Proteins and Protein Structure

Vocabulary practice flashcards covering protein structures, levels of organization, chemical bonds, disease mutations, and post-translational modifications based on the lecture notes.

Alpha-keratin

A structural protein that forms hair and fingernails, and serves as the major component of feathers, wool, claws, scales, horns, and hooves.

Actin and Myosin

Muscle proteins that enable all muscular movement in the body, ranging from blinking and breathing to rollerblading.

Hemoglobin

A transport protein composed of four polypeptide subunits and iron-containing ($Fe^{2+}$) heme groups that carries oxygen in the blood to every part of the body.

Ion Channel Proteins

Membrane proteins that control brain signaling by regulating the flow of small molecules and ions into and out of nerve cells.

Collagen

A structural protein present in cartilage and tendons that derives its high tensile strength from a three-stranded, rope-like conformation.

DNA Polymerase III

A donut-shaped enzyme that regulates genetic material activity by forming a complete circular ring around the DNA molecule.

Titin

The largest human protein known, composed of $34{,}350$ amino acids.

Glutathione

The smallest functional polypeptide in humans, consisting of only three amino acids.

Enkephalins

Pentapeptides (five-amino-acid polypeptides) that bind to opioid receptors in the body to regulate nociception.

R Group

The variable side chain bonded to the central $\alpha$-carbon of an amino acid that is unique to each amino acid and dictates its chemical properties and functional role.

Proline

An imino acid whose aliphatic side chain is covalently bonded to both the backbone nitrogen and carbon atoms, creating a rigid cyclic structure with a secondary amino group commonly located at bends in proteins.

Primary Structure

The linear sequence of amino acids linked together by covalent peptide bonds within a polypeptide, reported from the N-terminus to the C-terminus.

Peptide Bond

A strong, covalent amide linkage formed between the carboxyl group of one amino acid and the amino group of another via a condensation reaction that releases water ($H_2O$).

Secondary Structure

Local spatial arrangements of the polypeptide backbone, most commonly forming $\alpha$-helices and $\beta$-pleated sheets, stabilized by hydrogen bonding between donor and acceptor groups along the peptide backbone.

Tertiary Structure

The overall three-dimensional folding of an entire polypeptide chain into its lowest energy state, stabilized by hydrogen bonds, van der Waals forces, hydrophobic interactions, ionic bonds, and disulphide bridges between R groups.

Quaternary Structure

The multi-subunit assembly and spatial arrangement produced when two or more distinct polypeptide chains interact to form a functional aggregate protein complex.

Salt Bridge

A stabilizing non-covalent structural interaction combining an ionic bond (electrostatic attraction between oppositely charged side chains) with a hydrogen bond.

Disulphide Bond

A covalent sulphur–sulphur linkage ($-CH_2-S-S-CH_2-$) formed between the sulfhydryl side chains of two cysteine residues.

Hydrophobic Interactions

The non-covalent thermodynamic driving force that causes nonpolar amino acid side chains to pack tightly inside the interior core of a protein to minimize contact with water.

van der Waals Forces

Weak, transient intermolecular attractions between atoms and molecules generated by temporary dipole-dipole interactions.

Sickle Cell Disease

An inherited red blood cell condition caused by a single nucleotide substitution changing a glutamic acid codon ($GAG$) to a valine codon ($GTG$) in the $\beta$-globin chain, resulting in sickled cells and blocked blood flow.

CFTR Protein

A membrane-bound chloride ion channel; mutations such as G551D (door-jamming functional defect) or $\Delta F508$ (trafficking/location defect) prevent normal chloride conductance, leading to cystic fibrosis.

Lactose Intolerance

The impaired ability to digest lactose, caused in infants by congenital mutations in the LCT gene and in adults by reduced LCT gene expression resulting from regulatory element mutations.

Amyloid-beta ($A\beta$)

A 40–42 amino acid peptide produced by proteolytic cleavage of amyloid precursor protein that spontaneously aggregates into insoluble cross-$\beta$-sheet fibrils to form plaques in Alzheimer's disease.

$$PrP^{Sc}$$

The infectious, $\beta$-sheet-rich pathogenic conformation of the prion protein that binds to normal $\alpha$-helix-rich $PrP^C$ and converts it into the disease-causing isoform via an exponential cascade.

Protein Domain

A distinct, semi-independent structural and functional unit within a protein that can maintain its fold and activity even when isolated from the rest of the polypeptide chain.

Glycosylation

A post-translational modification involving the covalent addition of carbohydrate chains to a protein, regulating its folding, conformation, stability, localization, and activity.

Ubiquitination

A post-translational modification in which ubiquitin tags are covalently attached to a target protein to direct it for cellular degradation.

S-Nitrosylation

A post-translational modification that stabilizes proteins, controls gene expression, and serves as an intracellular donor of nitric oxide ($NO$).

Proteolysis

A post-translational modification involving the enzyme-catalyzed hydrolysis of peptide bonds to activate precursor proteins (such as trypsinogen to trypsin) or release specific peptide fragments.