Factors Affecting Protein Structure

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  • 0:05 Protein Shape
  • 1:09 Forces Affecting Structure
  • 2:50 Denaturation
  • 4:56 Lesson Summary
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Lesson Transcript
Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, learn the basics of protein structure and four factors that contribute to protein structure. Also, learn how this structure can be denatured and what that does to the protein.

Protein Shape

Did you know that if the proteins in your body change shape even slightly, then your entire body can end up in chaos? For example if hemoglobin were to simply change the distance between two amino acids, then oxygen would not fit in the space as snugly. Therefore, the oxygen wouldn't be bound in the lungs as well, so our blood would not receive the oxygen that it needs. All that it takes is two amino acids to shift slightly and we won't be able to use the oxygen. It's a good thing that our body uses several factors to ensure the proteins can't shift shape, and proteins themselves utilize several factors to help keep their shape.

First, a little background: proteins have several 'levels' of structure. There are primary, secondary, and tertiary levels. Primary structure is simply the amino acid sequence, secondary is the 3-D conformation that a section of that sequence will hold, and tertiary is how all sections of a protein interact. When referring to individual amino acids in a protein, we will sometimes refer to them as 'residues.'

Forces Affecting Structure

The main forces that affect structure are electrostatic forces, hydrogen bonding forces, hydrophobic forces, and disulfide bonds. Each of these affect protein structure in different ways.

The electrostatic forces are when two like charges are repelled or two opposite charges are attracted. These forces are not very strong, but they can drastically alter the way the protein will fold.

Hydrogen bonding drives two of the most common protein structures, alpha helix and beta sheets. An alpha helix is a right-handed spiral. Hydrogen bonds, with the hydrogen from NH and the oxygen from the OH on each amino acid backbone, form at every 3-4 amino acid residues (individual amino acids). This means that each spiral is 3.6 angstroms long. A beta sheet has a straight chain that will then bend back on itself like a ribbon. Each corresponding sheet will be connected with 2-3 hydrogen bonds, once again between the NH and OH on the amino acid residues.

Hydrophobic forces will produce some of the most drastic changes in protein structure. Hydrophobic means 'water fearing.' There are some amino acid residues that are not able to be in water, while others love being in water. Since our body is water-based, proteins will fold so that all of the hydrophobic residues are on the inside of the water, protected from the water by the amino acids residues that like being in water.

Disulfide bonds are the strongest forces affecting protein structure. An actual covalent bond can form between the sulfurs on two cysteine amino acids. Since an actual covalent bond is formed, it creates a very rigid structure that is not able to move very much.

Denaturation

Since proteins are only able to function properly in their specific shape, they will typically stay in that configuration unless something forces them to change. When proteins change their shape, this is called denaturation. Some external forces that affect protein shape are pH and temperature.

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