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Globular Proteins: Definition, Structure & Examples

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  • 0:01 What Are Globular Proteins?
  • 0:34 Structure
  • 2:33 Examples
  • 4:05 Lesson Summary
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Lesson Transcript
Instructor: Leigh Carman

Leigh Ann holds a master's degree in science and has taught middle and high school science for over ten years.

Explore what makes globular proteins different from other groups of proteins. Learn about the definition and structure of globular proteins as well as some examples and their functions.

What Are Globular Proteins?

Did you enjoy your scrambled eggs this morning? Or, perhaps you prefer your eggs fried sunny-side up or folded with ham and cheese into a delicious omelet. Eggs, specifically egg whites, contain a type of protein called albumin, or ovalbumin. Ovalbumin is an example of a globular protein, one that is water-soluble and shaped roughly like a globe or a sphere when coiled up into its functional form. Let's explore more about globular proteins and their structure.

Structure

Based on solubility, function, and three-dimensional shape, proteins may be classified as fibrous, membrane, or globular. Globular proteins, like ovalbumin, are always soluble in water and often have a spherical or roundish shape.

As in all proteins, the primary structure of globular proteins consists of a polypeptide, or chain of amino acids joined via peptide bonds. Hydrogen bonds between carboxyl and amine groups of the amino acids contribute to the secondary structure, which in globular proteins may include alpha-helices, beta-sheets, or both. Globular proteins are folded such that their tertiary structure consists of the polar, or hydrophilic, amino acids arranged on the outside and the nonpolar, or hydrophobic, amino acids on the inside of the three-dimensional shape. This arrangement is responsible for the solubility of globular proteins in water.

Some globular proteins, such as hemoglobin, also exhibit quaternary structure, in which multiple polypeptide chains are clustered together to form a functional protein. The shape of globular proteins is critical to their function. Those acting as enzymes, for example, must be folded such that their active sites are in the correct orientation and conformation to interact with their substrates.

Changes in environmental conditions, such as pH or temperature, may affect the bonds that contribute to the shape of globular proteins. These changes can lead to denaturation in which the shape of the protein is so altered that it is no longer functional. In the case of your eggs at breakfast, the heat used in cooking the eggs denatures the ovalbumin and other proteins in the egg whites, causing them to unfold and clump together into a yummy conglomeration of goodness.

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