MCAT Biochemistry
Review Questions with
Correct Answers
Amino Acid - Answer:Dipolar compound containing an amino group and a carboxyl group
Amino Group - Answer:-NH2
Carboxyl Group - Answer:-COOH
Alpha Carbon - Answer:Central carbon atom in amino acid
Attached to amino & carboxyl groups, H atom, and side chain
Side Chain - Answer:The variable component of an amino acid that gives the amino acid its identity and
chemical properties
also called R-group
Chiral - Answer:A molecule with a nonsuperimposable mirror image
All amino acids (except glycine) are chiral
(S) Absolute Configuration - Answer:All amino acids (except cysteine) have an (S) absolute configuration
L-amino Acid - Answer:All amino acids found in eukaryotes
Nonpolar, Nonaromatic Amino Acids - Answer:Glycine, alanine, valine, leucine, isoleucine, methionine,
proline
,Glycine - Answer:Single H atom as side chain
Achiral
Smallest amino acid
Alanine - Answer:Alkyl side chain (1C)
Valine - Answer:Alkyl side chain (3C)
Leucine - Answer:Alkyl side chain (4C)
Isoleucine - Answer:Alkyl side chain (4C)
Methionine - Answer:Methyl side chain (-CH3)
Contains S atom in side chain
Proline - Answer:Cyclic amino acid
N from amino group becomes part of side chain, forming five-part ring, limiting where is can appear on a
protein
Rigid/constraints on flexibility
Aromatic Amino Acids - Answer:Tryptophan, phenylalanine, tyrosine
Aromaticity - Answer:The ability of a molecule to delocalize pi electrons around a conjucated ring,
creating exceptional stability
Tryptophan - Answer:Double-ring system
Contains N atom in one ring
Largest of aromatic amino acids
,Phenylalanine - Answer:Benzyl side chain (benzene ring + -CH2 group)
Smallest aromatic amino acid
Relatively nonpolar
Tyrosine - Answer:Phenylalanine + -OH group
Relatively polar
Polar Amino Acids - Answer:Serine, threonine, asparagine, glutamine, cysteine
Polarity - Answer:An uneven sharing of electrons in a molecule, creating a slightly positive side and a
slightly negative side
Serine - Answer:-OH group in side chain
Highly polar - participate in H-bonding
Threonine - Answer:-OH group in side chain
Highly polar - participate in H-bonding
Asparagine - Answer:Amide (-NH2) side chain
Amide N do not gain or lose protons with changes in pH - do not become charged
Glutamine - Answer:Amide (-NH2) side chain
Amide N do not gain or lose protons with changes in pH - do not become charged
Cysteine - Answer:Thiol (-SH) side chain - weaker than OH bond
Prone to oxidation
Negatively-charged (Acidic) Amino Acids - Answer:Aspartic acid (aspartate), glutamic acid (glutamate)
, Aspartic Acid (Aspartate) - Answer:Carboxylate (-COO(-)) group in side chain
Deprotonated form of asparagine
Glutamic Acid (Glutamate) - Answer:Carboxylate (-COO(-)) group in side chain
Deprotonated form of glutamine
Positively-charged (Basic) Amino Acids - Answer:Lysine, arginine, histidine
Lysine - Answer:Terminal primary amino group
Arginine - Answer:Has 3 N atoms in side chain
Charge delocalized over all three N atoms
Histidine - Answer:Has aromatic ring with 2 N atoms (ring is called an imidazole)
At pH 7.4, one N is protonated and the other isn't
Under acidic conditions, the 2nd N becomes protonated, making it positively charged
Hydrophobic Amino Acids - Answer:Being repelled by water
Alanine, isoleucine, leucine, valine, phenylalanine
More likely to be found in center of protein
Nonpolar, uncharged compounds
Long alkyl chains
Hydrophilic Amino Acids - Answer:Being attracted to water
Histidine, arginine, lysine, glutamate, aspartate, asparagine, glutamine
Polar and charged compounds and those that participate in H-bonding
Neither Really Hydrophobic/-philic - Answer:Cysteine, threonine, serine, tyrosine, tryptophan, proline,
methionine, glycine
