Think About It

An important characteristic of proteins is their ability to change conformation in response to the binding or dissociation of a ligand (see chapter 2). Explain how this characteristic is essential to carrier-mediated transport.

Glucose Binding Protein Conformation

Figure 3.20 Secondary Active Transport. At the basal surface of the cell, an Na -K pump removes sodium ions from the cytoplasm, maintaining a low sodium concentration within the cell. At the apical surface, sodium enters the cell by facilitated diffusion, following its concentration gradient. It can gain entry to the cell only by binding to a carrier, the sodium-glucose transport protein (SGLT), which simultaneously binds and transports glucose. The SGLT does not consume ATP, but does depend on the ATP-consuming pump at the base of the cell.

Figure 3.20 Secondary Active Transport. At the basal surface of the cell, an Na -K pump removes sodium ions from the cytoplasm, maintaining a low sodium concentration within the cell. At the apical surface, sodium enters the cell by facilitated diffusion, following its concentration gradient. It can gain entry to the cell only by binding to a carrier, the sodium-glucose transport protein (SGLT), which simultaneously binds and transports glucose. The SGLT does not consume ATP, but does depend on the ATP-consuming pump at the base of the cell.

Saladin: Anatomy & I 3. Cellular Form and I Text I © The McGraw-Hill

Physiology: The Unity of Function Companies, 2003 Form and Function, Third Edition

112 Part One Organization of the Body

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