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Ch.16 Amino Acids, Proteins, and Enzymes
Timberlake - Chemistry: An Introduction to General, Organic, and Biological Chemistry 13th Edition
Timberlake13th EditionChemistry: An Introduction to General, Organic, and Biological ChemistryISBN: 9780134421353Not the one you use?Change textbook
All textbooksTimberlake 13th EditionCh.16 Amino Acids, Proteins, and EnzymesProblem 59c
Chapter 16, Problem 59c

Identify the amino acids and type of interaction that occurs between the following R groups in tertiary protein structures:
c. —CH2—SH and HS—CH2—

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1
Identify the amino acids that contain the R group —CH₂—SH. This functional group is characteristic of the amino acid cysteine, which has a thiol (-SH) group in its side chain.
Recognize that the interaction between two cysteine residues occurs through their thiol (-SH) groups. These groups can undergo an oxidation reaction to form a disulfide bond (-S—S-).
Understand that disulfide bonds are a type of covalent bond and are important in stabilizing the tertiary structure of proteins by linking different parts of the polypeptide chain.
Write the chemical reaction for the formation of a disulfide bond: R-SH+R-SH→R-S-S-R+H2O.
Conclude that the interaction between the two R groups —CH₂—SH and HS—CH₂— is a disulfide bond, which is a covalent interaction that contributes to the stabilization of the protein's tertiary structure.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Amino Acids

Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid has a central carbon atom, an amino group, a carboxyl group, a hydrogen atom, and a distinctive R group (side chain) that determines its properties. The specific R groups of amino acids influence how they interact with each other, which is crucial for protein structure and function.
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Tertiary Protein Structure

Tertiary protein structure refers to the three-dimensional shape of a protein that results from the folding and interactions of its polypeptide chains. This structure is stabilized by various interactions among the R groups of amino acids, including hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges. Understanding tertiary structure is essential for grasping how proteins function in biological systems.
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Disulfide Bonds

Disulfide bonds are covalent linkages formed between the sulfur atoms of two cysteine amino acids, which can significantly stabilize the tertiary structure of proteins. In the context of the given R groups (—CH₂—SH and HS—CH₂—), these groups can form a disulfide bond when they come into proximity, contributing to the overall stability and functionality of the protein. This type of interaction is particularly important in extracellular proteins that require a stable structure.
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Related Practice
Textbook Question

Fresh pineapple contains the enzyme bromelain that hydrolyzes peptide bonds in proteins.

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a. The directions for a gelatin (protein) dessert say not to add fresh pineapple. However, canned pineapple where pineapple is heated to high temperatures can be added. Why?

Textbook Question

Fresh pineapple contains the enzyme bromelain that hydrolyzes peptide bonds in proteins.

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b. Fresh pineapple is used in a marinade to tenderize tough meat. Why?

Textbook Question

Identify the amino acids and type of interaction that occurs between the following R groups in tertiary protein structures:

a.

Textbook Question

What type of interaction would you expect between the following in a tertiary structure?

a. threonine and glutamine

Textbook Question

Draw the condensed structural formula for Ser–Lys–Asp.

Textbook Question

Would you expect to find this segment at the center or at the surface of a protein? Why?