Protein Structure, Classification & Properties

Vocabulary flashcards covering major terms related to protein structure, classification, properties, and examples.

Primary Structure

The linear sequence of amino acids in a polypeptide chain joined by peptide bonds.

Secondary Structure

Regular folding patterns (α-helix or β-pleated sheet) of a polypeptide stabilized by hydrogen bonds.

α-Helix

A right-handed coil of a polypeptide chain held together by intrachain hydrogen bonds; common in α-keratin.

β-Pleated Sheet

Two or more stretches of polypeptide lying side-by-side, linked by hydrogen bonds; gives silk its strength.

Tertiary Structure

Overall 3-D folding of a single polypeptide, maintained by hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions.

Quaternary Structure

Association of two or more polypeptide chains into a functional protein; stabilized by non-covalent bonds and sometimes disulfide bridges.

Peptide Bond

Covalent bond between the carboxyl group of one amino acid and the amino group of the next.

Hydrogen Bond (in proteins)

Weak attraction between polar side chains or backbone atoms that stabilizes secondary and tertiary structures.

Ionic Bond (Salt Bridge)

Electrostatic attraction between oppositely charged side chains in a protein.

Disulfide Bridge

Covalent S–S bond formed between two cysteine residues, locking parts of a protein together.

Hydrophobic Interaction

Clustering of non-polar side chains away from water, contributing to protein folding.

Fibrous Protein

Long, parallel polypeptide chains forming insoluble, structural proteins (e.g., collagen, keratin).

Globular Protein

Compact, spherical, water-soluble proteins with tertiary (and often quaternary) structure (e.g., enzymes, hemoglobin).

Simple Protein

Protein composed solely of amino acids without additional chemical groups.

Conjugated Protein

Protein combined with a non-protein prosthetic group (e.g., hemoglobin with haem).

Albumin

Water-soluble simple protein found in egg white and blood plasma.

Globulin

Simple protein group that includes antibodies; generally water-insoluble but soluble in dilute salt solutions.

Histone

Positively charged simple protein associated tightly with DNA in chromosomes.

Scleroprotein

Insoluble fibrous protein providing structural support, such as keratin and collagen.

Prosthetic Group

Non-protein component permanently attached to a conjugated protein (e.g., haem, carbohydrate, nucleic acid).

Haem Group

Iron-containing porphyrin ring serving as the oxygen-binding prosthetic group in hemoglobin and myoglobin.

Amphoteric Property

Ability of a protein (or amino acid) to act as both an acid and a base.

Zwitterion

Molecule carrying both positive and negative charges but overall electrically neutral; characteristic of amino acids at their isoelectric point.

Buffering Capacity

Protein’s ability to resist pH changes by accepting or donating H⁺ ions.

Colloidal Property

Proteins form stable dispersions in water rather than true solutions, creating colloids.

Denaturation

Loss of a protein’s native structure due to heat, pH extremes, or chemicals, disrupting bonds that maintain folding.

Renaturation

Refolding of a denatured protein back to its functional conformation under favorable conditions.

Collagen

Triple-helical fibrous protein of connective tissue, providing high tensile strength to skin, tendons and ligaments.

Hemoglobin

Quaternary globular protein in red blood cells with two α and two β chains, each carrying a haem to transport O₂ (and CO₂).

Myoglobin

O₂-binding conjugated protein of muscle, consisting of one polypeptide and one haem group.

Glycoprotein

Conjugated protein with a carbohydrate prosthetic group, e.g., mucin in saliva.

Nucleoprotein

Conjugated protein containing nucleic acid, found in chromosomes and ribosomes.

Casein

Phosphoprotein (conjugated protein with phosphoric acid) that stores amino acids in milk.

Cytochrome Oxidase

Copper-containing conjugated protein functioning as an electron carrier in cellular respiration.

Hydrophobic (Non-polar) Amino Acid

Amino acid whose side chain is non-reactive and repels water, tending to be buried inside proteins.

Hydrophilic (Polar) Amino Acid

Amino acid with a side chain capable of hydrogen bonding; usually exposed on protein surfaces in aqueous environments.