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Structure and Function of the Alpha Helix

Amanda Robb, Stephanie Gorski, Elaine Chan
  • Author
    Amanda Robb

    Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.

  • Instructor
    Stephanie Gorski

    Steph has a PhD in Entomology and teaches college biology and ecology.

  • Expert Contributor
    Elaine Chan

    Dr. Chan has taught computer and college level physics, chemistry, and math for over eight years. Dr. Chan has a Ph.D. in Chemistry from U. C. Berkeley, an M.S. Physics plus 19 graduate Applied Math credits from UW, and an A.B. with honors from U.C .Berkeley in Physics.

Learn about the alpha helix. Discover the alpha helix structure and beta sheet hydrogen bonds, and examine alpha helix proteins and amino acids. Updated: 03/08/2022

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What is an Alpha Helix?

An alpha helix is a secondary structure in proteins where the polypeptide chain is curved like a spiral. Proteins are an important part of living things. Inside cells, proteins make up enzymes, which catalyze chemical reactions. They also form structures, transport materials and help with cell motility, cell division, and more. Proteins are able to do a diverse array of jobs inside the cell due to their unique three-dimensional structure. The structure of a protein is determined by its amino acid sequence. Proteins are made of long strands of amino acids called polypeptide chains. The way the polypeptide chains folds and allows amino acids to interact with each other creates the three-dimensional structure necessary for their function.

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  • 0:04 The Alpha Helix & Structures
  • 1:11 Amino Acid Structure
  • 2:02 The Alpha Helix Structure
  • 2:59 Why Alpha Helix?
  • 3:59 Are Alpha Helices Permanent?
  • 4:47 Lesson Summary
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Alpha Helix and Beta Sheet

The primary structure of a protein is the amino acid sequence of the polypeptide chain. The way the polypeptide chain forms hydrogen bonds determines the secondary structure. There are two main types of secondary structures in proteins, alpha helices and beta pleated sheets. The hydrogen bonding pattern of the amino acids in the polypeptide chain determine whether an alpha helix or a beta pleated sheet will form. Polypeptide chains can have alpha helices, beta pleated sheets or both. Alpha helices are formed like a right handed spiral, whereas beta pleated sheets look like accordion folds.

Why Alpha Helix Hydrogen Bonds?

Alpha helices make more efficient use of hydrogen bonding availability compared to beta pleated sheets and thus are more compressed. Alpha helices are also the most common secondary structure in proteins.

To understand how alpha helices are formed, first the structure of amino acids must be understood. Amino acids are made of a central carbon atom bonded to a carbonyl group on one side, an amino group on the opposite side, a hydrogen atom and a side chain that is variable. In alpha helices the carbonyl group hydrogen bonds to the amino group of the amino acid that is four away from it. This creates a tight spiral pattern that forms the alpha helix. The side chains of the amino acids extend outward from the helix, allowing them to interact and help produce further structures in the protein.


The structure of an alpha helix

alpha helix


Secondary structure is important. If a protein that is supposed to have alpha helices misfolds into beta pleated sheets, diseases can occur. For example, prion diseases are protein folding disorders where a protein with alpha helices is converted to having beta pleated sheets. This misfolded protein can then turn neighboring proteins into misfolded proteins as well. These proteins are not able to do their job and can cause problems. Prion diseases, like mad cow disease or Creutzfeldt-Jakob disease are caused by misfolded prion proteins where alpha helices have turned into beta pleated sheets.

Alpha Helix Structure

The alpha helix secondary structure is one of four layers of structure in proteins. The levels of protein structure include:

  • Primary
  • Secondary
  • Tertiary
  • Quaternary

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  • Activities
  • FAQs

Alpha Helix Protein Questions


Quaternary Structure

Hemoglobin (more than 70% alpha helix) has four regions where the oxygen binds and releases. The hemoglobin shape changes with the oxygen phases. The shape of protein also changes slightly due to individual differences.

1.The shape of hemoglobin is what kind of structure? (a) primary (b) secondary (c) tertiary (d) quaternary

Tertiary Structure

2.The three dimensional shape of the protein is determined mainly by what?

(a) sequence of amino acids (b) presence of alanine (c) absence of glycine (d) random amino acids

Secondary Structure

3.The main kinds of secondary structure are?

(a) alpha helices and beta sheets (b) random coils (c) denatured proteins (d) beta sheets

4.Amino acids that are not likely to form an alpha helix are?

(a) proline and glycine (b) alanine (c) leucine

5.A helix propensity scale, based on experimental evidence of the frequency of certain amino acids in alpha helices, finds that the three highest amino acids are?

(a) alanine, leucine, arginine

(b) alanine, tyrosine, valine

(c) glycine, alanine, histidine

Primary Structure

6.The COOH from one amino acid and the NHH of another amino acid form what?

(a) peptide bond (b) H bond (c) resonance

In this section of the carbon backbone of the amino acid chain, -N-C-C-N-C-C- , the first C on the left and the second C from the right have residues (side-chains) attached to them.

7.The carbon atom with the residue is called what?

(a) C-alpha (b) C-beta (c) carbon backbone

These residues are twenty different side-chains that distinguish one amino acid from another. These side chains can rotate about the C(alpha)-C bond and have many conformations.

8.The different rotational positions of the residues are called what?

(a) rotamers (b) isotopes (c) variations (d) translations

The bonds between the C(alpha) and N and C(alpha) and C can rotate. These angles are found experimentally to be restricted to certain values for alpha helices and certain values for beta sheets.

9.This is represented graphically as?

(a) Ramachandran Plot (b) Plotkin Plot (c) Ambrose Plot

Answers:

1. (d) and (c) 2. (a) 3. (a) 4. (a) 5. (a) 6. (a) 7. (a) 8. (a) 9. (a)

What is alpha helix structure?

An alpha helix structure is a type of secondary structure in a protein. In an alpha helix the polypeptide chain twists like a spiral via hydrogen bonding between the amino acids.

How is an alpha helix held together?

An alpha helix is held together with hydrogen bonds. These bonds form between the amino group of one amino acid and the carbonyl group of another located about 4 amino acids away. This forms a twisted, helical structure.

Which amino acids are found in alpha helix?

The amino acids that have a high probability of being found in an alpha helix are methionine, alanine, leucine, glutamate, and lysine. These amino acids often form an alpha helix due to the structure of their side chains.

What level of protein structure is alpha helix?

An alpha helix is a secondary level of protein structure. Proteins have four possible levels of structure. The primary structure is the amino acid sequence, the secondary structure is created by hydrogen bonding, the tertiary structure is the overall three dimensional shape of the protein and the tertiary structure is any subunits that are part of the protein.

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