Bosh miya yarim sharining po’stloq qismi, uning tuzilishi. Reja

the coupled transport of substances can occur in the same direction

(cotransport) or in opposite directions (countertransport) (Fig. 1.14).

For instance, in the kidney the transport of amino acids is coupled

with an active Na+ transport. Additionally, active ion transport through

cell membranes is necessary for the formation of membrane or resting

potentials.

Endocytosis and Exocytosis

Large molecules, such as proteins, enter (endocytosis) or exit (exocytosis)

through the cell membrane by so-called vesicular transport (Fig. 1.16).

During this process, substances are attached in part to the outside of the

cell by membrane-bound receptors, enclosed by a part of the plasma

membrane, and moved into the interior of the cell as a membranewrapped