/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 18 Draw the structure of valine at ... [FREE SOLUTION] | 91影视

91影视

Log out

Learning Materials

Features

Discover

Chapter 21: Problem 18

Draw the structure of valine at \(\mathrm{pH} 1\) and at pH 12

Short Answer

Expert verified
At pH 1, valine has an \(\text{-NH}_3^+\) group and a \(\text{-COOH}\) group. At pH 12, it has an \(\text{-NH}_2\) group and a \(\text{-COO}^-\) group.

Step by step solution

01

Understanding Valine Structure

Valine is an amino acid with the chemical formula C5H11NO2. It contains a central \(\alpha\)-carbon bonded to a carboxyl group (-COOH), an amino group (-NH2), a hydrogen atom, and an isopropyl side chain (-(CH3)2CH). Before we consider the pH, we visualize valine with a neutral charge.
02

Structure of Valine at pH 1

At \(\mathrm{pH} 1\), the environment is very acidic, leading to protonation of groups. The amino group (-NH2) becomes \(\text{-NH}_3^+\), and the carboxyl group remains in its unionized form (-COOH) because it will not deprotonate in such an acidic environment. Therefore, valine at pH 1 looks like this: ! Valine at pH 1 Structure Description !
03

Structure of Valine at pH 12

At \(\mathrm{pH} 12\), the environment is very basic, which results in the deprotonation of groups. The carboxyl group (-COOH) loses a proton to become \(\text{-COO}^-\), while the amino group remains as (-NH2) due to the high \(\text{p}K_a\) of the ammonium ion. Hence, at pH 12, valine takes the following form: ! Valine at pH 12 Structure Description !
04

Drawing Valine Structures

To visualize both structures:- **Valine at pH 1:** Draw the amino group as \(\text{-NH}_3^+\), the carboxyl group as \(\text{-COOH}\) and the isopropyl group remains unchanged.- **Valine at pH 12:** Draw the amino group as \(\text{-NH}_2\), the carboxyl group as \(\text{-COO}^-\), and the isopropyl group unchanged.These are representative structures based on their environment.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

Key Concepts

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

Amino Acid
Amino acids are the building blocks of proteins. Each amino acid has a basic structure consisting of:
  • An amino group (-NH2)
  • A carboxyl group (-COOH)
  • An alpha (\(\alpha\)) carbon
  • A unique side chain, called the R group
In the case of valine, its R group is an isopropyl group (-(CH3)2CH).

Valine has the chemical formula \(\text{C}_5\text{H}_{11}\text{NO}_2\). As an amino acid, valine plays a pivotal role in protein synthesis and various metabolic pathways. Its structure dictates how it behaves under different conditions, such as changes in pH.
pH Effects
The pH level of a solution has significant effects on amino acids and their ionization states. pH is a scale that measures the acidity or basicity of a solution:
  • A pH less than 7 indicates an acidic environment.
  • A pH of exactly 7 is neutral.
  • A pH greater than 7 indicates a basic or alkaline environment.
Valine, like other amino acids, can exist in different ionic forms depending on the pH. At extreme pH values:
  • In acidic conditions (low pH), amino acids tend to gain protons.
  • In basic conditions (high pH), they tend to lose protons.
The behavior of amino acids at different pH levels is crucial, especially in biochemical processes such as enzyme activity and protein folding.
Protonation
Protonation refers to the addition of a proton (H+) to an atom, molecule, or ion. In the context of amino acids, protonation affects the functional groups:
  • The amino group (-NH2) becomes protonated to form \(\text{-NH}_3^+\).
  • The carboxyl group (-COOH) remains unchanged in highly acidic solutions.
At pH 1, valine is in a highly acidic environment:
  • The amino group accepts an additional proton, resulting in its protonated form \(\text{-NH}_3^+\).
  • The carboxyl group does not undergo deprotonation under these conditions and stays as \(\text{-COOH}\).
Understanding protonation helps us predict how amino acids like valine will change in structure at varying pH levels.
Deprotonation
Deprotonation is the opposite of protonation. It involves the removal of a proton (H+) from an atom, molecule, or ion. In amino acids, the carboxyl group is primarily affected:
  • The carboxyl group (-COOH) deprotonates to form \(\text{-COO}^-\).
  • The amino group may remain unchanged in basic environments if its \(\text{p}K_a\) is high.
At pH 12, valine experiences a highly basic environment:
  • The carboxyl group loses a proton, resulting in the deprotonated form \(\text{-COO}^-\).
  • The amino group remains in its neutral form as \(\text{-NH}_2\).
Understanding the deprotonation process is crucial for predicting the structural changes of amino acids in different pH environments.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Based on your knowledge of the chemical properties of amino acid side chains, suggest a substitution for leucine in the primary structure of a protein that would probably not change the character of the protein very much.

The cytochrome \(c\) protein is important in producing energy from food. It contains a heme surrounded by a polypeptide chain. What kind of structure do these two entities form? To which group of proteins does cytochrome \(c\) belong?

What is the effect of salt bridges on the tertiary structure of proteins?

The members of which class of proteins are insoluble in water and can serve as structural materials?

In collagen, some of the chains of the triple helices in tropocollagen are cross-linked by covalent bonds between two lysine residues. What kind of structure is formed by these cross-links? Explain.
See all solutions

Recommended explanations on Chemistry Textbooks

Physical Chemistry

Read Explanation

Chemistry Branches

Read Explanation

Chemical Analysis

Read Explanation

Nuclear Chemistry

Read Explanation

Inorganic Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.