Structure
Home Table of Contents Preliminary Information Common Amino Acids Structure Functions Proteins for Energy Protein in the Diet Wrap-Up

 

Peptides
Primary Structure
Secondary Structure
Tertiary Structure
Quaternary Structure
Protein Structure

Structure

The way that these twenty amino acids are put together to make proteins determines the structure of the proteins. That structure, in turn, determines the function of the proteins, that is, what role the protein plays in the living thing.

Abbreviations for twenty amino acids. [68020.jpg]

In this section we will look at several aspects of how amino acids are bonded together to make proteins. First, how amino acids bond together by way of peptide bonds (or linkages) to form peptides which can extend in length to create the primary structure of proteins. We will look at how the amino acid chains twist and fold back upon themselves to create the secondary and tertiary structure of proteins. We will look at how some proteins are formed from the interconnection of two or more amino acid chains in what we call quaternary structure. We will finish this section with a look at how all of these facets contribute to the overall protein structure.

Before looking at how amino acids bond to one another, let's make a change in the way that we represent their structure. One common way of representing the amino acid structures is this way. This vertical orientation of the carbon chain emphasizes the stereogenic nature of the alpha carbon (C#2) and shows that the amino group is on the left hand side of the carbon when represented in this way. So we have L-a-amino acids.

Model of amino acid in vertical orientation. [68022.jpg]

 

The functional groups that will be used to bond the amino acids together are the amine group and the carboxylic acid group. For convenience, we can change the orientation to one like this in which we have the amino group on the left side, the carboxylic acid group on the right side, and the side group is down. The molecule is the same but the orientation of the functional groups has been altered to make it easier to show how amino acids bond to one another to make peptides.

Model of amino acid in horizontal orientation. [68024.jpg]

 

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