Textbook Question
Indicate whether each of the following molecules is an α-amino acid or not, and explain why.
a.
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Ch.18 Amino Acids and Proteins
McMurry8th EditionFundamentals of GOBISBN: 9780134015187
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Table of contents
- Ch.1 Matter and Measurements27
- Ch.2 Atoms and the Periodic Table20
- Ch.3 Ionic Compounds8
- Ch.4 Molecular Compounds23
- Ch.5 Classification & Balancing of Chemical Reactions12
- Ch.6 Chemical Reactions: Mole and Mass Relationships28
- Ch.7 Chemical Reactions: Energy, Rate and Equilibrium64
- Ch.8 Gases, Liquids and Solids24
- Ch.9 Solutions52
- Ch.10 Acids and Bases25
- Ch.11 Nuclear Chemistry22
- Ch.12 Introduction to Organic Chemistry: Alkanes57
- Ch.13 Alkenes, Alkynes, and Aromatic Compounds47
- Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen50
- Ch.15 Aldehydes and Ketones45
- Ch.16 Amines42
- Ch.17 Carboxylic Acids and Their Derivatives57
- Ch.18 Amino Acids and Proteins82
- Ch.19 Enzymes and Vitamins63
- Ch.20 Carbohydrates44
- Ch.21 The Generation of Biochemical Energy65
- Ch.22 Carbohydrate Metabolism45
- Ch.23 Lipids42
- Ch.24 Lipid Metabolism33
- Ch.25 Protein and Amino Acid Metabolism24
- Ch.26 Nucleic Acids and Protein Synthesis45
Chapter 18, Problem 8
Which amino acid is hydrophilic (dissolves in aqueous solutions)? Why?
a. isoleucine
b. phenylalanine
c. aspartic acid
Verified step by step guidance1
Identify the chemical properties of each amino acid listed in the options. Amino acids can be classified as hydrophilic (water-loving) or hydrophobic (water-fearing) based on the nature of their side chains (R groups).
Examine isoleucine: Isoleucine has a nonpolar, aliphatic side chain. Nonpolar side chains are hydrophobic because they do not interact well with water molecules.
Examine phenylalanine: Phenylalanine has a nonpolar, aromatic side chain. Aromatic side chains are generally hydrophobic because they lack polar groups that can form hydrogen bonds with water.
Examine aspartic acid: Aspartic acid has a polar, negatively charged side chain due to the presence of a carboxylate group (-COO⁻). Charged and polar side chains are hydrophilic because they can form hydrogen bonds and interact with water molecules.
Conclude that aspartic acid is hydrophilic because its negatively charged side chain allows it to dissolve in aqueous solutions, while isoleucine and phenylalanine are hydrophobic due to their nonpolar side chains.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hydrophilicity
Hydrophilicity refers to the property of a molecule that allows it to interact favorably with water. Hydrophilic substances tend to be polar or charged, enabling them to form hydrogen bonds with water molecules, which facilitates their dissolution in aqueous solutions. This property is crucial in biological systems, as it influences the solubility and transport of molecules within cells.
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Amino Acid Structure
Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid consists of a central carbon atom, an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group) that determines its properties. The nature of the side chain influences whether the amino acid is hydrophilic or hydrophobic, impacting protein structure and function.
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Polar vs. Nonpolar Side Chains
Amino acids can be classified based on the characteristics of their side chains as polar (hydrophilic) or nonpolar (hydrophobic). Polar side chains contain functional groups that can form hydrogen bonds with water, making them soluble in aqueous environments. In contrast, nonpolar side chains are hydrophobic and tend to aggregate away from water, which is essential for the folding and stability of proteins.
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Related Practice
Textbook Question
Using Table 18.3, name the α-amino acids that (a) contain an aromatic ring, (b) contain sulfur, (c) are alcohols, and (d) have alkyl-group side chains.
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Textbook Question
Valine is an amino acid with a nonpolar side chain and serine is one with a polar side chain. Draw the two amino acids.
a. Why is the side chain for valine nonpolar, whereas the side chain for serine is polar?
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Textbook Question
Is serine chiral? Draw serine and identify the chiral atom. Explain why serine is chiral.
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Textbook Question
Two of the 20 common amino acids have two chiral carbon atoms in their structures. Identify these amino acids and their chiral carbon atoms.
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Textbook Question
Draw the structure of glutamic acid at low pH, at high pH, and at the two forms that exist between low pH and high pH. Which of these structures represents the zwitterion?
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