Amines, Amides, Amino Acids, Proteins, and Enzymes

Comprehensive vocabulary flashcards covering the IUPAC nomenclature, structure, chemical reactions, physiological roles, and classification of amines, amides, amino acids, proteins, and enzymes.

Amine

A derivative of ammonia ($\text{NH}_3$) in which one or more hydrogen atoms are replaced with alkyl or aromatic groups.

Primary ($1^\circ$) Amine

An amine in which exactly one carbon group is bonded directly to the nitrogen atom.

Secondary ($2^\circ$) Amine

An amine in which two carbon groups are bonded directly to the nitrogen atom.

Tertiary ($3^\circ$) Amine

An amine in which three carbon groups are bonded directly to the nitrogen atom.

Aniline

The IUPAC name for the aromatic amine of benzene ($\text{C}_6\text{H}_5\text{NH}_2$), which is used in manufacturing dyes for wool, cotton, silk, and denim.

Ammonium Salt

An ionic compound formed when an amine acts as a Brønsted–Lowry base and accepts a proton ($\text{H}^+$) from an acid, producing a positively charged alkylammonium cation and an anion.

Quaternary ($4^\circ$) Ammonium Salt

A nitrogen-containing compound in which the nitrogen atom is bonded to four carbon groups, carrying a permanent positive charge without being bonded to any hydrogen atoms.

Heterocyclic Amine

A cyclic organic compound that consists of a ring of five or six atoms, of which one or two are nitrogen atoms.

Alkaloids

Physiologically active, habit-forming nitrogen compounds produced by plants that contain heterocyclic amines, such as nicotine, caffeine, morphine, and codeine.

Neurotransmitter

A chemical compound that transmits an electrical impulse from a nerve cell across a synapse to a target cell (such as another neuron, muscle, or gland).

Synapse

The junction formed between the axon terminal of a transmitting neuron and the dendrites of a neighboring receiving cell.

Acetylcholine

A neurotransmitter synthesized from acetate and choline that communicates between the nervous system and muscle cells to regulate muscle contraction, learning, and short-term memory.

Catecholamines

A family of structurally related neurotransmitters synthesized from the amino acid tyrosine, including dopamine, norepinephrine, and epinephrine.

Dopamine

A catecholamine natural stimulant produced in the midbrain that regulates muscle movement, cognition, sleep–wake cycles, and feelings of enjoyment.

Serotonin

An inhibitory neurotransmitter synthesized from tryptophan that helps promote relaxation, peaceful sleep, calmness, and emotional well-being.

GABA ($\gamma$-Aminobutyric Acid)

The most common inhibitory neurotransmitter in the brain, produced from glutamate, which reduces anxiety and helps regulate muscle tone and sleep.

Amide

A derivative of a carboxylic acid in which a nitrogen group replaces the hydroxyl ($-\text{OH}$) group.

Amidation

A condensation reaction in which a carboxylic acid reacts with ammonia or a primary or secondary amine under heat to form an amide and water.

Urea

The simplest natural amide, formed as the final end product of protein metabolism and excreted in urine.

Acid Hydrolysis of Amides

A reaction in which an amide reacts with water and an acid under heat to produce a carboxylic acid and an ammonium salt.

Base Hydrolysis of Amides

A reaction in which an amide reacts with a strong base under heat to yield a carboxylate salt and an amine or ammonia.

Amino Acid

A molecular building block of proteins containing a central $\alpha$-carbon bonded to an ammonium group ($-\text{NH}_3^+$), a carboxylate group ($-\text{COO}^-$), a hydrogen atom, and a distinctive R group.

Essential Amino Acids

The nine amino acids that cannot be synthesized by the human body and must be supplied through dietary protein intake.

Peptide Bond

An amide bond linking two amino acids, formed between the carboxylate group ($-\text{COO}^-$) of one amino acid and the ammonium group ($-\text{NH}_3^+$) of the next.

Primary Structure of Proteins

The unique, linear sequence of amino acids joined together by covalent peptide bonds in a polypeptide chain.