Review Questions with
Correct Answers
Amino Acid - Answer:Dipolar compound containing an amino group and a carboxyl group
Amino Group - Answer:-NH2
Carboxyl Group - Answer:-COOH
Alpha Carbon - Answer:Central carbon atom in amino acid
Attached to amino & carboxyl groups, H atom, and side chain
Side Chain - Answer:The variable component of an amino acid that gives the amino acid its identity and
chemical properties
also called R-group
Chiral - Answer:A molecule with a nonsuperimposable mirror image
All amino acids (except glycine) are chiral
(S) Absolute Configuration - Answer:All amino acids (except cysteine) have an (S) absolute configuration
L-amino Acid - Answer:All amino acids found in eukaryotes
Nonpolar, Nonaromatic Amino Acids - Answer:Glycine, alanine, valine, leucine, isoleucine, methionine,
proline
,Glycine - Answer:Single H atom as side chain
Achiral
Smallest amino acid
Alanine - Answer:Alkyl side chain (1C)
Valine - Answer:Alkyl side chain (3C)
Leucine - Answer:Alkyl side chain (4C)
Isoleucine - Answer:Alkyl side chain (4C)
Methionine - Answer:Methyl side chain (-CH3)
Contains S atom in side chain
Proline - Answer:Cyclic amino acid
N from amino group becomes part of side chain, forming five-part ring, limiting where is can appear on a
protein
Rigid/constraints on flexibility
Aromatic Amino Acids - Answer:Tryptophan, phenylalanine, tyrosine
Aromaticity - Answer:The ability of a molecule to delocalize pi electrons around a conjucated ring,
creating exceptional stability
Tryptophan - Answer:Double-ring system
Contains N atom in one ring
Largest of aromatic amino acids
,Phenylalanine - Answer:Benzyl side chain (benzene ring + -CH2 group)
Smallest aromatic amino acid
Relatively nonpolar
Tyrosine - Answer:Phenylalanine + -OH group
Relatively polar
Polar Amino Acids - Answer:Serine, threonine, asparagine, glutamine, cysteine
Polarity - Answer:An uneven sharing of electrons in a molecule, creating a slightly positive side and a
slightly negative side
Serine - Answer:-OH group in side chain
Highly polar - participate in H-bonding
Threonine - Answer:-OH group in side chain
Highly polar - participate in H-bonding
Asparagine - Answer:Amide (-NH2) side chain
Amide N do not gain or lose protons with changes in pH - do not become charged
Glutamine - Answer:Amide (-NH2) side chain
Amide N do not gain or lose protons with changes in pH - do not become charged
Cysteine - Answer:Thiol (-SH) side chain - weaker than OH bond
Prone to oxidation
Negatively-charged (Acidic) Amino Acids - Answer:Aspartic acid (aspartate), glutamic acid (glutamate)
, Aspartic Acid (Aspartate) - Answer:Carboxylate (-COO(-)) group in side chain
Deprotonated form of asparagine
Glutamic Acid (Glutamate) - Answer:Carboxylate (-COO(-)) group in side chain
Deprotonated form of glutamine
Positively-charged (Basic) Amino Acids - Answer:Lysine, arginine, histidine
Lysine - Answer:Terminal primary amino group
Arginine - Answer:Has 3 N atoms in side chain
Charge delocalized over all three N atoms
Histidine - Answer:Has aromatic ring with 2 N atoms (ring is called an imidazole)
At pH 7.4, one N is protonated and the other isn't
Under acidic conditions, the 2nd N becomes protonated, making it positively charged
Hydrophobic Amino Acids - Answer:Being repelled by water
Alanine, isoleucine, leucine, valine, phenylalanine
More likely to be found in center of protein
Nonpolar, uncharged compounds
Long alkyl chains
Hydrophilic Amino Acids - Answer:Being attracted to water
Histidine, arginine, lysine, glutamate, aspartate, asparagine, glutamine
Polar and charged compounds and those that participate in H-bonding
Neither Really Hydrophobic/-philic - Answer:Cysteine, threonine, serine, tyrosine, tryptophan, proline,
methionine, glycine
