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Dr Fatahiya Kashif The Cell
Transport across the cell membrane
Dr Fatahiya Kashif The Cell
Objectives
• To appreciate how solutes and other materials move across the cell membrane
• Become familiar with different types of transport proteins
• An understanding of the importance of membrane transport to living cells
Dr Fatahiya Kashif The Cell
TYPES OF TRANSPORT
Passive transport Active transport
Dr Fatahiya Kashif The Cell
Passive transport
• Simple diffusion • Facilitated diffusion
Dr Fatahiya Kashif The Cell
Simple diffusion
• Downhill
Dr Fatahiya Kashif The Cell
SIMPLE DIFFUSION
Dr Fatahiya Kashif The Cell
Simple diffusion
• Fick law
J = P X A(C1-C2)
• J = rate of diffusion mmol/s• P = permeability coefficient • A = membrane surface area cm²• C = concentration of the substance mmol/L
Dr Fatahiya Kashif The Cell
Factors affecting diffusion rate
• Permeability coefficient – Diffusion coefficient• Temperature• Molecular radius • Viscosity
– Partition coefficient• Solubility in oil vs water
– Thickness of the membrane/distance • Lungs • Placenta
Dr Fatahiya Kashif The Cell
Factors affecting diffusion rate
• Surface area– Lungs – Intestinal lining– Capillaries
Dr Fatahiya Kashif The Cell
Factors affecting diffusion rate
• Concentration gradient – Effect on the rate?– What is equilibrium state? – How to achieve a constant rate of diffusion?– Gas exchange in lungs
Dr Fatahiya Kashif The Cell
FACILITATED DIFFUSION
Dr Fatahiya Kashif The Cell
Facilitated diffusion
• Carrier proteins – Glucose transporters• GLUT family • GLUT 1 all cells• GLUT 4 insulin dependent
– Muscle – Adipose
Dr Fatahiya Kashif The Cell
Simple diffusion vs carrier mediated/facilitated diffusion
Carrier mediated
Simple diffusion
Tran
spor
t rat
e
Concentration
Transport maximum (Tm)
Dr Fatahiya Kashif The Cell
Transport of charged ions
• What happens to charged molecules?– Permeability of the membrane• Carriers
– Electrical gradient– Electrochemical equilibrium– How to maintain an electrochemical gradient
Dr Fatahiya Kashif The Cell
ACTIVE TRANSPORT
Dr Fatahiya Kashif The Cell
Active transport
• Primary active transport • Secondary active transport
Dr Fatahiya Kashif The Cell
PRIMARY ACTIVE TRANSPORT Uphill
Dr Fatahiya Kashif The Cell
Pumps
• ATPases• Na⁺-K⁺ pump• Ca⁺⁺ ATPase• H⁺-K⁺ ATPase
Dr Fatahiya Kashif The Cell
Na⁺-K⁺ ATPase
• All cells • Electrical signaling in neurons• Secondary active transport
Dr Fatahiya Kashif The Cell
SODIUM
POTASSIUM
Dr Fatahiya Kashif The Cell
ATPADP+PiMg++
SODIUM
POTASSIUM
Dr Fatahiya Kashif The Cell
SODIUM
POTASSIUM
Dr Fatahiya Kashif The Cell
SODIUM
POTASSIUM
Dr Fatahiya Kashif The Cell
Ca⁺⁺ ATPase
• Intracellular Ca⁺⁺ concentration• Sarcoplasmic reticulum
Dr Fatahiya Kashif The Cell
Primary active transport of calcium
Dr Fatahiya Kashif The Cell
CALCIUM
Primary active transport of Calcium
Dr Fatahiya Kashif The Cell
CALCIUM
Primary active transport of Calcium
ATP
Dr Fatahiya Kashif The Cell
CALCIUM
Primary active transport of Calcium
ADP+Pi
Dr Fatahiya Kashif The Cell
H⁺-K⁺ ATPase
• Stomach • Kidney
Dr Fatahiya Kashif The Cell
H2CO3
HCO3-Cl-
Primary active transport of Hydrogen ions
Gastric parietal cellPlasma Lumen
ATPaseH+
Dr Fatahiya Kashif The Cell
H2CO3
H+
HCO3- Cl-
Primary active transport of Hydrogen ions
Gastric parietal cellPlasma Lumen
ATPase
Dr Fatahiya Kashif The Cell
H2CO3
H+HCO3- Cl-HCl
Primary active transport of Hydrogen ions
Gastric parietal cellPlasma Lumen
Dr Fatahiya Kashif The Cell
SECONDARY ACTIVE TRANSPORTUphill
Dr Fatahiya Kashif The Cell
Secondary active transport
• Cotransport/symport– Na⁺-glucose– Na⁺-aminoacid– Na⁺-Cl⁻ cotransporter– K⁺- Cl⁻ cotransporter– Na⁺- K⁺-2 Cl⁻ cotransporter
• Countertransport – Na⁺- Ca⁺⁺ exchanger– Na⁺- H⁺ exchanger– Cl⁻-HCO3⁻ exchanger
Dr Fatahiya Kashif The Cell
Glucose
Sodium
Co-transport of glucose with sodium ions
Dr Fatahiya Kashif The Cell
Glucose
Sodium
Co-transport of glucose with sodium ions
Dr Fatahiya Kashif The CellDr Fatahiya Kashif
Cotransport of ions
300
600
1200
Med
ull
aC
ort
ex
K+Na+2Cl-
Dr Fatahiya Kashif The Cell
Red blood cells
H2OCO2
Dr Fatahiya Kashif The Cell
Red blood cells
H2CO3
HCO3- H+
Dr Fatahiya Kashif The Cell
Red blood cells
H2CO3
H+HCO3-Cl-
Dr Fatahiya Kashif The Cell
RENAL TUBULAR CELL
TUBULAR LUMEN
INTERSTITIAL FLUID
BLOOD
3Na+
2K+
H2CO3
HCO3- H+
Renal regulation
Dr Fatahiya Kashif The Cell
RENAL TUBULAR CELL
TUBULAR LUMEN
INTERSTITIAL FLUID
BLOOD
H2CO3
HCO3- H+
Na+
Dr Fatahiya Kashif The Cell
Calcium
Sodium
Sodium counter-transport of Calcium ions
Dr Fatahiya Kashif The Cell
Calcium
Sodium
Sodium counter-transport of Calcium ions
Dr Fatahiya Kashif The Cell
Calcium
Sodium
Sodium counter-transport of Calcium ions
Dr Fatahiya Kashif The Cell
GLUT 5
GLUT 2
3Na+
2K+
O
Na+
O
Na+
Na+
Na+
Na+
Na+
O
SGLT-1
O
ONa+
O
Dr Fatahiya Kashif The Cell
GLUT 5
GLUT 2
O
Na+
O
Na+
Na+
Na+
Na+
Na+
O
SGLT-1O
Na+
O
GLUT 2O
Dr Fatahiya Kashif The Cell
Na+3Na+
2K+
Dr Fatahiya Kashif The Cell
Na+
Dr Fatahiya Kashif The Cell
Na+
Dr Fatahiya Kashif The Cell
Na+
Dr Fatahiya Kashif The Cell
Na+
Dr Fatahiya Kashif The Cell
Na+
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