MCAT: Amino Acids
Master the foundational concepts of amino acids with this comprehensive flashcard deck! Designed for MCAT preparation, it covers essential structures, classifications, properties, and reactions. Boost your understanding of these crucial building blocks of proteins.
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What is the general structure of an α-amino acid?
An α-carbon bonded to an amino group, a carboxyl group, a hydrogen and a variable R group.
Which stereoisomer of amino acids is found in human proteins?
The L form.
Which amino acid is achiral, and why?
Glycine, because its R group is a hydrogen, so the α-carbon has two identical groups.
What bond can two cysteines form?
A disulfide bond, by oxidizing their thiol (–SH) groups; it stabilizes tertiary and quaternary structure.
What is unusual about proline?
Its side chain loops back to the amino nitrogen, forming a ring and a secondary amine that kinks helices.
Name the three aromatic amino acids.
Phenylalanine, tyrosine and tryptophan.
Name the two acidic amino acids.
Aspartate and glutamate, negatively charged at physiological pH.
Name the three basic amino acids.
Lysine, arginine and histidine.
Which basic amino acid is mostly uncharged at pH 7.4?
Histidine, whose side chain pKa is about 6.
Name three nonpolar aliphatic amino acids.
For example alanine, valine and leucine (isoleucine and glycine also qualify).
Name three polar uncharged amino acids.
For example serine, threonine and asparagine (glutamine too).
What kind of reaction forms a peptide bond?
A condensation (dehydration) reaction between one amino acid's carboxyl group and another's amino group, releasing water.
Why is the peptide bond rigid and planar?
Resonance gives the C–N bond partial double-bond character, restricting rotation.
How is the pI of an amino acid without an ionizable side chain calculated?
The average of its α-carboxyl and α-amino pKa values.
Where on a titration curve does an amino acid buffer best?
Near each of its pKa values.
What makes an amino acid essential?
The body cannot make it, so it must come from the diet.