TRANSPORT ACROSS MEMBRANES

THE WAY CELLS REGULATE THEIR CONTENTS

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)

Passive Transport

DiffusionBulk FlowElectrodiffusionCurrent FlowOsmosisFacilitated Diffusion

Diffusion

Diffusion occurs when concentration in one region is greater than in another

The end result is an even distribution called equilibrium

Before:

After:

Diffusion across a permeable membrane

Diffusion occurs when concentration in one region is greater than in another

The end result is an even distribution called equilibrium

Before:

After:

Impermeable membrane

Diffusion can not occur

Before:

After:

Bulk Flow

Analogous to the flow of water through a pipe

Through pores in membranesThrough blood vesselsThrough other tubular structures

Current Flow

+ -

POSITIVE REGION NEGATIVE REGION

CATIONS AND ANIONS MOVE IN OPPOSITE DIRECTIONSCARRYING ELECTRICAL CURRENT

CURRENT = FLOW OF CATIONS - FLOW OF ANIONS

Osmosis

SOLUTENO

SOLUTE SOLUTENO

SOLUTE

Before: After:

Water moves across a semi-permeable membrane to the side where the solute is most concentrated

Facilitated Diffusion1. Molecule binds to

carrier2. Carrier changes

conformation3. Molecule released

on other side4. Purely passive

process- stops when concentrations are equal

ACTIVE TRANSPORT REQUIRES AN INPUT OF ENERGY

USUALLY IN THE FORM OF ATPATPase IS INVOLVEDSOME ASYMMETRY IS NECESSARYCAN PUMP UPHILL

ACTIVE TRANSPORT

ADP

ATP