Biochemistry Flashcards: Water, Noncovalent Interactions, pH, and Buffer Systems

Vocabulary practice flashcards covering water structure, noncovalent interactions, hydrophobic effect, colligative properties, ionization, pH, pKa, and buffer systems based on lecture notes.

Intracellular fluid (ICF)

The fluid situated within cells, comprising a major portion of total body water.

Interstitial fluid (IF)

The portion of extracellular fluid (ECF) present between cells through which materials exchange with blood plasma.

Electronegativity

The tendency of an atom to attract bonding electrons toward its nucleus, as seen in oxygen pulling shared electrons away from hydrogen in a water molecule.

Hydrogen bond

A weak electrostatic interaction between an uncharged polar proton donor (acid) covalently bonded to an electronegative atom and a proton acceptor (base) containing a lone pair.

Acid

Any chemical entity or molecule that acts as a proton donor.

Base

Any chemical entity or molecule that acts as a proton acceptor.

Amphipathic compound

A molecule containing both polar (hydrophilic) and nonpolar (hydrophobic) regions.

Hydrophobic effect

The association or folding of nonpolar molecules in aqueous solution, driven by the thermodynamic favorability of releasing ordered water molecules to maximize system entropy.

Entropy

A thermodynamic measure of disorder or randomness in a system, where higher entropy is favored.

van der Waals interactions

Weak, noncovalent electrostatic forces occurring between any two atoms in close proximity, consisting of attractive dispersion forces and short-range steric repulsion forces.

Colligative properties

Physical properties of a solution—including boiling point, melting point, and osmolarity—that depend solely on the concentration of solute particles rather than their chemical identity.

Noncolligative properties

Solution properties—such as viscosity, surface tension, taste, and color—that depend directly on the specific chemical nature of the solute.

Isotonic environment

A solution state where extracellular solute concentration equals intracellular solute concentration, resulting in no net movement of water across the cell membrane.

Hypertonic environment

A solution state where extracellular solute concentration is higher than inside the cell, causing water to exit the cell and leading to cell shrinkage.

Hypotonic environment

A solution state where extracellular solute concentration is lower than inside the cell, causing water to rush into the cell and leading to osmotic swelling and potential cell bursting.

Conjugate base

The deprotonated species formed when an acid donates a proton, containing one less proton than its corresponding acid.

Conjugate acid

The species formed when a base accepts a proton, containing one more proton than its corresponding base.

Ionic product of water ($K_w$)

The equilibrium constant product of the molar concentrations of $H^+$ and $OH^-$ in water, equal to $1 \times 10^{-14}\text{ M}^2$ at $25\text{ }^\text{o}\text{C}$.

pH

The negative logarithm of the hydrogen ion molar concentration, mathematically expressed as $\text{pH} = -\text{log}([H^+])$.

Polyprotic acid

An acid capable of donating more than one proton during ionization, possessing multiple acid dissociation constants ($K_a$) and $p K_a$ values.

Acid dissociation constant ($K_a$)

An equilibrium constant that quantifies the extent of dissociation and relative strength of an acid in aqueous solution.

pKa

The negative logarithm of the acid dissociation constant ($p K_a = -\text{log}(K_a)$), where a smaller value indicates a stronger acid with a lower affinity for its proton.

Buffer

A mixture of a weak acid and its conjugate base that resists changes in $\text{pH}$ upon the addition of small amounts of acid or base.

Henderson-Hasselbalch equation

A derived equation relating buffer $\text{pH}$, $p K_a$, and the ratio of conjugate base to weak acid concentration: $\text{pH} = p K_a + \text{log}\frac{[A^-]}{[HA]}$.

Bicarbonate buffer system

A vital physiological blood plasma buffer system operating near $\text{pH} = 7.4$, regulated by an equilibrium between gaseous $\text{CO}_2$, dissolved $\text{CO}_2$, carbonic acid ($\text{H}_2\text{CO}_3$), and bicarbonate ions ($\text{HCO}_3^-$).