Cell Transport

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Cell Transport

• Moving things into and out of the cell through
  the cell membrane to maintain balance
  (homeostasis)
• Passive
• Doesnt take any energy from the cell
• Just happens (kinetic energy of molecules)
• Active
• Uses the cells energy, from mitochondria
• ATP (Adenosine TriPhosphate)

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Cell Memebrane

• Phospholipid Bilayer
• 2 layers, back to back, of molecules of fat
  called phospholipids
• Fluid Mosaic
• Other molecules, too, like proteins, but they
  dont just sit there, they move around
• Selectively permeable
• Not just anything can pass through

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Cell membrane
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Diffusion

• Molecules simply move from an area of higher
  concentration to lower (with concentration
  gradient)
• Because of the molecules kinetic energy
  (passive)
• Will stop when reach equilibrium (equal
  concentration)
• Molecules still move, but for each one that
  moves in to the cell, one moves out (no net
  movement)

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Diffusion across cell membrane

• Happens only for very small particles (salt,
  etc.)
• Move between phospholipid molecules of the
  bilayer
• Or for molecules that are nonpolar
  (hydrophobic) and dissolve into the space
  between the two layers of the cell membrane, but
  not in water

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Facilitated diffusion

• For molecules that are too big to get in (e.g.
  sugar), or have charges (ions)
• Proteins in the cell membrane will chemically
  bind to the molecule. (specificonly 1 molecule
  per proteinlike a lock and key)
• The protein will then change shape and the
  molecule will move in or out of the cell.
• Takes no energy (passive)

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Facilitated diffusion

• Note each protein is specific for one molecule,
  but there are many different proteins in each
  cell membrane

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Osmosis

• Special kind of diffusion (passive)
• Only for water across the membrane
• Water can move against its concentration
  gradient, that is water can move from low water
  to high water concentration
• Water moves to water down whatever is most
  concentrated.

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Osmosis

• If the cell has more stuff dissolved outside
  than inside, it is in a hypertonic environment
• It will try to water down the environment to
  make it less harsh
• Water leaves the cell, the cell shrinks
  (plasmolysis)
• http//www.youtube.com/watch?vgWkcFU-hHUkfeature
  related

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Osmosis

• If the cell has more stuff dissolved inside
  than outside, it is in a hypotonic environment
• It will try to water down the inside to make
  it less harsh
• Water enters the cell, the cell grows
• If it gets too big, it explodes (cytolysis)
• http//vimeo.com/2726364

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Osmosis

• If the cell has equal amounts of stuff
  dissolved inside and out, it is in an isotonic
  environment
• Water molecules will move both in and out of the
  cell equally, so there is no net movement of
  water
• Notes water still moves in and out in
  hypertonic and hypotonic solutions, but the net
  movement is in one direction

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Equilibrium

• Passive transport will continue until equal
  concentrations are reached in and out of the
  cell (equilibrium).
• Molecules still move back and forth across the
  membrane, but do so at equal rates
• No net (total) movement of molecules, though

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Active Transport

• Sometimes cell wants higher or lower
  concentrations (not equilibrium)
• Have to use the cells energy (ATP adenosine
  triphosphate)
• Moves against concentration, i.e. from low to
  high concentration
• Moves large molecules or large amounts of
  molecules

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Protein Pumps

• Energy changes shape of the protein to move
  things in/out of the cell
• Is specificeach protein can only chemically
  bind with one molecule, but there are many
  different proteins in the cell membrane (like a
  lock and key)
• Na K pump

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Protein pumps

• 3 sodiums are taken out of the cell and 2
  potassiums brought in using ATP.

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Transport by vesicle

• Moves large molecules or large quantities of
  something into and out of the cell
• Into the cell is called endocytosis
• Pinocytosis water/liquid moves
• Phagocytosis solids move
• Out of the cell is called exocytosis (e.g.
  products from Golgi Apparatus)

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Endocytosis

• Note part of cell membrane makes the vesicle and
  is now inside the cell!
• http//www.youtube.com/watch?vW6rnhiMxtKU

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Exocytosis

• Note the vesicle fuses with the cell membrane
  and is now part of it!
• http//www.youtube.com/watch?vU9pvm_4-bHg

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ATP

• Adenosine Triphosphate
• ATP

• Adenosine Diphosphate
• ADP P energy