Ch'4: Cell and Their Environments

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Ch.4 Cell and Their Environments

• Bio P
• Mr. Q

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Section 4.1 Passive Transport

• What is passive transport?
• Movement of substances across the cell membrane
  without the use of the cells energy.

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What is diffusion?

• Type of passive transport.
• Movement of SUBSTANCES from an area of high
  concentration to an area of low concentration
• High ? Low
• At equilibrium concentration is equal throughout.

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What is osmosis?

• Type of diffusion and passive transport
• Movement of WATER from an area of
• Low solutes ? High solutes
• Why does water move?
• Because of THE AMOUNT OF SUBSTANCES in the
  solution.

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What type of solutions are there?

• Hypertonic high solute concentration
• Hypotonic low solute concentration
• Isotonic equal solution concentration

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What happens in cells?

• Hypertonic solution - water moves out
• Hypotonic solution - water moves in
• Isotonic solution - no water movement

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Can all substances get across the cell membrane?

• No, sometimes substances need help.
• What helps substances across the cell membrane?
• Transport proteins (a.k.a channel proteins)

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What is special about transport proteins?

• They are specific to a substance
• Ion channels allows ions to pass the membrane
• Some are always open, others need stimuli,
  stretching of cell membrane, electrical charge,
  or binding of specific molecules.

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What is facilitated diffusion?

• When a substance uses a carrier protein to cross
  the cell membrane.
• Molecule binds to the carrier protein.
• Transports molecule across the membrane.
• Molecule is released.

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Section 4.2 Active Transport

• What is active transport?
• Movement of substances across the cell membrane
  against their concentration gradient.
• Low ? High
• Energy is needed!!!! They are forced to go!!!!!!
• Energy ATP

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What is the Sodium-Potassium Pump? See fig 4-5

• A specialized carrier protein that acts as a
  pump.
• 3 sodium ions, Na out
• 2 potassium, K ions in
• Important in animal cells

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How do large molecules enter the cell?

• They use vesicles
• Examples large proteins and polysaccharides
• Vesicles into the cell endocytosis Vesicles out
  of the cell exocytosis

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Where do the vesicles come from?

• Inside the cell, usually the Golgi apparatus.

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What do membrane receptor proteins do? See fig 4-8

• Binds to signal molecules from other cells
  allowing them to communicate.
• Examples of signals hormones
• A signal molecule changes the function of a cell.

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How does it change the cell function?

• Changes in permeability
• Signal molecule causes an ion channel to open.
• Activating second messengers
• Signal molecules in the cytoplasm (Fig 4-9)

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• Starting enzyme actions
• Receptor protein may also act as an enzyme
• It may also activate other enzymes in the cell.