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What Are Glycoproteins? - Definition, Functions & Examples

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  • 0:03 What Are Glycoproteins?
  • 0:59 Immunology
  • 2:13 Protection
  • 3:15 Communication
  • 3:49 Reproduction
  • 4:20 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb
This lesson is about glycoproteins, the sweet outer coating of cells! Glycoproteins are proteins that have sugars attached to them. They do many important jobs for the body, such as helping the immune, digestive, and reproductive systems.

What Are Glycoproteins?

Proteins are found floating in or around the membrane of cells. They move and can interact with the cell's environment. Glyco is a prefix in science that means 'sugar.' Glycoproteins are simply proteins with a sugar attached to them.

The sugars can be attached to a protein in two locations in the cell, the endoplasmic reticulum, which produces N-linked sugars, and the Golgi apparatus, which produces O-linked sugars. The N-linked glycoproteins have a sugar attached to a nitrogen atom, and O-linked glycoproteins have a sugar attached to an oxygen atom. The different structure of N- and O-linked sugars give them different functions.

Glycoproteins are always found on the outside of the plasma membrane, with the sugar facing out. This is an image of the plasma membrane with glycoproteins labeled (see video).

Functions

Glycoproteins are involved in nearly every process in cells! They have diverse functions such as in our immune system, protection of our body, communication between cells, and our reproductive systems. Let's examine these functions more closely.

Immunology

White blood cells roll along your blood vessels, looking for potential invaders. The way they attach to the blood vessel lining is through glycoproteins called lectins. Without these, our immune system would be pretty weak, since our white blood cells wouldn't be able to travel the body.

Glycoproteins are also important for red blood cells. Blood type refers to the type of glycoprotein on our red blood cells. If you have type A blood, you have A antigens, or A glycoproteins, on your red blood cells. This helps the body to identify that your blood is part of you and tells it not to attack it. Glycoproteins also help to stimulate the process of coagulation of platelets to clot blood when you get cut. People who are missing important proteins on platelets can't clot their blood and have a disease called hemophilia, where any cut continues to bleed indefinitely.

Protection

Many organs in your body need to secrete mucus to function properly. Examples include your stomach, small intestine, and airways in the lungs. Cells lining these body cavities secrete, or send out, glycoproteins. The sugars mixed with water in your body create a smooth mucus. In the stomach, this mucus helps protect your stomach lining from the harsh acids needed to digest food. In the lungs, the mucus helps to trap bacteria, keeping your lungs clean and healthy!

Glyoproteins are also involved in keeping our skin healthy. Glycoproteins are on the surface of skin cells, called epithelial cells. These help to attach our skin cells to each other, forming a tough barrier to protect our body. Cadherins are an example of a glycoprotein that helps our skin hold together. In the image seen here (see video), the long black lines connecting two skin cells together are types of cadherins. Think of them like glue holding our skin together!

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