Tertiary Structure of Protein: Definition & Overview

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  • 0:01 Definition of Tertiary…
  • 0:54 Disulfide Bonds
  • 1:15 Hydrogen Bonding
  • 2:03 Ionic Bonds
  • 2:22 Non-Polar Hydrophobic…
  • 3:11 Lesson Summary
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Lesson Transcript
Instructor: Shannon Compton

Shannon teaches Microbiology and has a Master's and a PhD in Biomedical Science. She also researches cancer and neurodegenerative diseases.

Tertiary protein structure turns a simple polypeptide with pretty little ribbons and twists into a big, globular mass. Amino acid side chains are the culprit. Read this lesson to find out why.

Definition of Tertiary Structure

Tertiary protein structure is one step more complicated than secondary structure. Recall that secondary structures are made of alpha helices and beta-pleated sheets. These are both local structures. Tertiary structures involve packaging the secondary structures into compact globular regions called protein domains.

A protein can have one or more domains. The important factor for tertiary structure is that it contains only one polypeptide. If more than one is involved then it becomes quaternary structure. Tertiary protein domains are formed by combinations of disulfide bonds, hydrogen bonds, ionic bonds, and non-polar hydrophobic interactions. The type of side chain on the amino acid determines the type of interaction.

Disulfide Bonds

Disulfide bonds are formed by oxidation of the sulfhydryl groups on the amino acid cysteine. These are also referred to as disulfide bridges, so think of them that way: as a connecting bridge. Different protein chains, or loops within a single chain, are held together by strong covalent disulfide bonds.

Hydrogen Bonding

Hydrogen bonding between amino acid side chains happens frequently. Most often they form between two alcohols, an alcohol and an acid, two acids, or an alcohol and an amine or amide. The following are examples of amino acid side chains that form hydrogen bonds. The alcohols ser, thr, and tyr can form bonds to each other. The alcohol asp and the acid tyr can form a bond.

The acids asp and glu can bond through their hydrogens. An example of an alcohol and amine that hydrogen can bond are ser and lys. Finally, the alcohol ser and the amide asn can form hydrogen bonds (labeled as a hydrogen bond).

Ionic Bonds

Ionic bonds (also called salt bridges) form between an acidic amino acid and an amine when each is neutralized. The ionic bond forms between the positively charged ammonium group and the negatively charged acid group. Any combination of the various acidic or amine amino acid side chains can do this.

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