Amino Acids, Peptides, and Proteins

Vocabulary practice flashcards covering human biochemistry concepts including amino acid properties, protein structure levels, hemoglobin function, and related pathologies.

Peptides

Straight-chain molecules composed of amino acids joined by peptide bonds that contain fewer than 40 amino acids.

Proteins

Molecules composed of amino acid chains held together by peptide bonds that contain 40 or more amino acids.

Zwitterions

Bipolar ions with no overall charge created by internal reversible ionization reactions of the amine group ($NH_2 + H^+ \rightleftharpoons NH_3^+$) and carboxylic acid group ($COOH \rightleftharpoons COO^- + H^+$).

Nonpolar Amino Acids

Nine hydrophobic neutral amino acids (L-alanine, L-valine, L-leucine, L-isoleucine, L-proline, L-phenylalanine, L-tryptophan, L-tyrosine, L-methionine) located in the interior of most proteins.

Polar Neutral Amino Acids

Six hydrophilic amino acids (glycine, L-serine, L-threonine, L-cysteine, L-asparagine, L-glutamine) that attract water and are located on the surface of most proteins.

Polar Acidic Amino Acids

Anionic amino acids (L-aspartic acid and L-glutamic acid) containing two $COO^-$ groups and one $NH_3^+$ group, with an extra $COO^-$ located in the R group.

Polar Basic Amino Acids

Cationic amino acids (L-lysine, L-arginine, L-histidine) containing two $NH_3^+$ groups and one $COO^-$ group, with an extra $NH_3^+$ located in the R group.

Isoelectric Point

The specific pH value at which an amino acid predominantly exists in solution as a zwitterion with net zero charge.

Peptide Bond

A covalent amide linkage formed when the carboxylic acid group of one amino acid reacts with the amine group of another amino acid, releasing $H_2O$.

Globular Proteins

Spherical-shaped proteins (such as insulin, hemoglobin, and transferrin) that typically form suspensions in blood or intracellular fluid.

Fibrous Proteins

Strand- or sheet-shaped proteins (such as keratin, collagen, elastin, and fibrin) that intertwine to form strong, solid fibers in tissues.

Conjugated Proteins

Proteins that consist of a protein portion called an apoprotein bound to a nonprotein portion called a prosthetic group.

Apoprotein

The protein component of a conjugated protein molecule.

Prosthetic Group

The nonprotein component attached to a conjugated protein, such as lipids in lipoproteins, sugars in glycoproteins, or metals in metalloproteins.

Primary Level of Protein Structure

The specific sequence and order of amino acids linked together by covalent peptide bonds, determined by genetic code (DNA).

Secondary Level of Protein Structure

Shorter 3D structural segments within a larger protein (such as $\alpha$-helices and $\beta$-pleated sheets) formed and stabilized by hydrogen bonds between amino acids.

Tertiary Level of Protein Structure

The overall 3D structural conformation of a single amino acid chain, held together by interactions exclusively between side chain functional groups (disulfide bonds, salt bridges, hydrogen bonds, hydrophobic interactions).

Quaternary Level of Protein Structure

A protein structure consisting of two or more amino acid chains (subunits or monomers) held together by hydrogen and disulfide bonds.

Denaturation

A change in a protein's conformation, physical properties, or biological functionality resulting from the disruption of hydrogen bonds, while peptide and disulfide bonds remain intact.

Prions

Misfolded proteins that induce damage in normal proteins, causing them to aggregate into insoluble plaques in brain tissue and lead to fatal neurodegenerative diseases.

Collagen

A fibrous protein composed of three separate amino acid chains wrapped in a triple-helix conformation rich in L-proline and L-lysine that yields gelatin when denatured.

Heme

The prosthetic group in myoglobin and hemoglobin consisting of four pyrrole rings bonded into a porphyrin ring with a central ferrous iron ($Fe^{2+}$) atom.

Pyrrole Ring

A five-membered heterocyclic structural unit containing nitrogen, four of which bind together to form the cyclic tetrapyrrole porphyrin ring of heme.

Oxygen Cooperativity

An allosteric modification where binding of one $O_2$ molecule to hemoglobin changes its conformation (T-form to R-form), increasing affinity for subsequent $O_2$ molecules.

Bohr Effect

A $CO_2$ transport mechanism in non-lung tissues where $CO_2$ forms $H_2CO_3$, ionizes into $H^+$ and $HCO_3^-$, and $H^+$ binds deoxygenated hemoglobin ($Hgb\text{-}H$), releasing $O_2$.

Chloride Shift

An anion exchange process where chloride ions ($Cl^-$) enter the red blood cell from blood plasma to replace exiting bicarbonate ions ($HCO_3^-$), maintaining electrical neutrality.

2,3-Bisphosphoglycerate (2,3-BPG)

A glycolysis byproduct produced in RBCs that promotes oxygen release from $Hgb\text{-}O_2$ to peripheral tissues.

Sickle Cell Anemia

A genetic condition where L-valine replaces L-glutamic acid at the 6th position of the $\beta$-chain, causing hemoglobin to aggregate in the deoxy state and distort red blood cells.

Glycosylated Hemoglobin (HgbA1c)

A glycated form of hemoglobin produced when glucose binds to L-lysine residues, measured to assess blood glucose concentration over preceding weeks in diabetes management.