Learn about endocytosis. Understand what endocytosis is, learn the purpose of this process, identify the types of endocytosis, and see examples of endocytosis.
Updated: 02/15/2022
Types and Description of Endocytosis
What Is Endocytosis?
Endocytosis is a process that cells use to take in materials from their environment. The word ''endocytosis'' comes from the Greek. The Greek root endon means within. The Greek word kytos means cell, and the suffix -osi means process. Thus, the endocytosis definition in biology is a process where the cell takes things in.
During endocytosis, the cell membrane, also known as the plasma membrane, invaginates and takes in extracellular substances in a small sphere called an endocytic vesicle. Endocytosis relies on endocytic vesicles, small spheres that bud inwards from the cell membrane, in order to carry out endocytosis. Endocytosis also uses another internal organelle called a lysosome. Lysosomes are digestive organelles and help break down the contents of the vesicles.
Endocytosis is a type of membrane transport, where molecules are brought into or out of the cell. Endocytosis is a type of active transport, meaning it requires energy. Other types of transport, such as diffusion, do not require energy and are called passive transport. During diffusion, no vesicles are used, but rather materials diffuse directly into and out of the cell through the cell membrane.
What Is The Purpose of Endocytosis?
The main purpose of endocytosis is to take in extracellular materials to the cell. Some examples of the function of endocytosis include:
- Destruction of pathogens
- Presentation of antigens to activate the immune system
- Taking in nutrients and water from the environment
- Regulating the composition of the cell membrane
Endocytosis is important to allow cells to take in large molecules, both solid and liquid, from the environment. Endocytosis plays an important role in many organ systems to help maintain homeostasis, or a balance in the body. For example, the immune system uses endocytosis to clear pathogens from the body. Endocytosis also allows cells to uptake nutrients from the environment and control the composition of the cell membrane.
Types of Endocytosis
There are three main types of endocytosis:
- Pinocytosis
- Phagocytosis
- Receptor-mediated endocytosis
Pinocytosis is sometimes referred to as ''cell drinking'', due to the Greek root word pino, meaning to drink. During pinocytosis, the cell takes in nutrients dissolved in the extracellular fluids in small vesicles. There are two main types of pinocytosis, micropinocytosis and macropinocytosis. In micropinocytosis the vesicles taken in are smaller than 0.1 micron in diameter. Micropinocytosis is important in the caveolae of endothelial cells. This region of the cell membrane is specialized to perform micropinocytosis and functions in cell signaling and maintaining a specific membrane lipid composition. In macropinocytosis, the vesicles are between 0.5 and 5 microns in diameter. Macropinocytosis is important in white blood cells where they are formed from extensions of the cell membrane called villi.
Comparing endocytosis vs phagocytosis is done by understanding that phagocytosis is a type of endocytosis. Phagocytosis is known as ''cell eating'', as the Greek root phago means to eat. During phagocytosis the cell sends out large extensions of the cell membrane and engulfs particles in the extracellular environment. Phagocytosis is important for immune cells like macrophages. These cells patrol the tissues of the body, looking for pathogens. When a pathogen is found, the cell can engulf it with phagocytosis and alert the rest of the immune system.
During receptor mediated endocytosis receptor proteins on the cell membrane bind directly to the molecules that will be taken in through endocytosis. Receptor mediated endocytosis is also known as clathrin coated endocytosis because the protein clathrin is essential in forming the vesicle. During receptor mediated endocytosis, a cascade of signaling molecules leads to the invagination of parts of the membrane that include the protein clathrin. This creates divots in the membrane, called clathrin coated pits. On the extracellular face of these areas of the membrane are receptors that bind to their target cargo. Once the molecules are bound to the receptors, the vesicle can invaginate and be brought into the cell.
Endocytosis Process
The endocytosis process is different depending on which type of endocytosis is occurring. However, there are three main common steps in all of the types.
- First, the cell membrane invaginates and forms a cavity that can be filled with the extracellular substances, such as water, nutrients, hormones, proteins or other molecules.
- Next, the cell membrane folds together, forming a vesicle that traps the extracellular substances within.
- Lastly, the ends of the membrane fuse together and the vesicle pinches off from the plasma membrane and enters the cell. From here it can be processed through a variety of pathways in the cell's endomembrane system.
What Is Endocytosis?
