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Peripheral Proteins: Definition & Function

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  • 0:00 What are Peripheral Proteins?
  • 1:17 Multifunctional…
  • 5:10 Lesson Summary
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Lesson Transcript
Instructor: Erika Steele

Erika has taught college Biology, Microbiology, and Environmental Science. She has a PhD in Science Education.

The cell's membrane is made of a variety of lipids and proteins. In this lesson, we will focus on the roles the peripheral proteins play in the cell and in human diseases.

What Are Peripheral Proteins?

Most molecules cannot cross cell membranes alone because it is impenetrable to them. The role of the plasma membrane is to form a barrier and protect the cell from the environment. The problem is, the cell membrane is a bit overzealous at its job. If it were up to the cell membrane, hardly anything would get in or out of the cell. This is counterproductive if the cell is going to stay alive since the cell membrane blocks vital molecules from crossing. Think of the plasma membrane as a dumb dictator whom you cannot reason with. For this reason, the cell membrane is full of proteins that help keep the plasma membrane and other membranes in the cell in check.

There are two types of membrane proteins: integral and peripheral. Think of proteins as diplomats who can reason with cell membranes and form ways to bring molecules into the cell. There are two ways a protein can attach to the plasma membrane as depicted in Figure 2 (see video).

Peripheral proteins don't cross the membrane. They kind of hang out on either side of cell membranes. They are loosely attached to other proteins or the membrane itself through hydrogen bonds. They're called 'peripheral proteins' because they sit on the outside of the membrane and do not integrate into the membrane.

Multifunction Membrane Proteins

Even though peripheral membranes don't form entryways to the cell since they don't penetrate the membrane, they're really vital to the function of the cell. Think of them as the wingmen of the membrane proteins since they play vital roles for the cell. They do this by acting as partners with other proteins. Peripheral membrane proteins serve multiple roles including:

Transportation

Peripheral membranes allow many molecules to be carried around the cell. Some peripheral membrane proteins carry molecules between other proteins. As shown in Figure 3 (see video), the function of cytochrome c is to carry electrons from one protein to the next. If cytochrome c was not present, the proteins that aid in generating energy would not obtain the electrons necessary to generate energy in the cell's mitochondria.

You couldn't exist if your cells didn't have this protein on the membranes of the mitochondria in your cells. Cytochrome c helps transport electrons to generate energy in the mitochondria. The other proteins that produce the energy couldn't do their jobs without cytochrome c acting as a wingman to bring electrons to them in order to produce energy.

Cytochrome c is released from the membranes of the mitochondria when a cell becomes damaged and can't be repaired. Released cytochrome c signals a cascade of proteins that lead to cell death. When this does not happen, cells with damaged DNA are allowed to replicate, which leads to cancer.

When a cell gets old or its DNA becomes damaged, cytochrome c is released from the membrane and signals to the cell that it needs to die as shown in Figure 4. A good wingman knows when to tell their partner to give up. In some cancer cells, this does not happen, and cells with damaged DNA are allowed to grow out of control and form tumors. So cytochrome c is a peripheral protein, that is essential for life and for health, but we never even think about it.

Anchoring

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