Amino Acids - Biochemistry (Nursing) Module #5

Vocabulary flashcards covering key terms and definitions from the amino acids notes (Pages 1–4).

Amino acid

Building blocks of proteins; fundamental sub-units with an amino group, a carboxyl group, an α-carbon bearing a side chain (R).

Amino group

NH2 functional group; basic, accepts a proton (becomes –NH3+ in many environments).

Carboxyl group

COOH functional group; acidic, donates a proton (forms –COO− when deprotonated).

R group (side chain)

Variable group attached to the α-carbon; determines the amino acid’s properties (polar, nonpolar, acidic, basic, etc.).

Amphoteric

Amino acids can act as both acids (donate a proton) and bases (accept a proton).

Zwitterion

A molecule with both positive and negative charges but zero net charge; common form of amino acids near neutral pH.

Isoelectric point (pI)

pH at which an amino acid exists as a zwitterion with zero net charge; used in buffering and separation; examples include Asp 2.8, Glu 3.2, Ser 5.7, Ala 6.1, Lys 9.7, Arg 10.8.

Optical activity

Ability of a molecule to rotate plane-polarized light; due to a chiral α-carbon in most amino acids (glycine is not chiral).

Dextrorotatory

Rotation of plane-polarized light to the right (positive direction).

Levorotatory

Rotation of plane-polarized light to the left (negative direction).

Chiral center

Asymmetric α-carbon bonded to four different substituents; responsible for optical activity in most amino acids.

Glycine

Simplest amino acid; side chain is hydrogen; not optically active.

Essential amino acids

Amino acids that cannot be synthesized by the body and must be obtained from the diet.

Non-essential (dispensable) amino acids

Amino acids that can be synthesized by the body.

Conditionally essential amino acids

Normally nonessential but become essential during illness or physiological stress.

Branched-chain amino acids (BCAA)

Valine, Leucine, and Isoleucine; have branched aliphatic side chains and are essential.

Aromatic amino acids

Phenylalanine, Tyrosine, Tryptophan; contain aromatic rings; phenylalanine is nonpolar, tyrosine is polar due to the hydroxyl group.

Sulfur-containing amino acids

Methionine and Cysteine; contain sulfur; methionine is essential; cysteine forms disulfide bonds.

Hydroxy-containing amino acids

Serine, Threonine, and Tyrosine (and others with –OH groups) that contain hydroxyl groups.

Imino acids

Proline and Hydroxyproline; contain an imino group (NH) rather than a typical amino NH2; often form rings.

Dipeptide

Two amino acids joined by a peptide bond; formed by dehydration; diketopiperazine is a cyclic form from dehydration; acid hydrolysis yields a dipeptide.

Polypeptide

Long chains of amino acids linked by peptide bonds; basic building blocks of proteins.

Diketopiperazine

Cyclized product formed when two amino acids dehydrate; under certain conditions can yield a dipeptide upon hydrolysis.

Fischer peptide synthesis

A method used to synthesize polypeptides from amino acids under controlled conditions.

Nitrous acid reaction (Van Slyke reaction)

Nitrous acid reacts with amino groups to release nitrogen gas; used to detect or quantify amino groups in proteins and amino acids.

Formaldehyde reaction (Sorensen test)

Excess neutral formaldehyde with amino acids produces an acidic mixture; methylene replacement of amine hydrogens; titration measures free carboxyl groups—basis of the Sorensen test.

Amino acid

Building blocks of proteins; fundamental sub-units with an amino group, a carboxyl group, an α-carbon bearing a side chain (R).

Amino group

NH2 functional group; basic, accepts a proton (becomes –NH3+ in many environments).

Carboxyl group

COOH functional group; acidic, donates a proton (forms –COO− when deprotonated).

R group (side chain)

Variable group attached to the α-carbon; determines the amino acid’s properties (polar, nonpolar, acidic, basic, etc.).

Amphoteric

Amino acids can act as both acids (donate a proton) and bases (accept a proton).

Zwitterion

A molecule with both positive and negative charges but zero net charge; common form of amino acids near neutral pH.

Isoelectric point (pI)

pH at which an amino acid exists as a zwitterion with zero net charge; used in buffering and separation; examples include Asp 2.8, Glu 3.2, Ser 5.7, Ala 6.1, Lys 9.7, Arg 10.8.

Optical activity

Ability of a molecule to rotate plane-polarized light; due to a chiral α-carbon in most amino acids (glycine is not chiral).

Dextrorotatory

Rotation of plane-polarized light to the right (positive direction).

Levorotatory

Rotation of plane-polarized light to the left (negative direction).

Chiral center

Asymmetric α-carbon bonded to four different substituents; responsible for optical activity in most amino acids.

Glycine

Simplest amino acid; side chain is hydrogen; not optically active.

Essential amino acids

Amino acids that cannot be synthesized by the body and must be obtained from the diet.

Non-essential (dispensable) amino acids

Amino acids that can be synthesized by the body.

Conditionally essential amino acids

Normally nonessential but become essential during illness or physiological stress.

Branched-chain amino acids (BCAA)

Valine, Leucine, and Isoleucine; have branched aliphatic side chains and are essential.

Aromatic amino acids

Phenylalanine, Tyrosine, Tryptophan; contain aromatic rings; phenylalanine is nonpolar, tyrosine is polar due to the hydroxyl group.

Sulfur-containing amino acids

Methionine and Cysteine; contain sulfur; methionine is essential; cysteine forms disulfide bonds.

Hydroxy-containing amino acids

Serine, Threonine, and Tyrosine (and others with –OH groups) that contain hydroxyl groups.

Imino acids

Proline and Hydroxyproline; contain an imino group (NH) rather than a typical amino NH2; often form rings.

Dipeptide

Two amino acids joined by a peptide bond; formed by dehydration; diketopiperazine is a cyclic form from dehydration; acid hydrolysis yields a dipeptide.

Polypeptide

Long chains of amino acids linked by peptide bonds; basic building blocks of proteins.

Diketopiperazine

Cyclized product formed when two amino acids dehydrate; under certain conditions can yield a dipeptide upon hydrolysis.

Fischer peptide synthesis

A method used to synthesize polypeptides from amino acids under controlled conditions.

Nitrous acid reaction (Van Slyke reaction)

Nitrous acid reacts with amino groups to release nitrogen gas; used to detect or quantify amino groups in proteins and amino acids.

Formaldehyde reaction (Sorensen test)

Excess neutral formaldehyde with amino acids produces an acidic mixture; methylene replacement of amine hydrogens; titration measures free carboxyl groups—basis of the Sorensen test.

Peptide bond

An amide bond formed between the carboxyl group of one amino acid and the amino group of another, linking amino acids into polypeptides. It is rigid and planar.

Primary protein structure

The unique, linear sequence of amino acids in a polypeptide chain, determined by genetic information.

Secondary protein structure

Local folding patterns within a polypeptide stabilized by hydrogen bonds, primarily forming α-helices and β-pleated sheets.

Alpha-helix (\alpha-helix)

A common secondary protein structure; a right-handed coiled structure stabilized by hydrogen bonds between amino and carboxyl groups of amino acids spaced four residues apart.

Beta-pleated sheet (\beta-sheet)

A common secondary protein structure; formed by hydrogen bonds between backbone atoms of adjacent polypeptide strands, which lie side