Vesicles are small cell organelles that are present in cells. These organelles are small, membrane enclosed sacs which store and transport substances to and from one cell to another and from one part of a cell to another. They are one of the important parts of a cell. The vesicle is separated from the rest of the cytoplasm by at least one phospholipid bilayer. The membrane that encloses the vesicle is similar to the plasma membrane. Thus, vesicles can fuse with the plasma membrane when they want to release their contents outside the boundaries of the cell. However, vesicles can also fuse with other organelles that are present inside the cell to release or engulf substances. The vesicle function in cell, thus, varies depending on the type of vesicle that is present. Given below are details regarding the different types of vesicle present in cells and their corresponding functions.
Vesicle Functions According to Their Type
Lysosomes are specialized organelles which contain digestive enzymes that are used to break down substances in the cell into smaller molecules. As these organelles are present only in animal cell, vesicle function in this case will be different compared to that of plant cell. The lysosome structure consists of small sacs that are bound by a single layered membrane. These are the organelles that are involved with cellular digestion. Hence, lysosomes function consists of eliminating harmful substances from the cell with the help of endocytosis. This is achieved by phagocytosis process.
The vacuole is an organelle that is predominantly present in plant and fungal cells. It is also seen in certain animal and bacterial cells, though it is one of the prominent plant cell parts. These organelles are filled with fluid and basically contain enzymes in solution. The vacuoles are responsible for isolating materials from the cell which may be harmful to it and also, containing waste products within themselves. As an autophagic vesicle, function of this cell organelle is to ingest and destruct any invading bacteria. It is also responsible for maintaining the turgor pressure in the cell and the pH of the cell.
These are membrane bound vesicles which are nothing but secreted proteins and are made on ribosomes which are found in the rough endoplasmic reticulum. Most of these proteins mature in the Golgi apparatus before going to their final location, which may be lysosomes, peroxisomes or some place outside the cell. These proteins are carried from one location to another inside the transport vesicles. Hence, as the name suggests, transport vesicle function is to move molecules between different locations inside the cell.
Secretory vesicles are those vesicles that contain material that is to be excreted from the cell. Thus, these vesicles may contain material that is harmful for the cell, and hence, there is need to get rid of it. So, it may contain waste products or end products of reactions in the cell. These in fact, may even contain many useful secretions that are needed in different parts of the body. There are different types of secretory vesicles, like synaptic vesicles, which are located at pre-synaptic terminals in the neurons. In this type of secretory vesicle, function of the organelle consists of storing neurotransmitters. The hormones that are secreted from the endocrine glands are also stored in secretory vesicles, from where they are released into the bloodstream.
This was all about the different types of vesicles in cells and their functions. There are certain specialized vesicles that are found only in certain cells, like seminal vesicles which are present postero-inferior to the urinary bladder in males. Seminal vesicle function consists of secreting a large proportion of the fluid that eventually becomes a part of semen. In the end, the vesicle function will depend on the type of vesicle that is present in the cell.