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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 alpha-amino acid?
An alpha-amino acid consists of a central alpha carbon bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R-group).
Which stereoisomeric form of amino acids is found in proteins in eukaryotes?
Almost all amino acids found in eukaryotic proteins are in the L-configuration, meaning the amino group is on the left in a Fischer projection.
What is unique about glycine's structure and its chirality?
Glycine has a hydrogen atom as its R-group, making it the only achiral amino acid because its alpha carbon is not bonded to four different groups.
What is special about cysteine's side chain and its role in protein structure?
Cysteine's side chain contains a thiol (-SH) group, which can oxidize to form a disulfide bond with another cysteine, crucial for tertiary and quaternary protein structure.
What is unique about proline's side chain structure?
Proline has a cyclic structure where its amino group is incorporated into a five-membered ring with its alpha carbon and R-group, creating a secondary amine rather than a primary one.
Name three nonpolar, aliphatic amino acids.
Valine, Leucine, and Alanine are common examples of nonpolar, aliphatic amino acids. Other examples include Glycine, Isoleucine, and Methionine.
Name the three aromatic amino acids.
The three aromatic amino acids are Phenylalanine, Tyrosine, and Tryptophan, all containing a benzene ring or a derivative.
Name three polar, uncharged amino acids.
Serine, Threonine, and Asparagine are common examples of polar, uncharged amino acids. Other examples include Glutamine and Cysteine.
Name the two acidic amino acids and their general charge at physiological pH (pH 7.4).
The two acidic amino acids are Aspartate (aspartic acid) and Glutamate (glutamic acid); both have a negatively charged carboxyl group in their side chain at physiological pH.
Name the three basic amino acids and their general charge at physiological pH (pH 7.4).
The three basic amino acids are Lysine, Arginine, and Histidine; Lysine and Arginine are positively charged, while Histidine can be neutral or positively charged depending on the exact pH.
How is a peptide bond formed between two amino acids?
A peptide bond is formed by a dehydration reaction (condensation reaction) between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water.
Describe the key characteristics of a peptide bond.
A peptide bond has partial double-bond character due to resonance, making it rigid and planar, and restricting rotation around the C-N bond.
How is the isoelectric point (pI) of an amino acid without an ionizable side chain calculated?
The pI for an amino acid without an ionizable side chain is calculated as the average of its pKa values for the alpha-carboxyl group and the alpha-amino group: pI = (pKa(COOH) + pKa(NH2)) / 2.
Where do amino acids exhibit buffering capacity on a titration curve?
Amino acids exhibit buffering capacity in the regions around their pKa values, specifically around the pKa of the carboxyl group, the amino group, and any ionizable side chains.
What defines an 'essential' amino acid?
An essential amino acid is one that cannot be synthesized by the human body and must therefore be obtained through dietary intake.