A certain membrane protein allows phosphate groups to enter...

A certain membrane protein allows phosphate groups to enter a eukaryotic cell. (a) Would you expect the protein to function more like KesA or more like GLUT1? (b) Phosphate ions enter the cell along with $\mathrm{H}^{+}$ ions. Describe this transport system using the terms introduced in Fig. $10-15 .$ (c) The eukaryotic intracellular pH is typically slightly lower than the extracellular pH. Does this suggest that the phosphate transporter carries out secondary active transport?

Key Concepts

Membrane Transport Proteins

Membrane transport proteins are integral proteins that facilitate the movement of substances across cell membranes. They come in several types, including channels, carriers, and pumps, each allowing specific molecules or ions to move in response to concentration and/or electrical gradients.

Facilitated Diffusion

Facilitated diffusion is a passive transport mechanism in which substances move down their concentration gradients through specific protein channels or carriers without the direct expenditure of metabolic energy. This process is typically used by molecules that cannot diffuse freely through the lipid bilayer due to size or polarity.

Secondary Active Transport

Secondary active transport is a mechanism that uses the energy stored in the form of ionic gradients—established by primary active transport—to move molecules against their concentration gradient. This process does not directly use ATP but is driven by the flow of ions down their electrochemical gradient.

Symport (Cotransport Mechanism)

Symport is a form of secondary active transport where two different molecules or ions are simultaneously transported across a membrane in the same direction. One molecule’s movement down its gradient provides the energy required to transport the other molecule up its gradient.

Electrochemical Gradient

The electrochemical gradient refers to the difference in both charge and concentration of an ion across a membrane. This gradient is fundamental in driving various types of transport, including secondary active transport, as it provides the potential energy necessary for moving substances against their concentration gradient.

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