Vesicles are bubble-like organelles that are made of a membrane and are full of fluid. Vesicles have a lot of important jobs in the cell. In some ways, they are like the trucks that carry food and supplies across the country. For a vesicle, the country is a cell!
The outside membrane of a vesicle contains the same materials as the cell membrane. In some cases, the vesicle even forms by pinching off from the cell membrane! The fluid on the inside is usually a small amount of cytoplasm or fluid from right outside of the cell.
A vesicle forms from the plasma membrane during endocytosis.
Transport vesicles are responsible for moving materials between the cell’s organelles. The most common path for them to take is from the endoplasmic reticulum to the golgi apparatus. They package up proteins manufactured in the ribosomes of the endoplasmic reticulum. They then move across the cell by following the tracks provided by the cell’s microtubules.
Vesicles are pulled along the microtubules by special motor proteins. When they get to the golgi apparatus, they can combine with the golgi’s membrane. This lets them release the proteins into the golgi.
A motor protein pulls a vesicle along a microtubule.
Sometimes proteins need to be transported to different parts of the golgi apparatus. Transport vesicles can form from the membrane of part of the golgi apparatus. They can then carry proteins to a different part! When the golgi finishes working on the proteins, it can release them back into the cell. If the protein is staying inside the cell, it is released into another transport vesicle. If it is going outside of the cell, it goes into another type of vesicle called a secretory vesicle.
Vesicles can also transport material that the cell gets from outside of its membrane. A piece of the cell membrane can pinch off into the cell through a process called endocytosis. As a result, this produces a vesicle that contains fluid and molecules from outside of the cell! This material can then be transported to other organelles in the cell. The diagram at the top of this page illustrates endocytosis.
Other Types of Vesicles
Transport vesicles bring proteins to the golgi apparatus. Additionally, the proteins are modified and released in secretory vesicles.
Besides transport vesicles, there are several other types of vesicles. Each of them has a different role in helping the cell store or transport materials. What do they all have in common? They all have one membrane on the outside and fluid on the inside.
Secretory vesicle move materials from the inside of the cell to the outside. If transport vesicles are the cell’s trucks, then secretory vesicles are ships and airplanes. They take material the cell wants to send to the outside world and get it out of the cell. Vacuoles are found in plant cells. They are large vesicles that are mostly used to store water and food. Peroxisomes help the cells produce energy from molecules called fatty acids. Lysosomes are like the cell’s stomach. They contain special proteins called enzymes which can break down food for the cell. They can combine with transport vesicles to help digest whatever is inside.