Biochemistry: Protein Structure, Dynamics, and Enzyme Kinetics Vocabulary Flashcards

Comprehensive vocabulary flashcards covering key terms and definitions in protein structure, folding dynamics, oxygen binding, structural techniques, amino acids, and enzyme kinetics.

Native Conformation

The major three-dimensional conformation of a protein that possesses full biological activity.

Primary Structure

The specific linear sequence of amino acids in a polypeptide chain that determines its overall three-dimensional conformation and biological function.

Alpha-Helix

A helical secondary structure motif in proteins stabilized by intrachain hydrogen bonds between the carbonyl oxygen of one amino acid residue and the amide nitrogen of another residue four positions along the backbone.

Beta-Sheet

A secondary protein structure composed of extended polypeptide strands arranged side by side, stabilized by interstrand hydrogen bonding between backbone peptide bonds.

Beta-Bulge

A common, non-repetitive irregular secondary structure motif found in antiparallel $\beta$-sheets where an extra residue causes a localized structural disruption.

Reverse Turns

Protein secondary structure elements where the polypeptide chain abruptly changes direction, commonly containing glycine due to minimal steric hindrance and proline due to its rigid cyclic structure.

Supersecondary Structures

Recurring geometric combinations of secondary structure elements, such as the $\beta \frac{}{} \beta$ unit, $\beta \text{-meander}$, and Greek key pattern.

Fibrous Proteins

Water-insoluble, mechanically strong proteins organized parallel along a single axis into long fibers or large sheets that fulfill structural roles in organisms.

Globular Proteins

Compact, spherical, water-soluble proteins folded so that polar side chains reside on the exterior surface while nonpolar side chains are buried in the interior.

Collagen Triple Helix

A structural motif composed of three coiled polypeptide chains with repeating $\text{X-Pro-Gly}$ or $\text{X-Hyp-Gly}$ sequences that become covalently cross-linked between lysine and histidine residues with age.

Zwitterion

A dipolar molecule containing both positively and negatively charged functional groups with an overall net electrical charge of zero at neutral $\text{pH}$.

Isoelectric Point

The specific $\text{pH}$ value at which a majority of molecules of a compound carry no net electrical charge.

Peptide Bond

A covalent amide bond formed between the $\text{a-carboxyl}$ group of one amino acid and the $\text{a-amino}$ group of another via a condensation reaction, possessing partial double-bond character.

Myoglobin

A monomeric oxygen-binding globular protein present in muscle tissue that contains a single heme group and exhibits a hyperbolic oxygen-binding curve.

Hemoglobin

A tetrameric protein consisting of two $\text{a}$ chains and two $\text{b}$ chains ($\text{a}_2 \text{b}_2$) that transports oxygen in red blood cells and exhibits a sigmoidal, cooperative oxygen-binding curve.

Heme Group

An iron-containing prosthetic group consisting of an iron(II) ion ($\text{Fe}^{2+}$) bound within an organic protoporphyrin IX ring made of four pyrrole rings.

Bohr Effect

The phenomenon in which increased concentrations of $\text{H}^+$ (lower $\text{pH}$) and $\text{CO}_2$ decrease hemoglobin's binding affinity for oxygen, promoting oxygen release in metabolizing tissues.

2,3-Bisphosphoglycerate

An allosteric effector that binds in the central cavity of deoxyhemoglobin, stabilizing its unoxygenated state and lowering its binding affinity for oxygen.

Denaturation

The process by which a protein loses its native three-dimensional structure and biological activity due to environmental stress such as heat, extreme $\text{pH}$, detergents, urea, or guanidine hydrochloride.

Molecular Chaperones

Specialized helper proteins, such as $\text{Hsp70}$ and $\text{Hsp60}$, that assist in the correct and timely folding of polypeptide chains and prevent undesirable protein aggregation.

Alpha-Hemoglobin Stabilizing Protein

A specific chaperone protein that binds free $\text{a-globin}$ chains to prevent their precipitation into inclusion bodies prior to assembly with $\text{b-globin}$ chains.

X-ray Crystallography

A structural biology technique in which a protein crystal is exposed to an X-ray beam, producing a diffraction pattern analyzed via Fourier series to determine 3D atomic coordinates.

Nuclear Magnetic Resonance Spectroscopy

A structural biology technique capable of determining the three-dimensional structures of biomolecules directly in aqueous solution by measuring nuclear spin interactions.

Activation Energy

The energy barrier representing the difference in free energy between reactants and the transition state that must be overcome for a chemical reaction to occur.

Active Site

The small, restricted region on an enzyme surface where substrate molecules bind via noncovalent interactions and undergo catalytic transformation.

Fischer Lock-and-Key Mechanism

A model of enzyme-substrate interaction proposing that the enzyme active site is rigid and fixed in shape, precisely complementary to the substrate prior to binding.

Koshland Induced-Fit Mechanism

A model of enzyme binding in which the active site undergoes a conformational change upon substrate binding to adapt its shape to the substrate.

Michaelis Constant

The substrate concentration at which the initial reaction velocity ($\text{V}_{\text{init}}$ ) reaches half of its maximum value ($\frac{\text{V}_{\text{max}}}{2}$), serving as a measure of enzyme-substrate binding affinity.

Maximum Velocity

The maximum reaction rate achieved when an enzyme active site is completely saturated with substrate ($[\text{ES}] = [\text{E}]_{\text{T}}$).

Turnover Number

The maximum number of moles of substrate converted into product per mole of enzyme active site per unit time when the enzyme is fully saturated.

Lineweaver-Burk Plot

A double-reciprocal plot of $\frac{1}{\text{V}}$ versus $\frac{1}{[\text{S}]}$ that linearizes the Michaelis-Menten equation, yielding a y-intercept of $\frac{1}{\text{V}_{\text{max}}}$ and an x-intercept of $-\frac{1}{\text{K}_{\text{M}}}$.

Competitive Inhibitor

A molecule that closely resembles the natural substrate and competes for binding at the active site, increasing the apparent $\text{K}_{\text{M}}$ without altering $\text{V}_{\text{max}}$.

Noncompetitive Inhibitor

An inhibitor that binds to an allosteric site on both free enzyme and enzyme-substrate complex with equal affinity, reducing $\text{V}_{\text{max}}$ without altering $\text{K}_{\text{M}}$.

Uncompetitive Inhibitor

An inhibitor that binds exclusively to the enzyme-substrate complex ($\text{ES}$) and not to the free enzyme, causing a decrease in both $\text{V}_{\text{max}}$ and $\text{K}_{\text{M}}$.

Mixed Inhibitor

An inhibitor that binds to both free enzyme and enzyme-substrate complex with unequal affinities, altering both $\text{V}_{\text{max}}$ and $\text{K}_{\text{M}}$.