Transport of substances

Performing a transport function, plasmolemma provides diffusion (passive transfer) of a number of substances, such as water, ions, some low molecular weight compounds. Other substances penetrate through the membrane by active transport against a concentration gradient with the expenditure of energy due to the splitting of ATP. Since many organic molecules are transported (sugars, amino acids and others.). These processes may involve transport of ions participate in them special carrier proteins.

Large molecules of biopolymers hardly penetrate plasmolemma. In some cases, macromolecules and even their units, and often large particles get into the cell as a result of processes of endocytosis (Fig. 6, A and B). Endocytosis is formally divided into phagocytosis (capture and uptake of large particles, such as bacteria or even fragments of other cells) and pinocytosis (capture macromolecular compounds).

Endocytosis begins with adsorption on the surface plasmolemma absorbed substances. Binding them plasmolemma determined by the presence on its surface receptor molecules. After sorption of substances on the surface of plasmolemma begins to form first small invaginations into the cell. These may take the form invaginations still unclosed rounded vesicles or be a deep intussusception, invagination into the cell. Then such local invagination otshnurovyvayutsya from plasmolemma in the form of bubbles freely positioned underneath.

Plasmolemma participates in the removal of substances from the cells (called exocytosis). In this case, intracellular products (proteins, mucopolysaccharides, fat droplets, and others.) Enclosed in vacuoles or vesicles and delineated from hyaloplasm membrane suitable for plasmolemma. Locations and contacts plasmolemma membrane vacuoles fuse and the contents of the vacuoles released to the environment.

The process of endocytosis and exocytosis carried out with the participation of related plasmolemma of fibrillar cytoplasmic components - such as microtubules and microfilaments cancellable. Recently, with certain portions connecting plasmolemma may have to change their length to pull the membrane into the cell which leads to the separation of plasmolemma endocytic vacuoles. Often, directly adjacent thereto, form a continuous microfilaments, called the cortex.

Не знайшли потрібну інформацію? Скористайтесь пошуком google:

Генерація сторінки за: 0.005 сек.