Textbook Question
Glycine has the zwitterion structure shown. Draw the structure and give the net charge of glycine that will predominate at the indicated pH values (pI = 6.0).
a. pH 1.5
Ch.10 Proteins Workers of the Cell
Frost4th EditionGeneral, Organic and Biological ChemistryISBN: 9780134988696
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Table of contents
- Ch.4 Introduction to Organic Compounds75
- Ch.5 Chemical Reactions19
- Ch.6 Carbohydrates Life's Sweet Molecules62
- Ch.7 States of Matter and Their Attractive Forces8
- Ch.8 Solution Chemistry Sugar and Water Do Mix4
- Ch.10 Proteins Workers of the Cell89
- Ch.11 Nucleic Acids Big Molecules with a Big Role69
- Ch.12 Food as Fuel An Overview of Metabolism65
Frost4th EditionGeneral, Organic and Biological ChemistryISBN: 9780134988696Not the one you use?Change textbook
Chapter 6, Problem 12b
Glycine has the zwitterion structure shown. Draw the structure and give the net charge of glycine that will predominate at the indicated pH values (pI = 6.0).
b. pH 12.0
Verified step by step guidance1
Understand the concept of a zwitterion: A zwitterion is a molecule that has both positive and negative charges but is overall electrically neutral. Glycine, an amino acid, exists as a zwitterion at its isoelectric point (pI), which is pH 6.0 in this case.
At pH values above the pI (e.g., pH 12.0), the environment is basic, meaning there is a low concentration of H⁺ ions. This will affect the protonation state of glycine's functional groups.
Identify the functional groups in glycine: Glycine has an amino group (-NH₃⁺ in its protonated form) and a carboxylic acid group (-COO⁻ in its deprotonated form). At pH 12.0, the amino group will lose a proton, becoming -NH₂, while the carboxylic acid group remains deprotonated as -COO⁻.
Determine the net charge: At pH 12.0, the amino group (-NH₂) is neutral, and the carboxylate group (-COO⁻) carries a negative charge. Therefore, the net charge of glycine at pH 12.0 is -1.
Draw the structure: The structure of glycine at pH 12.0 will have the central carbon atom bonded to a hydrogen atom, a -CH₂ group, a neutral -NH₂ group, and a negatively charged -COO⁻ group. This reflects the deprotonated state of glycine in a basic environment.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Zwitterion Structure
A zwitterion is a molecule that has both positive and negative charges but is overall neutral. In the case of amino acids like glycine, the amino group (-NH3+) carries a positive charge, while the carboxyl group (-COO-) carries a negative charge. This dual charge allows zwitterions to exist in a stable form in solution, particularly at physiological pH levels.
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Isoelectric Point (pI)
The isoelectric point (pI) is the pH at which a molecule, such as an amino acid, carries no net electrical charge. For glycine, the pI is 6.0, meaning that at this pH, the positive and negative charges balance out. Understanding the pI is crucial for predicting the charge of glycine at different pH levels, which influences its solubility and interactions in biological systems.
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pH and Charge Relationship
The pH of a solution affects the ionization state of amino acids. At pH values below the pI, glycine will predominantly exist in its positively charged form, while at pH values above the pI, it will exist in its negatively charged form. At pH 12.0, which is significantly above the pI, glycine will predominantly be negatively charged due to the deprotonation of the amino group.
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Related Practice
Textbook Question
Consider the following tripeptide:
a. Circle the N-terminal amino acid, and give its name. Draw a square around the C-terminal amino acid, and give its name.
Textbook Question
Write the products for the following condensation or hydrolysis reactions:
a.
Textbook Question
Isoleucine has the zwitterion structure shown. Draw the structure and give the net charge of isoleucine that will predominate at the indicated pH values (pI = 6.0).
b. pH 6.0
Textbook Question
Write the products for the following condensation or hydrolysis reactions:
a.
Textbook Question
Draw the structure for the amino acid represented by each of the following abbreviations:
d. Y