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TRANSPORT ACROSS CELL MEMBRANE-II
بسم الله الرحمن الرحيم
Prepared byDr.Mohammed Sharique Ahmed Quadri
Assistant prof. PhysiologyAl Maarefa College
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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
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Active Transport
Active transport• Moves a substance against its concentration
gradient
• Requires a carrier molecule
• Requires energy
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Types of Active Transport
• Active Transport1. 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
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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.
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Primary Active Transport
Active Transport
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Na+/K+ Pump
• Carrier protein has enzymes activity ( ATPase)
• Extrudes 3 Na+ and transports 2 K+ inward against concentration gradient.
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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.
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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
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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.
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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+.
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cotransport
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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
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Vesicular transport across membrane
• Exocytose
• Endocytosis
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Types of Active Transport
• Endocytosis: taking bulky material into a cell • Uses energy• Cell membrane in-folds
around food particle• “cell eating”• forms food vacuole &
digests food• This is how white blood
cells eat bacteria!
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Types of Active Transport
3. Exocytosis: Forces material out of cell in bulk• membrane surrounding the
material fuses with cell membrane
• Cell changes shape – requires energy
• EX: Hormones or wastes released from cell
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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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