Module 09: Nitrogen Functional Groups

Vocabulary practice flashcards covering structures, classifications, nomenclature, physical properties, chemical reactions, and conformational levels of amines, amides, amino acids, and proteins.

Amine

An organic compound derived from ammonia ($NH_3$) in which one or more hydrogen atoms are replaced by alkyl or aromatic hydrocarbon groups.

Amide

An organic compound containing a carbonyl group bonded directly to a nitrogen atom, formed by the reaction of a carboxylic acid derivative (such as an acid chloride or acid anhydride) with an amine.

Primary ($1^\circ$) Amine

An amine in which exactly one carbon group is bonded to the nitrogen atom ($R\text{-}NH_2$), retaining two hydrogen atoms.

Secondary ($2^\circ$) Amine

An amine in which two carbon groups are bonded to the nitrogen atom ($R_1\text{-}NH\text{-}R_2$), leaving one hydrogen atom on the nitrogen.

Tertiary ($3^\circ$) Amine

An amine in which three carbon groups are bonded to the nitrogen atom ($R_1 R_2 R_3 N$); it cannot react with acid derivatives to form amides because the nitrogen lacks a hydrogen atom to lose.

Quaternary ($4^\circ$) Amine

An ionic compound in which the nitrogen atom uses its lone pair of electrons to bond to a fourth carbon group, imparting a positive formal charge to the nitrogen atom alongside an anion.

Aniline

The simplest aromatic amine, consisting of an amino group ($-NH_2$) directly attached to a benzene ring.

Heterocyclic Amines

Cyclic organic compounds containing at least one nitrogen atom as part of the ring system, classified as aliphatic (such as pyrrolidine and piperidine) or aromatic (such as pyridine, pyrimidine, imidazole, and purine).

Trimethylamine

A low-molecular-weight tertiary amine with a sharp, penetrating odor responsible for the characteristic smell of rotten fish.

Amine Salt

An ionic compound formed when the lone pair of electrons on the nitrogen atom of an amine acts as a weak base and accepts a hydrogen ion ($H^+$) from an acid, following the reaction $R\text{-}NH_2 + HX \rightarrow R\text{-}NH_3^+ + X^-$.

Amide Hydrolysis

The cleavage of an amide bond by water in the presence of heat and a strong acid or base catalyst, producing a carboxylic acid and an amine salt in acidic conditions, or a carboxylate salt and an amine in basic conditions.

$\alpha$-Amino Acid

A monomer unit of proteins that contains both an amino group ($-NH_2$) and a carboxylic acid group ($-COOH$) bonded to the same neighboring alpha carbon atom.

Zwitterion

A dipolar, overall neutral ionic form of an amino acid where the carboxylic acid group has donated a proton to the amino group, producing a $-COO^-$ and a $-NH_3^+$ group.

Isoelectric Point ($pI$)

The specific pH at which an amino acid carries no net electrical charge and exists predominantly in its zwitterionic form.

Peptide Bond

The covalent amide linkage connecting the alpha-carboxyl group of one amino acid to the alpha-amino group of an adjacent amino acid, named by Emil Fischer in 1902.

N-Terminal Amino Acid

The amino acid residue at the beginning of a polypeptide chain possessing an unbonded, free $-NH_3^+$ group, written by convention on the far left.

C-Terminal Amino Acid

The amino acid residue at the end of a polypeptide chain possessing an unbonded, free $-COO^-$ group, written by convention on the far right.

Primary ($1^\circ$) Structure

The specific linear sequence of amino acids linked together by covalent peptide bonds along a polypeptide chain.

Secondary ($2^\circ$) Structure

The localized, orderly geometric arrangements of the polypeptide backbone held together by hydrogen bonds between the carbonyl oxygen and amide hydrogen atoms of peptide links.

$\alpha$-Helix

A secondary protein structure characterized by a right-handed coiled spiral stabilized by intrachain hydrogen bonds between amide groups, with all side-chain $R$ groups projecting outward.

$\beta$-Pleated Sheet

A secondary protein structure formed by neighboring polypeptide strands aligned parallel or antiparallel, held together by interstrand hydrogen bonds, with $R$ groups alternating above and below the sheet plane.

Tertiary ($3^\circ$) Structure

The overall three-dimensional folding pattern of an entire single polypeptide chain, stabilized by interactions among amino acid side chains including disulfide bonds, salt bridges, hydrogen bonds, and hydrophobic interactions.

Disulfide Bond

A strong covalent link ($-CH_2\text{-}S\text{-}S\text{-}CH_2\text{-}$) formed by the oxidation of the sulfhydryl ($-SH$) groups of two cysteine residues within a polypeptide chain.

Salt Bridge

An electrostatic attraction in tertiary protein structure occurring between the negatively charged carboxylate ion ($-COO^-$) of an acidic side chain and the positively charged ammonium ion ($-NH_3^+$) of a basic side chain.

Quaternary ($4^\circ$) Structure

The spatial aggregation and non-covalent structural organization of two or more independent polypeptide subunits into a single functional biological macromolecule.

Hemoglobin

A transport protein demonstrating quaternary structure, composed of two alpha chains (141 amino acids each) and two beta chains (146 amino acids each), each surrounding an iron-containing heme prosthetic group that binds oxygen.

Denaturation

The process of disrupting the secondary, tertiary, or quaternary native structural conformations of a protein through physical or chemical agents (such as heat, UV light, heavy metals, detergents, or extreme pH), rendering it biologically inactive without breaking covalent peptide bonds.