Transport of substances across the plasma membrane by vesicles

2021-06-12 10:39 PM

In the cytoplasm, the endocytosis vesicles will mix with the lysosomes, and the endoplasmic reticulum components will be hydrolyzed by enzymes.

This is a form of transport that allows large particles to pass through the cell membrane. This form includes:

(1) Endocytosis includes phagocytosis, pinocytosis, and receptor-mediated endocytosis.

(2) Exocytosis

The phenomenon of endocytosis

The extracellular material is introduced into the vesicles formed by the indentation of the cell membrane

In the cytoplasm, the endocytosis vesicles will mix with the lysosomes, the endoplasmic reticulum components will be hydrolyzed by enzymes and the monomers will be introduced into the intracellular fluid.

Phenomenon of phagocytosis

Figure: Phagocytosis.

1: bacteria or a foreign body; 2: sham; 3: phagocytic vesicle; 4: cytoplasmic membrane.

The cytoplasm and cell membrane form pseudocysts that embrace an object outside the cell to bury it in the cytoplasm, where the object is encased in a membrane that originates from the cytoplasmic membrane and is called a vesicle. phagocytic vesicle or phagosome.

Only a few cells in the body perform the function of phagocytosis. The most important phagocytes are neutrophils and macrophages. The phenomenon of phagocytosis helps to bring bacteria, cell debris into the cells capable of phagocytosis.

Humidity phenomenon

The phenomenon by which extracellular fluids and soluble molecules outside the cell are introduced into the cell. This is a function found in all types of cells in the body.

Hygrocytosis is accomplished simply through the infiltration of the cytoplasmic membrane to form a pinocytic vesicle that carries fluid particles into the cytoplasm.

Receptor-mediated endocytosis

This phenomenon is similar to hygrocytosis but is highly selective, in that the cell selects specific molecules or objects to be introduced into the cytoplasm, so that despite their concentration in Extracellular fluid is very low, but they can still enter the cell through transmembrane proteins that act as specific receptors for them on the plasma membrane.

Substances that have affinity for a specific receptor are called ligands, these can be cholesterol, iron and vitamins that are essential for cellular metabolism or hormones, etc., but sometimes these are also entry of some viruses, including human immunodeficiency virus (HIV). 

Figure: Receptor-mediated endocytosis.

a: ligand; b: receptors; c: digestive enzyme; d: degraded ligand.

The import process takes place according to the following steps

(1) Ligand binds to its specific receptor on the outside of the plasma membrane.

(2) This binding causes the plasma membrane region at the site of the ligand-receptor complex to concave to form an endocytosis vesicle carrying the above complex.

(3) In the cytoplasm, endocytosis vesicles fuse together to form a larger structure called an endosome.

(4) In the endosome the receptors separate from the ligands and divide into two parts, the endosome containing only receptors and the endosome containing only ligands.

(5) The endosome containing the receptors will reintegrate with the plasma membrane to continue the task.

(6) The endosome containing ligands will integrate with the lysosomes and the enzymes of this organelle will break down the ligands to use for other cellular activities. 

The phenomenon of cell shedding

Cytoplasmic discharge is the phenomenon in which structures called secretory vesicles are formed in the cytoplasmic lumen and move forward and fuse the membrane of the vesicle into the plasma membrane to bring the contents of the vesicle into the extracellular fluid. .