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.
Ch.18 Amino Acids and Proteins
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 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
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook
Chapter 18, Problem 7
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?
Verified step by step guidance1
Step 1: Understand the structure of an amino acid. Each amino acid consists of a central carbon atom (called the alpha carbon) bonded to four groups: an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and a unique side chain (R group) that determines the properties of the amino acid.
Step 2: Draw the structure of valine. The side chain (R group) of valine is an isopropyl group (-CH(CH₃)₂), which consists only of carbon and hydrogen atoms. These atoms share electrons almost equally, making the side chain nonpolar and hydrophobic.
Step 3: Draw the structure of serine. The side chain (R group) of serine is a hydroxymethyl group (-CH₂OH), which contains an -OH group. The oxygen atom in the -OH group is highly electronegative, creating a polar bond due to the unequal sharing of electrons between oxygen and hydrogen.
Step 4: Explain why valine's side chain is nonpolar. The isopropyl group in valine's side chain lacks electronegative atoms like oxygen or nitrogen, so it does not form significant dipoles. This makes the side chain nonpolar and hydrophobic, meaning it does not interact well with water.
Step 5: Explain why serine's side chain is polar. The hydroxyl (-OH) group in serine's side chain creates a dipole due to the electronegativity difference between oxygen and hydrogen. This makes the side chain polar and hydrophilic, meaning it can form hydrogen bonds and interact well with water.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
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). The nature of the side chain determines the amino acid's properties, such as polarity and hydrophobicity.
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Polarity of Side Chains
The polarity of an amino acid's side chain is determined by the presence of functional groups that can form hydrogen bonds with water. Nonpolar side chains, like that of valine, consist mainly of hydrocarbons, making them hydrophobic and less likely to interact with water. In contrast, polar side chains, such as that of serine, contain hydroxyl (-OH) or other polar groups, allowing them to interact favorably with water.
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Hydrophobic and Hydrophilic Interactions
Hydrophobic interactions occur when nonpolar molecules or regions of molecules aggregate to avoid contact with water, while hydrophilic interactions involve polar molecules that readily interact with water. These interactions are crucial in determining the structure and function of proteins, influencing how amino acids with different side chains behave in aqueous environments.
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Related Practice
Textbook Question
Examine the ball-and-stick model of valine below. Identify the carboxyl group, the amino group, and the R group.
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Textbook Question
Is serine chiral? Draw serine and identify the chiral atom. Explain why serine is chiral.
Textbook Question
Indicate whether each of the following molecules is an α-amino acid or not, and explain why.
a.
Textbook Question
Which amino acid is hydrophilic (dissolves in aqueous solutions)? Why?
a. isoleucine
b. phenylalanine
c. aspartic acid
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.