TRANSPORT ACROSS CELL MEMBRANE-II
Prepared by
Dr.Mohammed Sharique Ahmed Quadri
Assistant prof. Physiology
Al Maarefa College
Objectives
• Describe how energy from ATP hydrolysis is used to
transport ions against their electrochemical
concentration differences
• Explain how energy from the Na+ and K+
electrochemical gradients across the plasma
membrane can be used to drive the net “uphill”
(against a gradient) movement of other solutes.
• Describe the characteristics of carrier-mediated
transport, and distinguish between simple diffusion,
facilitated diffusion, and active transport
• Describe the process of vesicular transport
Active Transport
Active transport
• Moves a substance against its concentration
gradient
• Requires a carrier molecule
• Requires energy
Types of Active Transport
•
Active Transport
1. Protein Pumps
•
•
Primary active transport
– Requires direct use of ATP
Secondary active transport
– Driven by an ion concentration gradient
established by a primary active transport system
2. Vesicular transport
•
•
Endocytosis
Exocytosis
Primary Active Transport
• Movement against concentration gradient
• Hydrolysis of ATP directly required for the function
of the carriers.
• Molecule or ion binds to “recognition site” on one
side of carrier protein.
• Carrier protein undergoes conformational change.
– Hinge-like motion releases transported molecules to
opposite side of membrane.
Primary Active Transport
Active Transport
Na+/K+ Pump
• Carrier protein has
enzymes activity (
ATPase)
• Extrudes 3 Na+ and
transports 2 K+ inward
against concentration
gradient.
Na+/K+ Pump
• Steep gradient created by this pump serves
following functions:
• Provides energy for “coupled transport” of
other molecules.
• Involvement in electrochemical impulses.
• Promotes osmotic flow.
Importance of Na+- K+ pump in intestinal
epithelium
• High osmotic pressure created by movement
of sodium causes water to move from
intestinal lumen to interstitial space
• Protein and glucose r transported actively by
cotransport with sodium
• Chloride passively follow the electrical
gradient created by sodium
Secondary Active Transport
• Transport of two or more solutes are Coupled
.
• Energy needed for “uphill” movement
obtained from “downhill” transport of Na+.
• Hydrolysis of ATP by Na+/K+ pump required
indirectly to maintain [Na+] gradient.
Secondary Active Transport
• Cotransport (symport):
– Molecule or ion moving in the same direction as
Na+.
• Countertransport (antiport):
– Molecule or ion moving in the opposite direction
of Na+.
cotransport
Counter transport
– Molecule or ion moving
in the opposite direction
– E.g. Na+-Ca2+ exchange
– As with cotransport it
also uses Na gradient
established by the Na+K+ ATPase as an energy
source
– Na+ moves downhill &
Ca2+ moves uphill
Vesicular transport across membrane
• Exocytose
• Endocytosis
Types of Active Transport
Types of Active Transport
Vesicle-mediated transport
Vesicles and vacuoles that fuse with the cell membrane may be utilized to release or
transport chemicals out of the cell or to allow them to enter a cell. Exocytosis is the
term applied when transport is out of the cell.
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References
• Human physiology by Lauralee Sherwood, fifth
edition
• Text book physiology by Guyton &Hall,11th
edition
• Text book of physiology by Linda .s
contanzo,third edition
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