The Biology Project: Biochemistry

Large Molecules Problem Set

Problem 5: Elements of protein structure

Tutorial to help answer the question

Which statement is true concerning the structure of proteins?


Here is a review of features of protein structure that can be used to analyze the different answer choices. You may discover that all of the answer choices are correct!

Protein structures
Primary structure
Proteins are composed of 20 different kinds of amino acids joined in a linear polypeptide chain by peptide bonds. The primary structure is the sequence of the amino acids.

Secondary structure
Protein secondary structure refers to regular, repeated patters of folding of the protein backbone. The two most common folding patterns are the alpha helix and the beta sheet.

Tertiary structure
Tertiary structure refers to the overall folding of the entire polypeptide chain into a specific 3D shape.

Quaternary structure
The quaternary structure describes the way in which the different subunits are packed together to form the overall structure of the protein. Proteins made of two or more polypeptide chains have quaternary structure.

(For more information on structures, refer to the tutorial for problem 3)

Amino Acid Side Chains (R-groups)

There are 20 different amino acids found in proteins. The side chains (R-groups) differ in chemical properties. Some are polar, but uncharged. Some are polar and normally have a positive or negative charge in solution.

Amino acids with polar side chains are said to be hydrophilic (water loving) because they form weak interactions with water molecules. The R-groups of hydrophilic amino acids contain electronegative atoms like O and N. Some amino acids are non-polar (hydrophobic) because their side chains are made up mostly of hydrocarbon chains.

Examples of different categories of amino acids:
Structural formula for isoleucine (hydrophobic) structural formula for asparagine (hydrophillic-uncharged) structural formula for glutamic acid (hydrophilic-charged)
molecular formula for isoleucine (hydrophobic) molecular formula for asparagine (hydrophillic-uncharged) molecular formula for glutamic acid (hydrophilic-charged)
Different proteins have different structures and properties due to the specific locations of hydrophilic and hydrophobic amino acids.

Problem 5 Answer problem 6

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