Water

Predominant chemical component of living organisms Physical properties: Ability to solvate a wide range of organic & inorganic molecules Due to strong dipolar structure & high dielectric constant Dipolar structure Exceptional capacity for forming H bonds

This favors the self-association of water molecules into ordered arrays Influences the physical properties of water Accounts for the waters high viscosity, surface tension, & boiling point

Its rupture in liquid water require 4.5kcal/mol Enables water to dissolve in many organic biomolecules that contain functional groups w/c participate in H bonding

O2 atoms of aldehydes

ketones

amides Excellent nucleophile

Electron-rich molecules Attack electrophiles (electron-poor) Ex. Carbonyl carbons in amides Esters Aldehydes Ketones Phosphorus atoms of phosphoesters Nucleophilic attack by water generally results hydrolysis Water: Due to the 2 lone pairs of sp3 electrons that bear a partial negative charge Other examples: Oxygen atoms of phosphates, alcohols, & carboxylic acids Sulfur of thiols Nitrogen of amines Imidazole ring of histidine Can be both reactant or product in many rxns Has high dielectric constant = 78.5

It greatly decreases the force of attraction bet. charged and polar species relative to water-free environments with lower DC Can act both acid and as a base Water balance regulation in the body: Hypothalamus Thirst ADH Water retention/excretion by kidneys Evaporative loss Each molecule of water in a liquid water associates through H bonds with 3.5 others

Relatively weak Transient Half life about a millisecond Its interaction with biomolecules influences the latters structure Stabilized by covalent & noncovalent bonds Covalent sharing of e- Noncovalent

Ionic bond Electrostatic forces help shape biomolecular structure Forms salt bridges Hydrophobic interactions Tendency of nonpolar compounds to self - associate with aqueous environment

Arises from the need to

minimize energetically

unfavorable interactions

bet. non polar groups &

water

Ex. Oil & water (their optimal free energy is a mixture of both maximal enthalpy & minimum entropy) H-bonds Van der Waals forces (dipole-dipole, LDF) Attractions bet transient dipoles generated by the rapid movement of electrons on all neutral atoms Weaker than H bond Potentially extremely numerous Decrease as the 6th power of the distance separating atoms Most are amphipathic

Hydrophilic + hydrophobic As a result, biomolecules fold in position Ex. Phosphobilipid layer Their molecules exhibit a slight but important tendency to dissociate Can act both as an acid or base Other water molecules that exist in clusters (continuously combine to form these molecules) H3O+ H5O2+ H7o3+ Individual H+ or O2 cannot be stated to be present as an ion or part of a water molecule 1 g of H2O = 3.46 x 1022 molecules 1.8 x 10 -9 prob. Of existing H ion in water molecule 1.8 x 10 9 - prob. Of H ion being part of water moleculepH of ECF 7.35-7.45 Verification of disturbances: pH of arterial blood pressure CO2 content of venous blood pH < 7.45 ACIDOSIS pH > 7.35 - ALKALOSIS