MEMBRANE TRANSPORT
CELL PHYSIOLOGY:
MEMBRANE TRANSPORT
• Membrane transport—movement of
substances into and out of the cell
• Two basic methods of transport
• Passive transport
• No energy is required
• Active transport
• Cell must provide metabolic energy (ATP)
PASSIVE TRANSPORT
• Diffusion
• Particles distribute themselves evenly within a solution
• Movement from high concentration to low concentration,
PASSIVE TRANSPORT
• Diffusion
1. They are small enough to pas through pores
2. They can dissolve in fatty portion of membrane
3. They are assisted by membrane carrier
PASSIVE TRANSPORT
• Simple Diffusion: unassisted
• lipid-soluble materials / small enough to pass through
membrane pores
PASSIVE TRANSPORT
PASSIVE TRANSPORT
PASSIVE TRANSPORT
ACTIVE TRANSPORT
Extracellular fluid
Na+
K+
Na+
P
Na+
P
Na+
Na+
K+
K+
Na+
P
K+
ATP
ADP
Binding of cytoplasmic Na+
to the pump protein
stimulates phosphorylation
by ATP, which causes the
pump protein to change its
shape.
The shape change expels
Na+ to the outside.
Extracellular K+ binds,
causing release of the
phosphate group.
Loss of phosphate restores
the original conformation of
the pump protein. K+ is
released to the cytoplasm and
Na+ sites are ready to bind Na+
again; the cycle repeats.
Cytoplasm
ACTIVE TRANSPORT: EXOCYTOSIS
ACTIVE TRANSPORT: EXOCYTOSIS
ACTIVE TRANSPORT: ENDOCYTOSIS
Extracellular
fluid
Cytoplasm
Pit
Extracellular
fluid
Plasma
membrane
Recycling of membrane
and receptors (if present)
to plasma membrane
Ingested
substance
Transport to plasma
membrane and
exocytosis of
vesicle contents
Vesicle
Lysosome
Detachment
of vesicle
Plasma
membrane
(a)
Vesicle containing
ingested material
Vesicle fusing
with lysosome
for digestion
Release of
contents to
cytoplasm
ACTIVE TRANSPORT: ENDOCYTOSIS
Phagocytosis
Receptor-mediated
endocytosis
CELL PHYSIOLOGY:
MEMBRANE TRANSPORT
• https://www.youtube.com/watch?v=dPKvHrD1eS4
• https://www.youtube.com/watch?v=YfoiHrv57b0