Denaturation of Protein: Definition & Causes

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  • 0:01 What is Protein Denaturation?
  • 1:10 Primary Structure
  • 2:05 Secondary Structure
  • 2:55 Tertiary & Quaternary…
  • 3:22 How Proteins Are Denatured
  • 4:52 Lesson Summary
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Lesson Transcript
Instructor
Derrick Arrington

Derrick has taught biology and chemistry at both the high school and college level. He has a master's degree in science education.

Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

Proteins are found in all living organisms. Problems occur when proteins become denatured. In this lesson, you will learn about a change in proteins known as denaturation.

What Is Protein Denaturation?

Living organisms require many types of large molecules in order to survive. Very few of these molecules serve as many purposes as proteins. Proteins are large molecules composed of folded chains of amino acids. Every protein has a unique shape and that shape determines the things it does. You could think of them as keys that fit into certain locks around the body.

Proteins do lots of different things around the body, including speeding up biological processes, recognizing antibodies, providing structure to certain body parts, transporting substances, regulating genes, and responding to signals inside and outside the body.

Proteins range in size from small ones, such as insulin - only 51 amino acids long, to extremely large ones, such as titin - almost 27,000 amino acids long. No matter their size, they must be folded into a particular shape in order to function. Sometimes, though, things go wrong and cause the protein to unfold. Denaturation is the process by which proteins lose their folded structure and cease to function.

The Structure of Proteins: Primary Structure

Before we tackle denaturation, let's look closer at the structure of proteins. Every protein has four levels of structure which scientists refer to. The four levels are primary, secondary, tertiary, and quaternary.

The primary structure of a protein is the sequence of amino acids that form that protein. Every protein has a unique sequence of amino acids linked together in a long chain. If the amino acids are out of order, the protein will not function properly.

For example, insulin has a chain which begins with the amino acid glycine, followed by isoleucine, valine, and glutamic acid. The chain continues, but you get the idea. If any members of this chain are out of order - for example, if the glycine was switched with the valine, then the resulting chain wouldn't combine to insulin. It's only because the amino acids are linked this way that insulin is created.

The Structure of Proteins: Secondary Structure

The secondary structure of a protein refers to regular repeated patterns in the folding of amino acid chains. Remember, these long chains fold into specific shapes depending on the protein; secondary structure identifies patterns in these folds. There are two types of folding at this level: alpha helixes and beta sheets.

An alpha helix is a spiral coil shape formed by hydrogen bonds between amino acids of the same chain. These bonds cause the chain to curve back around in this spiral pattern.

An image of a protein.

Beta sheets are formed when two amino acid chains align, and the acids of these two chains form hydrogen bonds with one another. These bonds cause the two chains to run parallel to each other and form a flat or wrinkled pattern.

An image of a protein.

The Structure of Proteins: Tertiary and Quaternary Structures

The tertiary structure of a protein describes the specific geometric shape of that protein, or the structure which results from all the alpha helixes and beta sheets of its amino acid chains.

Many proteins are constructed from two folded amino acid chain subunits that come together to form one final protein. The quaternary structure describes the way the position of these amino acid chain subunits relate to each other.

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Additional Activities

Denaturation in Action

Denaturation of proteins causes the protein structure to degrade and subsequently the protein loses its shape. As you read in the lesson, an egg is a great model for protein denaturation because the white is composed mostly of the protein albumin. In this activity, we're going to examine how different conditions affect albumin protein and if they are able to denature it.

Steps

  1. To start, get four bowls. Break one egg into the first bowl, separating the white from the yolk. Discard the yolk but keep the white.
  2. Now, separate the white into four equal parts and put one part into each of the bowls.
  3. In bowl 1, put nothing on the egg white. This is your control.
  4. For bowl 2, make ice cold water with a few ice cubes and cold tap water. Place it in the freezer for 10 minutes, then put 1 cup of ice cold water over the egg white in bowl 2.
  5. For bowl 3, boil water in a kettle or in the microwave. When the water is boiling put 1 cup of boiling water over the egg white in bowl 3.
  6. In bowl 4, add 1 cup of vinegar to the egg white.
  7. Now, wait about 30 minutes and record your results in the table below.

Bowl NumberConditionResult
1
2
3
4

Anaylsis

  1. Which egg whites were denatured by the condition you applied and how did you know?
  2. What types of conditions are able to denature proteins?
  3. Why do you think you got the results you did for bowl 2?
  4. Why is it important to have bowl 1, the control in this experiment?

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