Protein Structure and Function Flashcards

Vocabulary practice flashcards covering protein structures, folding mechanisms, collagen, hemoglobin, myoglobin, and immunoglobulins.

Polypeptide Backbone

The repeating structural backbone sequence of $N-C_\text{α}-C-N-C_\text{α}-C-N-C_\text{α}-C…$ linked by peptide bonds in a protein.

Conformation

The final three-dimensional folded shape of a protein that possesses the lowest possible free energy and maximum stability.

Denaturation

The process of unfolding a protein, manifested by coagulation, caused by heat, pH extremes, or chemical agents such as alcohol, urea, acids, and bases.

$\alpha$-Helix

A regular spiral protein folding pattern formed by hydrogen bonding between every $4\text{th}$ peptide bond ($C=O$ to $N-H$).

$\beta$-Sheet

A regular protein folding pattern where the polypeptide chain folds back on itself like a ribbon, forming a rigid structure bound by hydrogen bonds.

Anti-Parallel $\beta$-Sheet

A type of $\beta$-sheet conformation where adjacent polypeptide segments run in opposite directions relative to one another.

Parallel $\beta$-Sheet

A type of $\beta$-sheet conformation where adjacent polypeptide segments run in the same direction, connected by longer looping sections.

Coiled-Coil Shape

A structural framework formed when $\alpha$-helices coil around each other, commonly found in structural proteins of hair, nails, and skin.

Globular Proteins

Water-soluble proteins with compact, ball-like shapes and irregular surfaces, including enzymes, transport proteins, immunoglobulins, and hormones.

Fibrous Proteins

Water-insoluble structural proteins with long, rod-shaped three-dimensional structures that span long distances in cells, such as collagen and keratin.

Alpha Keratin

A fibrous structural protein constructed from right-handed $\alpha$-helices assembled into coiled coils, protofilaments, and microfilaments.

Collagen

The most abundant protein in the human body (25\text{%} of total protein weight), consisting of three $\alpha$ chains wrapped in a right-handed triple helix.

Collagen Alpha Chain

A left-handed helical polypeptide chain containing $3$ amino acid residues per turn and a repeating tripeptide sequence of Gly-X-Pro or Gly-X-4-Hyp.

Glycine (in Collagen)

The smallest amino acid residue required at the tight inner junction where the three $\alpha$ chains of collagen meet.

Ascorbic Acid

Vitamin C; an essential cofactor for hydroxylase enzymes during the posttranslational modification of proline and lysine in collagen.

Scurvy

A condition characterized by bleeding gums and skin discoloration resulting from fragile collagen synthesis due to vitamin C deficiency.

Osteogenesis Imperfecta

Brittle bone syndrome; a genetic disorder characterized by abnormal bone formation and frequent fractures caused by replacing glycine with a bulkier amino acid.

Ehlers-Danlos Syndrome

A genetic collagen disease characterized by stretchy skin and loose joints due to the substitution of glycine with an amino acid having a larger side chain.

Elastin

A protein with rubber-like properties and random coil structure found in elastic fibers like lungs and blood vessels that recoils after stretching.

Coagulation

The precipitation out of a biochemical solution of denatured protein molecules.

Myoglobin

A single-chain globular protein of $153$ amino acid residues containing $1$ heme group that stores and transports oxygen in muscle tissue.

His E7 and His F8

The distal (His E7) and proximal (His F8) histidine residues in helices E and F of myoglobin that participate directly in oxygen binding.

Hemoglobin

A tetrameric hemoprotein ($2\text{α}$ and $2\text{β}$ chains) in red blood cells that transports oxygen and carbon dioxide cooperatively.

Heme

A metalloporphyrin consisting of a protoporphyrin ring with $4$ pyrroles linked by methine bridges and a central $\text{Fe}^{2+}$ cation bound by $4$ coordination covalent bonds.

Hemoglobin A

The predominant adult hemoglobin form ($\text{HbA}_1$), comprising two $\alpha$ and two $\beta$ globin subunits.

Fetal Hemoglobin

Hb F; a tetrameric hemoglobin consisting of two $\alpha$ and two $\gamma$ subunits that exhibits a higher oxygen affinity than adult hemoglobin.

Hemoglobin S

An abnormal hemoglobin variant associated with sickle cell anemia, caused by a mutation replacing glutamate with valine in the $\beta$-globin chain.

Methemoglobin

An oxidized form of hemoglobin containing $\text{Fe}^{3+}$ (ferric) instead of $\text{Fe}^{2+}$ (ferrous) iron in its heme groups.

Carbonylhemoglobin

HbCO; a hemoglobin complex formed when carbon monoxide binds to $\text{Fe}^{2+}$ with $200$ times higher affinity than oxygen.

Carbaminohemoglobin

A derivative of hemoglobin carrying approximately 23\text{%} of total blood $\text{CO}_2$ bound to the N-terminal amino groups of the T form.

Glycated Hemoglobin

$\text{HbA}_{1c}$; a nonenzymatically glycosylated form of hemoglobin that reflects mean blood glucose levels over the preceding $6\text{--}8\text{ weeks}$.

Bohr Effect

The decrease in hemoglobin's oxygen affinity at lower pH levels, facilitating oxygen unloading in acidic peripheral tissues.

Immunoglobulins

Gamma globulin glycoproteins (antibodies) synthesized by plasma cells, composed of two heavy chains and two light chains connected by disulfide bonds.

Immunoglobulin G

IgG; a monomeric antibody that serves as the major circulating immunoglobulin in blood and tissue fluids, capable of crossing the placenta and acting as an opsonin.

Immunoglobulin D

IgD; a monomeric antibody attached to the membrane of B lymphocytes that aids in B cell activation.

Immunoglobulin A

IgA; a dimeric secretory antibody present in tears, saliva, colostrum, and mucosal secretions that inhibits bacterial glycolytic metabolism.

Immunoglobulin E

IgE; a monomeric antibody in blood and lymph involved in mediating allergic reactions and defense against parasites.

Immunoglobulin M

IgM; a pentameric antibody that is the first class produced during a primary immune response, strongly fixing complement and attacking foreign antigens.

Sickle-Cell Trait

A heterozygous condition where an individual inherits one normal and one mutant gene, producing both HbA and HbS without experiencing severe clinical symptoms.

Renaturation

The refolding process in which a denatured protein regains its native conformation and functional biological activity after denaturing chemicals are removed.