Amino Acids Lecture Flashcards

A set of vocabulary flashcards covering amino acid structures, categories, properties, peptide bonds, protein structural levels, and associated clinical metabolic disorders from the lecture.

Prototypical Amino Acid

A molecule consisting of a central $\alpha$-carbon bonded to four groups: an acidic $\alpha$-carboxylic acid group ($\text{COO}^-$), a basic $\alpha$-amino group ($\text{NH}_3^+$), a hydrogen atom, and a variable functional R group.

L-amino acid form

The stereoisomeric form of an amino acid where the amino group is on the left when aligned with the carboxylic acid at the top; it comprises more than 99% of human amino acids and proteins.

Achiral Amino Acid

An amino acid that lacks non-superimposable mirror images because its R group is a single hydrogen atom, specifically Glycine.

Nonpolar Aliphatic R Groups

A category of amino acids with hydrocarbon side chains that are nonpolar and hydrophobic, including Glycine, Alanine, Valine, Leucine, Isoleucine, Proline, and Methionine.

Proline

An imino acid with its R group cyclized back onto its $\alpha$-amino group, which breaks up $\alpha$-helical secondary structures and is found in structural turns.

Aromatic R Groups

A category of relatively nonpolar and hydrophobic amino acids containing ring structures with cyclic electron delocalization, including Phenylalanine, Tyrosine, and Tryptophan.

Tyrosine

An aromatic amino acid containing a hydroxyl group capable of hydrogen bonding and phosphorylation, making it the most hydrophilic of the aromatic group.

Cystine

A compound formed when two Cysteine residues undergo oxidation to form a covalent disulfide bond, which can be reversed back to Cysteine under reducing conditions.

Insulin Maturation

The processing of Pre-proinsulin into Proinsulin via three disulfide bonds, followed by proteolytic cleavage of peptide C to yield mature insulin composed of two chains held by intermolecular and intramolecular disulfide bonds.

Negatively Charged Polar R Groups

Amino acids containing carboxyl-containing R groups that carry a net $-1$ charge at physiological pH, consisting of Aspartic acid (Aspartate) and Glutamic acid (Glutamate).

Positively Charged Polar R Groups

Hydrophilic amino acids with a net $+1$ charge at physiological pH, comprising Lysine (amino group), Arginine (guanidino group), and Histidine (imidazole group).

pKa

The dissociation constant that indicates whether a functional group will donate or accept a proton ($\text{H}^+$) at a given pH; a group accepts $\text{H}^+$ if pH is less than pKa and donates $\text{H}^+$ if pH is greater than pKa.

Hydropathy Index

A numerical scale reflecting the hydrophobic or hydrophilic nature of an amino acid, where positive numbers indicate hydrophobicity and negative numbers indicate hydrophilicity.

Kinase

An enzyme that adds a phosphate group to the hydroxyl group of Serine, Threonine, or Tyrosine residues, regulating protein activity.

Phosphatase

An enzyme that removes a phosphate group from a phosphorylated amino acid residue to regulate protein activity.

Peptide Bond

A planar covalent bond formed between the $\alpha$-carboxyl group of one amino acid and the $\alpha$-amino group of another via a condensation reaction that releases a molecule of $\text{H}_2\text{O}$.

Primary Structure

The linear sequence of amino acids in a polypeptide chain, written from the $\alpha$-amino-terminal end to the $\alpha$-carboxyl-terminal end.

Secondary Structure

The immediate regional folding of a primary amino acid sequence into stable regional structures like $\alpha$-helices and $\beta$-sheets, mediated by weak interacting forces.

Tertiary Structure

The complete three-dimensional folding arrangement of all secondary structures within a single polypeptide chain, as seen in myoglobin.

Quaternary Structure

The structural conformation and arrangement of two or more polypeptide chains (subunits) within a multi-subunit protein, as seen in hemoglobin.

Cystinuria

An autosomal recessive defect in kidney reabsorption (and intestinal absorption) of Cystine and dibasic amino acids, resulting in Urolithiasis and flat hexagonal Cystine crystals in urine.

Phenylketonuria (PKU)

An autosomal recessive inborn error of metabolism caused by a deficiency in Phenylalanine hydroxylase (PAH) or tetrahydrobiopterin, leading to hyperphenylalaninemia, hyperphenylalaninuria, and a musty diaper odor.

Kuvan (Sapropterin dihydrochloride)

An FDA-approved synthetic form of tetrahydrobiopterin that increases PAH activity to reduce blood Phenylalanine levels in nonclassical PKU patients.

Glutamine

The most abundant amino acid in the human body, acting as a major carrier of ammonia and a nitrogen donor for purine and pyrimidine synthesis.

Glutamate

An acidic amino acid present in the highest concentration in the brain, where it functions as a neurotransmitter.