Just as you need to eat and drink, your cells need to eat and drink. And, just like you are covered with skin, your cells are covered by a cell membrane. And, just like your skin, it is the cell membrane's job to keep things outside of it. Okay, the process of diffusion does let some things cross the cell membrane, like water, small molecules, and molecules without a charge. I admit the analogy falls apart here, but stay with me anyway.
But, what if the cell wants that large molecule that is outside of it to be inside of it? If you see a cheeseburger outside of you, and you want it inside of you, you eat it! But, a cell does not have a mouth. So now what? This is where the process of endocytosis comes into play.
Endocytosis is from the Greek roots endon, meaning within; kytos, meaning cell; and -osis, meaning process. So, it is the process by which a substance is brought inside a cell without having to pass through the cell membrane. By the way, exocytosis is the opposite of endocytosis, the process by which substances exit the cell without having to pass through the cell membrane.
I should make a point here. Endocytosis, unlike diffusion, requires energy from the cell. To keep with the analogy of your skin, you can passively soak up the sun's rays. You just have to lie there, and the tanning can happen while you're asleep. However, to eat a cheeseburger, you have to expend energy to grab it, bite it, chew, and digest it. Same with the cell. Water diffuses through the membrane passively; the cell does not have to expend energy. However, if the cell wants that large molecule, it has to expend energy to grab it and bring it in.
There are three types of endocytosis: pinocytosis, phagocytosis, and receptor mediated endocytosis.
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Endocytosis Examples
There are many examples of endocytosis. For example, phagocytosis is essential for immune system function, and receptor mediated endocytosis helps to regulate cholesterol levels in the blood. Each of these examples are discussed in more detail below.
Pathogens
Unlike other kinds of endocytosis, not all cells can do phagocytosis. In the human body, only phagocytes are capable of this type of endocytosis. Phagocytes are specialized cells inside multicellular organisms, like humans, that are able to engulf other cells. Examples of phagocytic cells in the human body include: monocytes, macrophages, neutrophils, dendritic cells, osteoclasts, and eosinophils. These cells remove both pathogens from the body as well as cells that have gone through programmed cell death, called apoptosis.
Specialized receptors on the surface of phagocytes recognize cells as targets to be ingested. When a target cell is recognized, a signaling cascade is set off inside the cell that allows for remodeling of the cytoskeleton to extend the cell membrane out around the target with projections called pseudopodia. Then, the cell membrane ends fuse together, encapsulating the target cell in a vesicle. The vesicle buds off and enters the endomembrane system. Here, it can fuse with another organelle called a lysosome. The lysosome contains enzymes and acids necessary to break down the contents of the vesicle.
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Low Density Lipoprotein (LDL)
Low density lipoprotein (LDL) is a type of transport protein that moves fats around the body. LDL is sometimes referred to as "bad cholesterol" because it leads to build up of cholesterol on the artery walls, which can lead to a wide variety of cardiovascular problems. LDL is rounded up by cells and removed from the blood through the use of receptor mediated endocytosis. In this process, LDL binds to LDL receptors in clathrin coated pits on the cell membrane. The LDL is taken into the cell through the vesicle and enters the lysosome. The lysosome breaks down the LDL and releases free cholesterol which can be used in the cell membrane or in other functions.
Lesson Summary
Endocytosis is a process where cells take in molecules from their environment using vesicles made from the plasma membrane. Endocytosis uses invaginations of the plasma membrane, called vesicles, which ultimately fuse with the lysosome, a digestive organelle needed to break down the contents of the vesicle. Endocytosis is a type of active transport, which uses energy to move molecules across the membrane. This is in contrast to processes like diffusion, which move molecules directly through the membrane without using energy.
There are three kinds of endocytosis. Pinocytosis is referred to as ''cell drinking'' and includes the cell taking up dissolved nutrients in small vesicles. Phagocytosis is ''cell eating'' and involves only certain specialized cells called phagocytes engulfing other cells in the body. Receptor mediated endocytosis involves specific substances binding to receptor proteins and being engulfed into the cell in clathrin coated vesicles. An important example of receptor mediated endocytosis is low density lipoprotein (LDL) being taken up and recycled in this way.
Pinocytosis (Cell Drinking)
The Greek word pino means to drink. Pinocytosis is the process by which the cell takes in fluids (as well as any small molecules dissolved in those fluids). You can remember that pinocytosis is cell drinking by thinking about the wine that we drink, pinot grigio.
