Amino Acids, Peptides, and Proteins

Vocabulary practice flashcards covering core concepts of amino acid chemistry, peptide structure, ionization properties, non-standard amino acids, and protein purification techniques based on Lehninger Principles of Biochemistry.

Keratin

A fibrous structural protein found in all vertebrates that serves as the chief structural component of hair, scales, horns, wool, nails, and feathers.

Chirality

The structural property of an object or molecule that is non-superimposable on its mirror image, as seen in all standard amino acids except glycine.

Zwitterion

A dipolar molecule containing spatially separated positive and negative charged functional groups, resulting in a net electrical charge of zero.

Isoelectric Point ($pI$)

The specific pH at which a molecule or protein carries a net charge of zero and does not migrate in an electric field.

Enantiomers

Nonsuperimposable mirror-image stereoisomers that possess identical physical properties except for the direction in which they rotate plane-polarized light.

Ibuprofen Enantiomers

Chiral forms of an anti-inflammatory drug where the $S(+)$-enantiomer actively inhibits cyclooxygenase (COX), whereas the $R(-)$-enantiomer is inactive against COX and is incorporated into triglycerides.

Cystine

The dimeric amino acid formed when two cysteine residues undergo oxidation to create a covalent disulfide bond.

Selenocysteine

An uncommon amino acid containing a selenium atom in place of sulfur, inserted into proteins during translation via a specialized $UGA$ stop codon.

Peptide Bond

A substituted amide linkage formed through a condensation reaction between the \text{\tau-carboxyl} group of one amino acid and the \text{\tau-amino} group of another.

Cation-Exchange Chromatography

A column purification technique using a solid matrix with negatively charged functional groups to retain positively charged proteins while allowing negatively charged proteins to elute earlier.

Size-Exclusion Chromatography

A separation technique using porous polymer beads through which larger protein molecules elute earlier while smaller molecules enter bead pores and are retarded.

Affinity Chromatography

A column separation method that isolates a target protein based on its specific, non-covalent binding interaction with a polymer-bound ligand.

Sodium Dodecyl Sulfate (SDS)

An anionic detergent used in gel electrophoresis to denature proteins and impart a uniform negative charge-to-mass ratio, allowing separation solely by molecular weight.

Isoelectric Focusing

An electrophoretic method that separates proteins within a stationary pH gradient until each protein reaches the region equal to its isoelectric point ($pI$).

Two-Dimensional (2D) Gel Electrophoresis

A high-resolution analytical technique combining isoelectric focusing in the first dimension (separating by $pI$) with SDS-PAGE in the second dimension (separating by molecular weight $M_r$).

Beer-Lambert Law

The mathematical relationship A = \text{\tau} c l expressing UV-visible light absorbance $A$ as a linear function of molar absorptivity \text{\tau}, solute concentration $c$, and path length $l$.

Specific Activity

The ratio of total enzyme or protein activity units to total protein concentration or mass, serving as a quantitative measure of purity during protein isolation.

Edman Degradation

A classical chemical sequencing method that labels and cleaves the N-terminal amino acid residue of a peptide using phenylisothiocyanate under basic and acidic conditions.

Matrix-Assisted Laser Desorption/Ionization (MALDI)

A soft ionization mass spectrometry method where short laser pulses desorb and ionize macromolecules co-crystallized with an light-absorbing chemical matrix.

Electrospray Ionization (ESI)

A mass spectrometry ionization technique where a high-voltage capillary disperses a liquid protein sample into microdroplets, generating intact gas-phase ions.

GABA (\text{\tau}-Aminobutyric Acid)

A major inhibitory neurotransmitter in the brain formed via the enzymatic decarboxylation of glutamate.

Histamine

A amine signaling molecule involved in inflammatory and allergic responses, produced by the decarboxylation of histidine.

Ornithine

A non-proteinogenic amino acid that serves as a critical metabolic intermediate in the urea cycle and arginine biosynthesis.