Amino Acids and Proteins - Vocabulary Flashcards (Chapter 18)

Vocabulary flashcards covering key terms and definitions from Chapter 18: Amino Acids and Proteins.

Biochemistry

The study of molecules and reactions in living organisms, including inorganic and organic principles, with the goal of understanding structure and function.

Protein

A polymer of amino acids that performs structural, enzymatic, signaling, and other essential biological roles.

Amino Acid

The building block of proteins, containing an amino group, a carboxyl group, a hydrogen, and a variable R-group attached to a central alpha carbon.

Alpha (α) Carbon

The central carbon of an amino acid to which the NH2, COOH, H, and R-group are attached.

Zwitterion

A neutral dipolar ion with one positive and one negative charge; amino acids exist as zwitterions at physiological pH.

Isoelectric Point (pI)

The pH at which an amino acid has equal positive and negative charges, giving a net charge of zero.

Peptide Bond

An amide bond formed between the carboxyl group of one amino acid and the amino group of the next, releasing water.

Dipeptide

A molecule formed when two amino acids are linked by a single peptide bond.

Tripeptide

A short chain of three amino acids linked by peptide bonds.

Polypeptide

A long chain of amino acids; a protein or protein segment.

N-terminus

The amino-terminal end of a peptide or protein (left side) where the first amino acid resides.

C-terminus

The carboxyl-terminal end (right side) where the last amino acid resides.

Primary Structure

The linear sequence of amino acids in a protein, held together by peptide bonds.

Secondary Structure

Local folded structures of a protein, mainly alpha-helices and beta-sheets, stabilized by backbone hydrogen bonds.

Alpha-helix (α-helix)

A right-handed coil stabilized by hydrogen bonds between backbone amide N–H and carbonyl C=O groups.

Beta-sheet (β-sheet)

A sheet-like arrangement formed by hydrogen bonds between backbone atoms of adjacent polypeptide strands.

Tertiary Structure

The overall three-dimensional folding of a single polypeptide, stabilized by various noncovalent interactions and disulfide bonds.

Disulfide Bond

A covalent S–S bond between cysteine side chains that can stabilize a protein's tertiary or quaternary structure.

Quaternary Structure

The assembly of two or more polypeptide chains into a functional protein, held together by noncovalent interactions (and sometimes covalent bonds).

Conjugated Proteins

Proteins that contain non-amino acid prosthetic groups (e.g., heme, carbohydrates, lipids, metals) that contribute to function.

Hydrophobic Interactions

Nonpolar R-groups cluster inside the protein away from water, driven by the hydrophobic effect to stabilize structure.

Hydrophilic R-group

Polar or charged side chains that interact with water and aid solubility and folding.

Essential Amino Acids

Amino acids that must be obtained from the diet because humans cannot synthesize them.

Proline

An α-amino acid with a secondary amine in a five-membered ring, giving it unique conformational properties.

Glycine

The simplest amino acid; achiral because its side chain is a single hydrogen.

Aromatic Amino Acids

Amino acids with aromatic side chains: phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp).

Endoprotease

Enzymes that hydrolyze peptide bonds at internal sites (e.g., chymotrypsin, trypsin, pepsin; carboxypeptidases act at ends).

Denaturation

Loss of secondary, tertiary, and/or quaternary structure (primary structure remains); often reduces solubility and function.

Hemoglobin

A conjugated quaternary protein with four polypeptide chains and four heme groups; transports oxygen in blood.

Heme

Iron-containing prosthetic group bound to heme proteins (e.g., hemoglobin, myoglobin) that binds oxygen.

Myoglobin

Globular protein that stores oxygen in muscle tissue and contains a heme group.

Fibrous vs Globular Proteins

Fibrous proteins are insoluble and form fibers; globular proteins are folded into compact, soluble shapes (often enzymes or transport proteins).

Hydrogen Bond (in Proteins)

A noncovalent interaction between N–H and C=O groups that stabilizes secondary (and tertiary) structures.

CHONPS

Elements commonly found in biomolecules: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, and Sulfur.

Proteolysis / Protein Hydrolysis

Chemical or enzymatic cleavage of peptide bonds to yield amino acids; occurs in digestion and laboratory hydrolysis.