In the process of pinocytosis, the cell membrane folds in on itself, creating a small pocket, or pouch. The cell membrane closes around this little pocket, forming what's called a vesicle. Any liquids or small molecules that were trapped in that pocket are taken into the cell. The vesicle fuses with a lysosome, whose digestive enzymes break down the molecules so that its parts can be recycled. Lyse, by the way, is from the Greek lusis, meaning 'loosen' or 'break up.'
Phagocytosis (Cell Eating)
Phago- comes from the Greek word phagein, meaning to eat. Phagocytosis is the process by which cells engulf and digest large molecules. The cell sends out projections of its cytoplasm called pseudopodia, Greek for 'false feet.' The pseudopodia engulf the molecule, and the cell membrane fuses around, trapping it inside a cellular vesicle. The vesicle again joins with a lysosome, and the molecule is broken down.
Not all cells go through this process. Amoebae, white blood cells, and other cells that are able to change their shape are examples of cells that do conduct phagocytosis.
Receptor Mediated Endocytosis
Receptor mediated endocytosis is utilized when there are very specific substances that the cell requires. It is similar to pinocytosis, but the in-folding of the cell membrane is triggered only when the target molecules bind to receptors on the outside of the cell.
Receptor mediated endocytosis is the primary way that our body processes LDL, low-density lipoprotein, or the 'bad' cholesterol (called 'bad' since too much can lead to blocked arteries). Receptors on the outside of the cell membrane bind to a protein in the membrane of LDL. This binding initiates endocytosis. Once the LDL has been digested by the enzymes of the lysosome, the amino acids, cholesterol, and fatty acids are released into the cytoplasm. Once there, they can either be recycled or excreted from the cell.
Lesson Summary
While some molecules can easily pass in and out of the cell membrane through diffusion, the cell must make an effort to acquire other molecules. One of the ways the cell does this is through endocytosis, the process of bringing molecules into the cell without having them cross the cell membrane.
There are three types of endocytosis: pinocytosis, phagocytosis, and receptor mediated endocytosis. Each type of endocytosis involves encapsulating the target molecule in a pocket of cell membrane called a vesicle and bringing it to the lysosome so that it can be broken down.
Pinocytosis (cell drinking), traps liquids and any small molecules dissolved in the liquid. Phagocytosis (cell eating), involves wrapping projections of cell cytoplasm (pseudopodia) around large molecules. Only cells that have the ability to change shape conduct phagocytosis. In receptor mediated endocytosis, endocytosis only occurs after target molecules have bonded with receptors in the cell membrane.
Important Definitions
 |
| Main Terms | Definitions |
|---|---|
| Endocytosis | one way in which a cell membrane allows some molecules into a cell |
| Vesicle | a pocket in the cell membrane that targets a molecule and brings it down to the lysosome |
| Pinocytosis | captures liquids and molecules broken up in liquids |
| Phagocytosis | involves wrapping cell cytoplasm around large molecules |
| Receptor Mediated Endocytosis | this type of endocytosis happens after specific molecules have bonded with receptors |
Learning Outcomes
When this lesson ends, students should be able to:
- State the definition of endocytosis
- Identify and expound upon the three types of endocytosis
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Video Transcript
What Is Endocytosis?
Just as you need to eat and drink, your cells need to eat and drink. And, just like you are covered with skin, your cells are covered by a cell membrane. And, just like your skin, it is the cell membrane's job to keep things outside of it. Okay, the process of diffusion does let some things cross the cell membrane, like water, small molecules, and molecules without a charge. I admit the analogy falls apart here, but stay with me anyway.
But, what if the cell wants that large molecule that is outside of it to be inside of it? If you see a cheeseburger outside of you, and you want it inside of you, you eat it! But, a cell does not have a mouth. So now what? This is where the process of endocytosis comes into play.
Endocytosis is from the Greek roots endon, meaning within; kytos, meaning cell; and -osis, meaning process. So, it is the process by which a substance is brought inside a cell without having to pass through the cell membrane. By the way, exocytosis is the opposite of endocytosis, the process by which substances exit the cell without having to pass through the cell membrane.
