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Questions and Answers
Which of the following is a characteristic of polar amino acids?
Which of the following is a characteristic of polar amino acids?
What is the purpose of disulfide bonds in many extracellular proteins?
What is the purpose of disulfide bonds in many extracellular proteins?
Which of the following is a characteristic of nonpolar (hydrophobic) amino acid side chains?
Which of the following is a characteristic of nonpolar (hydrophobic) amino acid side chains?
What is the significance of the asymmetric carbon atom in amino acids?
What is the significance of the asymmetric carbon atom in amino acids?
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Which of the following is the correct way to represent the formation of a peptide bond between two amino acids?
Which of the following is the correct way to represent the formation of a peptide bond between two amino acids?
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What is the defining characteristic of alpha-amino acids?
What is the defining characteristic of alpha-amino acids?
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Which of the following amino acids has a nonpolar, aliphatic side chain?
Which of the following amino acids has a nonpolar, aliphatic side chain?
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Which amino acid is classified as both nonessential and conditional?
Which amino acid is classified as both nonessential and conditional?
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What is the primary covalent bond that links amino acids together in a polypeptide chain?
What is the primary covalent bond that links amino acids together in a polypeptide chain?
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Which of the following statements about the side chains of alpha amino acids is correct?
Which of the following statements about the side chains of alpha amino acids is correct?
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Which amino acid has an aromatic side chain?
Which amino acid has an aromatic side chain?
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Which of the following amino acids has a sulfur-containing side chain?
Which of the following amino acids has a sulfur-containing side chain?
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What is the primary determinant of an amino acid's unique biochemical properties?
What is the primary determinant of an amino acid's unique biochemical properties?
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Which of the following statements about peptide linkages is correct?
Which of the following statements about peptide linkages is correct?
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Which of the following is true about alpha amino acids?
Which of the following is true about alpha amino acids?
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At physiological pH (pH=7.4), what is the state of the carboxyl and amino groups in amino acids?
At physiological pH (pH=7.4), what is the state of the carboxyl and amino groups in amino acids?
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Which of the following amino acids would be classified as nonpolar?
Which of the following amino acids would be classified as nonpolar?
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What is the general formula for amino acids?
What is the general formula for amino acids?
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Which of the following is not a key function of amino acids in the body?
Which of the following is not a key function of amino acids in the body?
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Which type of side chain is typically found in nonpolar amino acids?
Which type of side chain is typically found in nonpolar amino acids?
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Which of the following is not a common classification of amino acids?
Which of the following is not a common classification of amino acids?
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What type of chemical bond links the amino acids together in a polypeptide chain?
What type of chemical bond links the amino acids together in a polypeptide chain?
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Which of the following is not a characteristic of alpha-amino acids?
Which of the following is not a characteristic of alpha-amino acids?
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What is the primary function of the side chains in amino acids?
What is the primary function of the side chains in amino acids?
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Which of the following statements about non-polar amino acid side chains is correct?
Which of the following statements about non-polar amino acid side chains is correct?
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What is the primary factor that determines the role an amino acid plays in a protein?
What is the primary factor that determines the role an amino acid plays in a protein?
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Which of the following categories are amino acids typically classified into based on their side chain properties?
Which of the following categories are amino acids typically classified into based on their side chain properties?
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What is the primary function of hydrophobic interactions in protein structure?
What is the primary function of hydrophobic interactions in protein structure?
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Which of the following statements about hydrophobes is correct?
Which of the following statements about hydrophobes is correct?
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Which of the following is a characteristic of amino acids with polar side chains?
Which of the following is a characteristic of amino acids with polar side chains?
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Which of the following statements about amino acid side chains (R groups) is correct?
Which of the following statements about amino acid side chains (R groups) is correct?
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Which of the following best describes nonpolar, hydrophobic side chains?
Which of the following best describes nonpolar, hydrophobic side chains?
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What is the primary factor that determines whether an amino acid is classified as essential or nonessential?
What is the primary factor that determines whether an amino acid is classified as essential or nonessential?
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Which of the following statements accurately describes the peptide linkage between amino acids in a polypeptide chain?
Which of the following statements accurately describes the peptide linkage between amino acids in a polypeptide chain?
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Which of the following statements about alpha-amino acids is true?
Which of the following statements about alpha-amino acids is true?
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What is the primary structural difference between a peptide and a polypeptide?
What is the primary structural difference between a peptide and a polypeptide?
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Which of the following statements about conditional amino acids is correct?
Which of the following statements about conditional amino acids is correct?
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What is the primary role of peptide bonds in the structure of proteins?
What is the primary role of peptide bonds in the structure of proteins?
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Which of the following statements about stereoisomers or optical isomers is true?
Which of the following statements about stereoisomers or optical isomers is true?
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Study Notes
Amino Acids
- Amino acids are organic compounds that contain amine (-NH2) and carboxyl (-COOH) functional groups, along with a side chain (R group) specific to each amino acid.
- At physiologic pH (pH=7.4), the carboxyl group is dissociated, forming a negatively charged carboxylate ion, and the amino group is protonated.
- The carbon atom next to the carboxyl group (which is therefore numbered 2 in the carbon chain starting from that functional group) is called the α–carbon.
Classification of Amino Acids
- Amino acids are classified into four categories based on the properties of their side chains: non-polar, polar, acidic, and basic.
- Non-polar amino acids have an even distribution of electrons and do not gain or lose protons or participate in hydrogen or ionic bonds.
- Polar amino acids have an uneven distribution of electrons, such as acids and bases.
- Acidic amino acids have acidic side chains.
- Basic amino acids have basic side chains.
Essential and Non-Essential Amino Acids
- Essential amino acids cannot be made by the body and must come from food.
- There are 9 essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
- Non-essential amino acids are produced by the body and include: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.
- Conditional amino acids are usually not essential, except in times of illness and stress, and include: arginine, cysteine, glutamine, tyrosine, glycine, ornithine, proline, and serine.
Protein Structure
- A polypeptide chain is a series of amino acids joined together in a specific sequence.
- Each amino acid unit in a polypeptide is called a residue.
- Proteins are long chains of amino acids held together by peptide bonds.
- A peptide is two or more amino acids joined together by peptide bonds.
Hydrophobic Interactions
- Hydrophobic interactions describe the relations between water and hydrophobes (low water-soluble molecules).
- Hydrophobes are nonpolar molecules and usually have a long chain of carbons that do not interact with water molecules.
- Non-polar side chains fill up the interior of the folded protein and help give it its three-dimensional shape.
Optical Properties of Amino Acids
- Amino acids that have an asymmetric center at the α–carbon can exist in two forms, designated D and L.
- The two forms in each pair are termed stereoisomers, optical isomers, or enantiomers.
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Description
Test your knowledge on essential and nonessential amino acids with this quiz. Learn about the 9 essential amino acids that must be obtained from food and the nonessential amino acids that our bodies can produce. Identify the differences between essential and nonessential amino acids.