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Chapter 4: Problem 28

The structure of the peptide bond is drawn in Section \(4.1\) in the trans configuration in which the carbonyl group and the amino hydrogen are on opposite sides of the peptide bond. Draw the structure of the peptide bond in the cis configuration. Which configuration is more likely to be found in proteins and why?

Short Answer

Expert verified
The trans configuration is more common in proteins because it is more stable and minimizes steric hindrance.

Step by step solution

01

Understand Trans and Cis Configurations

In a peptide bond, the trans configuration occurs when the carbonyl group's oxygen and the amino group's hydrogen are on opposite sides. Conversely, in the cis configuration, these groups are on the same side.
02

Draw the Trans Configuration

The trans configuration of a peptide bond is characterized by the arrangement where the carbonyl oxygen and the amino hydrogen are on opposite sides of the peptide bond plane: \[ \text{N-H} \quad \text{C=O} \]}
03

Draw the Cis Configuration

For the peptide bond in the cis configuration, rearrange the groups such that both the carbonyl oxygen and amino hydrogen are on the same side of the bond: \[ \text{N-H} \quad / \quad \text{C=O} \ \quad \backslash \]
04

Determine the Most Common Configuration in Proteins

Proteins are more likely to have peptide bonds in the trans configuration. This is because the trans configuration is more stable due to less steric clash or hindrance between the side chains of adjacent amino acids.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Trans Configuration
In the world of peptide bonds, the trans configuration is one where the carbonyl oxygen and the amino hydrogen are positioned on opposite sides of the peptide bond. This arrangement is like having the two atoms "turn their backs" on each other. But why is this setup so crucial? Well, nature tends to favor structures that minimize repulsion. The trans configuration helps in reducing any potential conflicts among surrounding atoms or groups. This means that each atom gets enough space, allowing for a stable protein formation.
Cis Configuration
The cis configuration takes a different stance, having both the carbonyl oxygen and the amino hydrogen situated on the same side of the peptide bond. It's akin to the two atoms "facing" each other. While this might sound cozy, it often leads to problems because it reduces the available space for adjacent atoms. In proteins, the cis configuration is unusual due to this potential for more steric clashes. However, certain proteins might still use a cis configuration for specific functional needs, despite the tight squeeze.
Protein Structure
The structure of proteins is a beautifully complex puzzle. Peptide bonds are essential pieces of this puzzle. The way these bonds are arranged, either in trans or cis formations, plays a pivotal role in defining the protein's shape and functionality. Proteins predominantly favor the trans configuration, as it supports more expansive and intricate structures. This setup facilitates the formation of long chains without the jostling caused by adjacent amino acids trying to elbow into the same space. Thus, a stable protein structure is primarily built upon trans-configured peptide bonds.
Steric Hindrance
Steric hindrance is all about space. In a molecular world, it's the interference experienced by atoms or groups when they are too close to one another. Within peptide bonds, steric hindrance is a key factor in determining whether a trans or cis configuration is more stable. Trans configurations generally minimize such clashing, making them more favorable, as the atoms are more comfortably spaced apart. In the crowded realm of the cis configuration, steric hindrance increases, leading to instability. Understanding steric hindrance is crucial for grasping why certain configurations predominate in nature's protein structures.

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Most popular questions from this chapter

In 1957, Christian Anfinsen carried out a denaturation experiment with ribonuclease (a pancreatic enzyme that catalyzes the digestion of RNA), which consists of a single chain of 124 amino acids cross-linked by four disulfide bonds. Urea and 2 -mercaptoethanol were added to a solution of ribonuclease, which caused it to unfold, or denature. The loss of tertiary structure resulted in a loss of biological activity. When the denaturing agent (urea) and the reducing agent (mercaptoethanol) were simultaneously removed, the ribonuclease spontaneously folded back up to its native conformation and regained full enzymatic activity in a process called renaturation. What is the significance of this experiment?

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