Podcast Beta
Questions and Answers
Which of the following is a characteristic of polar amino acids?
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?
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?
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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?
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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?
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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?
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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?
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Which of the following statements about peptide linkages is correct?
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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?
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Which of the following amino acids would be classified as nonpolar?
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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?
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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?
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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?
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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?
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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?
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What is the primary function of hydrophobic interactions in protein structure?
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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?
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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?
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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?
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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?
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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?
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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.