TRANSPORT ACROSS MEMBRANES

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TRANSPORT ACROSS MEMBRANES

• THE WAY CELLS REGULATE THEIR CONTENTS

2
TWO MAJOR TYPES OF TRANSPORT

• PASSIVE Only from high concentration to low
• ACTIVE Can actually pump up a gradient using
  energy from some other source such as ATP
  (Primary) or another gradient (Secondary)

3
Passive Transport

• Diffusion
• Bulk Flow
• Electrodiffusion
• Current Flow
• Osmosis
• Facilitated Diffusion

4
Diffusion
Before

• Diffusion occurs when concentration in one region
  is greater than in another
• The end result is an even distribution called
  equilibrium

After
5
Diffusion across a permeable membrane
Before

• Diffusion occurs when concentration in one region
  is greater than in another
• The end result is an even distribution called
  equilibrium

After
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Impermeable membrane
Before

• Diffusion can not occur

After
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Bulk Flow

• Analogous to the flow of water through a pipe
• Through pores in membranes
• Through blood vessels
• Through other tubular structures

8
Current Flow
POSITIVE REGION
NEGATIVE REGION

CATIONS AND ANIONS MOVE IN OPPOSITE
DIRECTIONS CARRYING ELECTRICAL CURRENT CURRENT
FLOW OF CATIONS - FLOW OF ANIONS
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Osmosis
Water moves across a semi-permeable membrane to
the side where the solute is most concentrated

After
Before
SOLUTE
NO SOLUTE
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Facilitated Diffusion

• 1. Molecule binds to carrier
• 2. Carrier changes conformation
• 3. Molecule released on other side
• 4. Purely passive process- stops when
  concentrations are equal

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ACTIVE TRANSPORT REQUIRES AN INPUT OF ENERGY

• USUALLY IN THE FORM OF ATP
• ATPase IS INVOLVED
• SOME ASYMMETRY IS NECESSARY
• CAN PUMP UPHILL

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ACTIVE TRANSPORT
ADP
ATP