Membrane Transport “The Ministry of Trade and Commerce for the cell”
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Membrane Transport
“The Ministry of Trade and Commerce for the cell”
Source: Molecular cell biology, Lodish, 7th Ed.
Types of TransportBased on the need for energy:
Passive
Simple Diffusion
Facilitated Diffusion
Active
Primary Active Transport
Secondary Active Transport
Movement along a concentration or electrochemical gradient
Rate of diffusion is directly proportional to
Electrochemical gradient
Hydrophobicity
Temperature
Simple Diffusion
Source: Lehninger 5th edition
Source: Lehninger 5th edition
Need for Facilitated transport ?(transport proteins)
Facilitatory transport proteins can be…Carrier proteins:
High stereo specificity.
Transport rates very low than diffusion.
Transporter saturation.
Channel proteins:
Low stereo specificity.
Transport rates comparable to diffusion.
No transporter saturation.
Can be gated.
Lehninger 5th edition
Eg. Glucose Transporter (GLUT)
Eg. Voltage gated K+ channel
Active Transport – against electrochemical gradient
Primary Active Transport:
The endergonic reaction is coupled to exergonic chemical reaction.
ATP ADP + Pi
Lehninger’s Textbook of Biochemistry, 5thed
Eg. Sodium Potassium ATPase
Secondary Active TransportThe transport through one
tranporter is coupled to active transport in another
Lehninger’s Textbook of Biochemistry, 5thed
Eg. Sodium – Glucose Co-transporter
Directional transport
Eg:
Uniport: Voltage gated ion channels in CNS.
Symport: Na- Glucose transporter in Intestine.
Antiport: Cl-Bicarbonate exchanger in RBCs.
Lehninger’s Textbook of Biochemistry, 5thed
Ionophores
Eg.
Oligomycin
Uncoupler - transports the H+ ions , breaks the ETC.
Valinomycin
Masks the K+ ions, transports it across the membranes. Thereby breaks the electrochemical gradient across the membranes.
Lehninger’s Textbook of Biochemistry, 5thed
Solvent Transport
AquaporinsOsmosis
Lehninger’s Textbook of Biochemistry, 5thed
Aquaporins
Macromolecular (Vesicular) Transport
Exocytosis
Involvement of Synaptobrevin and Syntaxin.
Under the control of membrane potential
Eg. Neurotransmitter release.
Endocytosis
- Phagocytosis
- Fluid phase Endocytosis (Pinocytosis)
Receptor mediated endocytosis. – Selective uptake of specific molecules
Eg. LDL intake into hepatic cells.
Thank You!
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