell and form spindle fibers toward the
  center of the cell
• In plants, spindle fibers form at the opposite
  ends of the cell in regions called asters

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Prophase

• By the end of prophase, the nuclear membrane has
  been broken down and the nucleolus disappears.
• This is the longest phase of Mitosis

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Metaphase

• The second phase of mitosis
• During Metaphase
• Spindle fibers attach to the centromeres on each
  chromosome
• Chromosomes are lined up down the middle of cell.

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Anaphase

• The third phase of mitosis
• During Anaphase
• The chromatids are pulled apart at the centromere
  by spindle fibers
• Spindle fibers pull the chromatids to opposite
  sides of the cell

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Telophase

• The last phase in mitosis
• During Telophase
• Chromatids arrive at the opposite poles of the
  cell
• The nuclear membrane forms around each new set of
  chromosomes
• DNA uncoils and the nucleoli reappear

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Telophase

• Once the nuclear membrane completely forms, the
  new nuclei appear
• Each nuclei contains a complete set of
  chromosomes identical to the parent cell
• Microfiliments reform the cytoskelton and move
  the duplicated organelles to opposite sides

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Just Remember

• ProphaseMetaphaseAnaphaseTelophase

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Cytokinesis

• The division of the cytoplasm
• In animals, the cytoplasm pinches in from the top
  form the cleavage furrow
• The cleavage furrow continues to constrict
  towards the center until pinching off the two
  cells.

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Cytokinesis

• In plants, a cell plate forms in the middle of
  the cell which turns into the new cell wall.

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Controlled Cell Growth

• Cell growth and division is controlled by
  internal and external factors
• These can tell a cell to divide or to continue to
  grow
• Example Human growth hormone which tells bone
  cells to grow and divide

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Uncontrolled Cell Growth

• If uncontrolled by internal or external factors
  cells will divide continuously.
• Example Cancer
• Causes cells to form masses called tumors
• Malignancy is when a cancer cell breaks away and
  forms a new mass

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Uncontrolled Cell Growth

• Cancer cells use up nutrients and oxygen and do
  not provide any function for the organism
• The tumor can add stress to surrounding cells

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Causes of Cancer

• A carcinogen is something that causes cancer.
• Causes a mutation in the genetic material (DNA)
  which can prevent the cell from responding to
  external and internal signals.
• Examples smoking, exposure to excessive
  radiation from the Sun, pollution, and some
  viruses.