Water: The Solvent for Biochemical Reactions

Flashcards on Water and Biochemical Reactions

Water (H2O)

The most abundant molecule on Earth's surface, constituting about 75% of the Earth's surface and essential for life.

Universal Solvent

Water is often referred to as the universal solvent because many substances dissolve in it.

Heavy Water

Water in which the hydrogen atoms are replaced by heavier isotopes, deuterium (2H) and tritium (3H).

Electronegativity

The tendency of an atom to attract electrons to itself in a chemical bond.

Polar Bond

A covalent bond in which electrons are unequally shared between atoms due to differences in electronegativity.

Hydrophilic

Describes molecules or substances that are highly polar or partially polar and tend to dissolve in water (water-loving).

Hydrophobic

Describes non-polar molecules or substances that do not readily dissolve in water (water-fearing).

Amphipathic

Describes molecules that have both polar and non-polar regions (both water-loving and water-fearing properties).

Van der Waals forces

Small, short-lived dipole charges that tend to hold non-polar molecules together.

Hydrogen Bond

Electrical attraction between water molecules, due to the dipole pulls, individual molecules closer together and making it more difficult to separate the molecules

Hydrogen-bond donor

The group comprising the electronegative atom that is covalently bonded to hydrogen.

Hydrogen-bond acceptor

The electronegative atom that contributes the unshared pair of electrons to the interaction.

Acid (biological definition)

Any molecule that can donate a proton (hydrogen ion).

Base (biological definition)

Any molecule that accepts a proton.

Dissociation Constant (Ka)

A measure of the strength of an acid, indicating how well it can dissociate its hydrogen ions.

pH

A quantity used to express the concentration of hydrogen ions in a solution; pH = -log10[H+].

pKa

A quantity defined by analogy with pH as pKa = -log10Ka, and another numerical measure of acid strength; the smaller its value, the stronger the acid.

Buffer

A solution whose pH resists change upon the addition of either more acid or more base; consists of a weak acid and its conjugate base.

Titration

An experiment in which measured amounts of acid (or base) are added to measured amounts of base (or acid).

Equivalence point

The point in an acid-base titration at which enough acid has been added to exactly neutralize the base (or vice versa).

Henderson-Hasselbalch Equation

An equation that relates the pH of a solution to the pKa of a weak acid and the concentrations of the weak acid and its conjugate base.