Vesicles are tiny sacs that transport material within or outside the cell. There are several types of vesicle, including transport vesicles, secretory vesicles, and lysosomes.
This article will focus on the functions of vesicles and the different types that are present within the body.
A vesicle is a self-contained structure consisting of fluid or gas surrounded and enclosed by an outer membrane called the lipid bilayer. This is made up of hydrophilic heads and hydrophobic tails that cluster together.
Thinking of a vesicle as a tiny bubble that stores and transports materials may help people get an idea of how they look and function within a cell.
Each vesicle type has a different function, and different vesicles are necessary for different biological processes.
Vesicles can help transport materials that an organism needs to survive and recycle waste materials. They can also absorb and destroy toxic substances and pathogens to prevent cell damage and infection.
Although they are similar to vacuoles, which also store materials, vesicles have their own unique functions and abilities. For example, they can fuse with the membranes of other cells to carry out a specific role, such as breaking down another cell.
Vesicles also help store and transport materials such as proteins, enzymes, hormones, and neurotransmitters. They are a small but essential part of biological systems and processes such as:
- digestion and metabolism
- the nervous system
- kidney and liver function
Vesicles can carry out many functions in organisms. There are five main types of vesicle, and each has its own function.
Learn more about the types of vesicle below.
Transport vesicles help move materials, such as proteins and other molecules, from one part of a cell to another.
When a cell makes proteins, transporter vesicles help move these proteins to the Golgi apparatus for further sorting and refining. The Golgi apparatus identifies specific types of transport vesicle then directs them to where they are needed.
Some proteins in the transporter vesicles could, for example, be antibodies. So, the Golgi apparatus would package them into secretory vesicles to be released outside of the cell to fight a pathogen.
Some scientists refer to the Golgi apparatus as the cell’s “post office.”
Lysosomes are vesicles that contain digestive enzymes. They are only present in animal cells. They function as part of the cell’s recycling system and can also help initiate cell death.
When a cell needs to recycle large molecules, lysosomes release their enzymes to break down these bigger molecules into smaller ones. When they have broken up the larger matter, the cell can recycle what is left.
If a cell has absorbed something harmful, such as a pathogen, it can use its lysosomes to ingest those bacteria and destroy them with enzymes.
Scientists are still not sure why lysosomes can survive, given that they are filled with enzymes that can break down cells just like themselves.
Secretory vesicles play an important role in moving molecules outside of the cell, through a process called exocytosis. They are crucial for healthy organ and tissue function. For example, secretory vesicles in the stomach will transport protein-digesting enzymes to help break down food.
Synaptic vesicles are another example of a secretory vesicle, and they are present at the end of nerve cells (neurons).
These vesicles help transmit signals from one nerve cell to another by releasing or secreting neurotransmitters that activate receptors in the next cell along. They are a tiny 30–40 nanometers in diameter.
Like lysosomes, peroxisomes contain digestive enzymes. They use enzymes to digest excess nutrients in a cell, such as fatty acids. Peroxisomes also break down alcohol.
Peroxisomes also use an enzyme to break hydrogen peroxide into water and oxygen, which are both harmless and useful to the cell’s function.
Peroxisomes can vary in shape and size, depending on the needs of the cell they serve. They will sometimes increase in number and size if, for example, they have a lot of alcohol to break down.
Extracellular vesicles can float outside of cells.
For many years, scientists saw extracellular vesicles as insignificant to cell health and functionality. However, recent research has suggested that these vesicles have a vital role to play in communicating between cells and have important evolutionary consequences.
A 2019 literature review in the journal PLOS Biology discusses how viruses and bacteria may be able to interact with healthy cells via extracellular vesicles.
However, more research is necessary to understand why and how this happens.
Vesicles are a crucial part of the cell and play important roles in many biological processes.
The five main types of vesicle are:
- transport vesicles
- secretory vesicles
- extracellular vesicles
Each vesicle type has a particular function — be it transporting proteins within or outside the cell or absorbing and dissolving a pathogen that enters the cell.