I should make a point here. Endocytosis, unlike diffusion, requires energy from the cell. To keep with the analogy of your skin, you can passively soak up the sun's rays. You just have to lie there, and the tanning can happen while you're asleep. However, to eat a cheeseburger, you have to expend energy to grab it, bite it, chew, and digest it. Same with the cell. Water diffuses through the membrane passively; the cell does not have to expend energy. However, if the cell wants that large molecule, it has to expend energy to grab it and bring it in.
There are three types of endocytosis: pinocytosis, phagocytosis, and receptor mediated endocytosis.
Pinocytosis (Cell Drinking)
The Greek word pino means to drink. Pinocytosis is the process by which the cell takes in fluids (as well as any small molecules dissolved in those fluids). You can remember that pinocytosis is cell drinking by thinking about the wine that we drink, pinot grigio.
In the process of pinocytosis, the cell membrane folds in on itself, creating a small pocket, or pouch. The cell membrane closes around this little pocket, forming what's called a vesicle. Any liquids or small molecules that were trapped in that pocket are taken into the cell. The vesicle fuses with a lysosome, whose digestive enzymes break down the molecules so that its parts can be recycled. Lyse, by the way, is from the Greek lusis, meaning 'loosen' or 'break up.'
Phagocytosis (Cell Eating)
Phago- comes from the Greek word phagein, meaning to eat. Phagocytosis is the process by which cells engulf and digest large molecules. The cell sends out projections of its cytoplasm called pseudopodia, Greek for 'false feet.' The pseudopodia engulf the molecule, and the cell membrane fuses around, trapping it inside a cellular vesicle. The vesicle again joins with a lysosome, and the molecule is broken down.
Not all cells go through this process. Amoebae, white blood cells, and other cells that are able to change their shape are examples of cells that do conduct phagocytosis.
Receptor Mediated Endocytosis
Receptor mediated endocytosis is utilized when there are very specific substances that the cell requires. It is similar to pinocytosis, but the in-folding of the cell membrane is triggered only when the target molecules bind to receptors on the outside of the cell.
Receptor mediated endocytosis is the primary way that our body processes LDL, low-density lipoprotein, or the 'bad' cholesterol (called 'bad' since too much can lead to blocked arteries). Receptors on the outside of the cell membrane bind to a protein in the membrane of LDL. This binding initiates endocytosis. Once the LDL has been digested by the enzymes of the lysosome, the amino acids, cholesterol, and fatty acids are released into the cytoplasm. Once there, they can either be recycled or excreted from the cell.
Lesson Summary
While some molecules can easily pass in and out of the cell membrane through diffusion, the cell must make an effort to acquire other molecules. One of the ways the cell does this is through endocytosis, the process of bringing molecules into the cell without having them cross the cell membrane.
There are three types of endocytosis: pinocytosis, phagocytosis, and receptor mediated endocytosis. Each type of endocytosis involves encapsulating the target molecule in a pocket of cell membrane called a vesicle and bringing it to the lysosome so that it can be broken down.
Pinocytosis (cell drinking), traps liquids and any small molecules dissolved in the liquid. Phagocytosis (cell eating), involves wrapping projections of cell cytoplasm (pseudopodia) around large molecules. Only cells that have the ability to change shape conduct phagocytosis. In receptor mediated endocytosis, endocytosis only occurs after target molecules have bonded with receptors in the cell membrane.
Important Definitions
|
| Main Terms | Definitions |
|---|---|
| Endocytosis | one way in which a cell membrane allows some molecules into a cell |
| Vesicle | a pocket in the cell membrane that targets a molecule and brings it down to the lysosome |
| Pinocytosis | captures liquids and molecules broken up in liquids |
| Phagocytosis | involves wrapping cell cytoplasm around large molecules |
| Receptor Mediated Endocytosis | this type of endocytosis happens after specific molecules have bonded with receptors |
Learning Outcomes
When this lesson ends, students should be able to:
- State the definition of endocytosis
- Identify and expound upon the three types of endocytosis
To unlock this lesson you must be a Study.com Member.
Create your account
Frequently Asked Questions
What are the steps of endocytosis?
The steps of endocytosis include first creating an invagination of the cell membrane that creates a fluid filled pocket. The membrane then folds inward, connecting and creating a vesicle. The vesicle then moves into the cell, separating from the cell membrane.
What does endocytosis mean in simple terms?
Endocytosis is the process that cells use to take in materials from their environment. Endocytosis can be used to take in both solids and liquids.
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