What do endocytosis and exocytosis both require

Macrophages are a type of white blood cell that play a central role in protecting mammals against pathogens like bacteria and viruses. Next, the macrophage will form a vesicle around the virus, completely ingesting it. The vesicle then travels to the cytosol and fuses with the lysosome, where the virus is broken down. Exocytosis is the process by which cells move materials from within the cell into the extracellular fluid. Exocytosis occurs when a vesicle fuses with the plasma membrane, allowing its contents to be released outside the cell.

Exocytosis serves the following purposes:. The majority of molecules traveling to the plasma membrane do so using this pathway. Exocytosis involves the passage of a vesicle from the endoplasmic reticulum or Golgi apparatus, through the cytoplasm to the cell membrane, where it fuses and releases its contents. Once the white blood cell has engulfed a foreign pathogen eliminate it, certain parts of the pathogen are no longer needed.

The macrophage gets rid of this waste material through exocytosis, during which vesicles carry out the unwanted pathogen material. Why is bulk transport important for cells? What is endocytosis? Endocytosis definition and purposes Endocytosis is the process by which cells take in substances from outside of the cell by engulfing them in a vesicle. Endocytosis serves many purposes, including: Taking in nutrients for cellular growth, function and repair: Cells need materials like proteins and lipids to function.

Capturing pathogens or other unknown substances that may endanger the organism: When pathogens like bacteria are identified by the immune system, they are engulfed by immune cells to be destroyed. Disposing of old or damaged cells: Cells must be safely disposed of when they stop functioning properly to prevent damage to other cells. These cells are eliminated through endocytosis. Instead, it will stay in those fluids and increase in concentration. Some human diseases are caused by the failure of receptor-mediated endocytosis.

In the human genetic disease familial hypercholesterolemia, the LDL receptors are defective or missing entirely. People with this condition have life-threatening levels of cholesterol in their blood, because their cells cannot clear LDL particles from their blood. Although receptor-mediated endocytosis is designed to bring specific substances that are normally found in the extracellular fluid into the cell, other substances may gain entry into the cell at the same site.

Flu viruses, diphtheria, and cholera toxin all have sites that cross-react with normal receptor-binding sites and gain entry into cells. The reverse process of moving material into a cell is the process of exocytosis.

Exocytosis is the opposite of the processes discussed in the last section in that its purpose is to expel material from the cell into the extracellular fluid. Waste material is enveloped in a membrane and fuses with the interior of the plasma membrane. This fusion opens the membranous envelope on the exterior of the cell, and the waste material is expelled into the extracellular space Figure 4.

Other examples of cells releasing molecules via exocytosis include the secretion of proteins of the extracellular matrix and secretion of neurotransmitters into the synaptic cleft by synaptic vesicles. Figure 4. In exocytosis, vesicles containing substances fuse with the plasma membrane. The contents are then released to the exterior of the cell. A summary of the cellular transport methods discussed is contained in Table 1, which also includes the energy requirements and materials transported by each.

Cells perform three main types of endocytosis. Phagocytosis is the process by which cells ingest large particles, including other cells, by enclosing the particles in an extension of the cell membrane and budding off a new vacuole. During pinocytosis, cells take in molecules such as water from the extracellular fluid.

Finally, receptor-mediated endocytosis is a targeted version of endocytosis where receptor proteins in the plasma membrane ensure only specific, targeted substances are brought into the cell. Exocytosis in many ways is the reverse process from endocytosis. Here cells expel material through the fusion of vesicles with the plasma membrane and subsequent dumping of their content into the extracellular fluid.

There are three types of endocytosis: phagocytosis , pinocytosis , and receptor-mediated endocytosis. Like phagocytosis, pinocytosis is a non-specific process in which the cell takes in whatever solutes that are dissolved in the liquid it envelops. Unlike phagocytosis and pinocytosis, receptor-mediated endocytosis is an extremely selective process of importing materials into the cell. This specificity is mediated by receptor proteins located on depressed areas of the cell membrane called coated pits.

The cytosolic surface of coated pits is covered by coat proteins. Once bound, the coated pit on which the bound receptor protein is located then invaginates , or pinches in, to form a coated vesicle. Similar to the digestive process in non-specific phagocytosis, this coated vesicle then fuses with a lysosome to digest the engulfed material and release it into the cytosol.