8.1: CELL TRANSPORT across the cell membrane

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8.1 CELL TRANSPORT (across the cell membrane!)
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Selectively permeable

• property of biological membranes which allows
  some substances to pass more easily than others

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Transport proteins

• membrane proteins that transport SPECIFIC
  molecules or ions across biological membranes

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GLUCOSE
Binding
Transport
Recovery
Dissociation
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Movement across the cell membrane can be

• 1) PASSIVE
• cell does not have to spend energy
• substance moves from where it is MORE
  concentrated to where it is LESS concentrated.
• 2) ACTIVE
• ? cell spends energy to move a substance from
  where it is LESS concentrated to where it is MORE
  concentrated (UPHILL)

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Passive Transport DIFFUSION

• movement of a substance from where it is conc. to
  where it is less conc. (down a concentration
  gradient)

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Passive Transport OSMOSIS

• diffusion of WATER
• across a selectively
• permeable membrane
• water moves DOWN its
• concentration gradient

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INSIDE THE CELL
OUTSIDE THE CELL
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• the direction of water movement water can be
  described/predicted based on if the cells
  environment is
• ISOTONIC equal solute concentration compared to
  inside a cell
• HYPERTONIC greater solute concentration than
  inside a cell
• HYPOTONIC lower solute concentration compared to
  inside a cell
• WATER MOVES FROM HYPO TO HYPERTONIC!!!

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In animal cells

• in a HYPERTONIC environment,
• water exits the cell
• cells shrivel and usually die
• in a HYPOTONIC environment,
• water moves into cell,
• causing it to swell and
• possibly burst

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In cells with cell walls (i.e. plant cells)

• in a HYPERTONIC environment, water exits the
  cell cells shrivel and usually die
• in a HYPOTONIC environment, water moves into
  cell, causing it to swell cells become more
  TURGID.

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Passive Transport FACILITATED DIFFUSION

• diffusion of solutes across a membrane, with the
  help of transport proteins
• (passive transport because it is movement down a
  concentration gradient cell does not need to
  spend any energy)

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ACTIVE TRANSPORT energy-requiring process
molecules are moved across the cell membrane
AGAINST their concentration gradient (uphill)
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Proton Pump!
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ACTIVE TRANSPORT ENDOCYTOSIS EXOCYTOSIS

• transport of large molecules (e.g. proteins and
  polysaccharides) into or out of the cell

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exporting large molecules by vesicles fusing w /
the cell membrane vesicle buds from ER or Golgi
and migrates to cell membrane used by cells to
export products (e.g. cells in pancreas secreting
insulin)
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2 types of Endocytosis

• 1) Phagocytosis solid particles (cell eating)
• 2) Pinocytosis fluid droplets (cell drinking)

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Phagocytosis
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Pinocytosis
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What are the 3 types of passive transport across
a membrane?

• Diffusion, osmosis, and exocytosis
• Exocytosis, endocytosis, and phagocytosis
• Diffusion, facilitated diffusion, and osmosis
• Diffusion, osmosis, and endocytosis