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.

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