Secondary Structure of Proteins

The localized folding of a polypeptide chain held together by hydrogen bonds between the backbone $C=\text{O}$ and $N-\text{H}$ groups, typically forming an $\alpha$-helix or a $\beta$-pleated sheet.

Alpha ($\alpha$) Helix

A helical secondary protein structure resembling a coiled staircase, stabilized by hydrogen bonds between carbonyl oxygen atoms and amide nitrogen protons along the backbone.

Beta ($\beta$)-Pleated Sheet

A secondary protein structure wherein polypeptide chains lie side-by-side in a sheet-like arrangement stabilized by hydrogen bonds between adjacent backbone segments.

Triple Helix

A fibrous secondary protein structure consisting of three polypeptide chains woven together like a rope, characteristic of collagen.

Tertiary Structure of Proteins

The overall three-dimensional folding of a single polypeptide chain determined by interactions and repulsions among the amino acid R groups.

Salt Bridge

An ionic attraction in a protein's tertiary structure occurring between the ionized R groups of an acidic amino acid and a basic amino acid.

Disulfide Bond

A covalent bond ($-\text{S}-\text{S}-$) formed by the oxidation of thiol ($-\text{SH}$) groups between two cysteine residues within a protein.

Quaternary Structure of Proteins

The structural level of a biologically active protein composed of two or more individual polypeptide chains (subunits) maintained by noncovalent interactions and disulfide links.

Protein Denaturation

The disruption of hydrogen bonds, hydrophobic interactions, salt bridges, or disulfide linkages that stabilize secondary, tertiary, or quaternary protein structure, rendering the protein biologically inactive.

Enzyme

A biological catalyst, usually a globular protein, that increases the velocity of a biochemical reaction by lowering its activation energy.

Active Site

A pocket or groove on the tertiary structure of an enzyme containing catalytic R groups where substrate molecules bind.

Induced-Fit Model

A dynamic model of enzyme catalysis wherein the flexible active site and substrate adjust their shapes to achieve an optimal fit that lowers activation energy.

Oxidoreductases

An enzyme classification encompassing enzymes that catalyze oxidation-reduction reactions, including oxidases and dehydrogenases.

Transferases

An enzyme classification that catalyzes the transfer of functional groups (such as amino or phosphate groups) from one molecule to another.

Hydrolases

An enzyme classification that catalyzes cleavage reactions involving the addition of water, such as peptidases, lipases, and nucleases.

Lyases

An enzyme classification that catalyzes the addition or elimination of chemical groups to form double bonds without hydrolysis.

Isomerases

An enzyme classification that catalyzes the rearrangement of atoms within a single substrate to produce an isomer.

Ligases

An enzyme classification that catalyzes the joining of two molecules coupled with the hydrolysis of ATP.

Allosteric Enzyme

An enzyme that contains a regulatory binding site distinct from the active site; binding of an effector molecule changes the active site's shape to increase or decrease catalytic activity.

Feedback Control

A regulatory mechanism in which the accumulated end product of a multi-step pathway acts as an allosteric inhibitor on the first enzyme, turning off the pathway.

Zymogen

An inactive precursor form of an enzyme (proenzyme) that requires covalent cleavage of one or more peptide bonds to become catalytically active.

Isoenzymes

Multiple forms of the same enzyme that catalyze the same biochemical reaction but have slightly different amino acid compositions and exist in different tissues.

Competitive Inhibitor

An inhibitor molecule whose chemical structure resembles that of the substrate and competes directly for binding at the active site; its effect is reversed by increasing substrate concentration.

Noncompetitive Inhibitor

An inhibitor that binds to an enzyme away from the active site, altering the enzyme's three-dimensional shape and preventing catalysis regardless of substrate concentration.

Irreversible Inhibitor

A compound that destroys enzyme activity permanently by forming a covalent bond with an amino acid R group at or near the active site.

Cofactor

A non-protein metal ion or organic molecule required by an enzyme to form a catalytically active complex.

Coenzyme

An organic cofactor, frequently derived from water-soluble vitamins, that participates directly in the catalytic action of an enzyme by transferring electrons or chemical groups.