Endocytosis: Definition, Types & Examples

Endocytosis: Definition, Types & Examples
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  • 0:00 What is Endocytosis?
  • 1:55 Pinocytosis (Cell Drinking)
  • 2:45 Phagocytosis (Cell Eating)
  • 3:26 Receptor Mediated Endocytosis
  • 4:15 Lesson Summary
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Lesson Transcript
Instructor: Joanne Abramson

Joanne has taught middle school and high school science for more than ten years and has a master's degree in education.

Discover how cells 'eat' and 'drink' without having hands or a mouth! Read about the various ways in which cells accomplish this, and take a quiz to test your understanding.

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.

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