Protein Molecules: Functions, Structure & Examples

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  • 0:00 What Is a Protein Molecule?
  • 0:59 Structures
  • 2:05 Levels of Structure
  • 4:46 Examples and Functions
  • 5:42 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

Protein molecules are large organic molecules found in living organisms. They serve a wide variety of functions, including structure, transport and defense. Learn more about these molecules in this lesson and take a quiz at the end.

What Is a Protein Molecule?

Protein is a subject that often comes up in conversations about healthy eating. We are told that in order to have a healthy diet, we must eat the proper amounts of protein in addition to carbs and fats. And while we may generally know which foods belong to this group, do we actually know what protein is? Does it only pertain to what we eat? How does it relate to our bodies and other living organisms?

Protein-Rich Foods
Foods with Protein

For starters, protein is a type of molecule that is a part of every living organism. Proteins wear many different hats within an organism, so to speak. For one, protein molecules are structural building blocks within an organism. Protein molecules are also in charge of certain aspects of transport in a body. In addition, they are a crucial part of defense within our immune system. We will discuss these examples in depth a little later.


We have already established that protein is a molecule. More specifically, it is an organic molecule. However, this does not mean organic in the sense of being grown naturally without pesticides. In the scientific world, organic refers to compounds containing carbon. Zooming in at the molecular level, we can see that proteins are made up of carbon, hydrogen, oxygen and nitrogen atoms. These atoms bond together to form molecules. And the molecules fit together to form the subunits of proteins, which are known as amino acids.

Amino acids are the basic building blocks of protein molecules. When they are linked together in a specific order, they make up a particular protein. There are just twenty amino acids in all, but it is the types and sequence of these subunits that make it possible for the enormous variety in protein molecules. Amino acids are joined by what are known as peptide bonds. Therefore, the completed chain is called a polypeptide.

Levels of Structure

There are three levels of structure in these highly sophisticated molecules. The primary level of structure has to do with the number and sequence of amino acids in that particular protein. You can compare this sequencing process to using the alphabet to create words. For example, you can take the letters T-A-C and make the word CAT. However, if you change the sequence, you can make the word ACT. You are still using the same letters, but you have made a different word with a completely different meaning.

Now let's get a visual of this concept from a three-dimensional perspective. Imagine that the twenty amino acids are colored beads. For a particular protein, you must string 100 of these in a very specific order onto a wire. If you vary the order even by one bead, you will be creating an entirely different protein. When you are finished, you now have the primary structure of the protein.

Now on to the secondary level of structure. Once the amino acids are sequenced, the chain is coiled and folded into a specific shape. Imagine our wire with the sequence of beads. Now you will take the wire to coil it in certain spots and fold it in others. You have now created a three-dimensional model of your protein, complete with secondary structure.

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