Secondary Structure of Protein: Definition & Overview

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  • 0:03 What Is Protein Structure?
  • 1:00 Alpha Helices
  • 1:46 Beta-Pleated Sheets
  • 2:28 DSSP
  • 3:25 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.

There are four levels to protein structure. Primary is encoded in DNA. Secondary involves interactions within the protein. Tertiary and quaternary involve chemical interactions within and without the protein. This lesson describes secondary structure.

What Is Protein Structure?

By definition, the structure of a protein is based on the linear sequence of amino acids (primary structure) combined with how these amino acids interact with each other. These interactions occur within a single protein (secondary and tertiary structure) and between proteins (quaternary structure).

The primary structure of a protein is encoded in your DNA. In order to make a protein, you must first make a copy of the DNA through transcription. This process happens in the nucleus. In the cytoplasm, ribosomes will interact with the transcript and create a protein (polypeptide) from individual amino acids. This process is called translation and produces the primary protein structure. Secondary protein structure is the general 3-dimensional form of local segments of a protein. The most common secondary structures are alpha helices and beta-pleated sheets.

Alpha Helices

Alpha helices are the most common form of secondary structure in proteins. They are created by right-handed coiling of the primary protein structure. The coiling is caused by hydrogen bond interactions between the amino acids within the protein.

Image of Rhodopsin

Alpha helices are often found in DNA binding motifs. These are regulatory proteins that interact with DNA. They are also found in regions of a protein that are able to span a membrane. Because of this, they are often part of membrane-spanning proteins such as pore proteins. They can also act as an anchor for proteins that need to be associated with a membrane but not necessarily embedded within the protein. The image shows rhodopsin. This protein has seven helices arranged up-and-down in a ring (red corkscrew shapes).

Beta-Pleated Sheets

The beta-pleated sheet is the second most common form of secondary structure in a protein. In fact, it is almost as common as the alpha helix. These are called sheets because they consist of strands of amino acids stretched out as much as they can be. Then, these individual strands are packed together to form a sheet. If you think about uncooked Ramen noodles, you're getting the idea of what these look like.

Image of beta sheets

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