BIOC 503 - Water Lecture 1

UV light

life evolved in water due to its protection from __

70-80

organisms are usually ___ % water

aqueous

most of the chemical rxns are happening in ___ environments

proteins, nucleic acids, membrane

water is critical determinant of structure and function of ___, ____, and ___.

Structure of the water molecule

• 8 electrons around oxygen atom as per octet rule

• all electrons in sp3 orbitals

• 2 covalent bonds to hydrogen atoms

• 2 lone pairs

• bent (distorted tetrahedron) geometry

• net dipole moment due to oxygen electronegativity

• both electron donor and acceptor due to dipole moment

Hydrogen bonds

___ = strong dipole-dipole interactions arising between covalently bound hydrogen and lone pairs of electrons

oxygen, nitrogen, sulfur

elements usually involved in hydrogen bonding

linear

hydrogen bonds are the strongest when the bonded molecules allow for a ___ pattern

• aka ideally atoms are in a line

BP, MP, surface tension

hydrogen bonds are the reason behind water’s high ___, ___, and ____.

weak

H bonds between neighboring molecules are ___ ( kJ/mol)

Importance of H bonds

• source of water unique properties

• structure and function of proteins/DNA/polysaccharides

• bonding of substrates to enzyme & hormones to receptors

• matching mRNA and tRNA

hexagonal

most common ice form is ___, an organized lattice with low entropy

equidistant

hexagonal ice maximizes hydrogen bonds to water molecule ratio, forcing the water molecules to be ___ making ice less dense than liquid water and floats

• 4 H bonds per H2O molecule

polar

water is a GOOD solvent for __ molecules

• amino acids, peptides, small alcohols, carbohydrates

nonpolar

water is a poor solvent for ___ molecules

• __ gases, aromatic moieties, aliphatic chains

noncovalent

___ interactions do not involve sharing a pair of electrons

ionic interactions

aka coulombic interactions

electrostatic interactions between permanently charged species or between ions with permanent dipole

dipole interactions

electrostatic interactions between uncharged but polar molecules

Van Der Waals interactions

weak interactions between all atoms, regardless of polarity

can be attractive (dispersive force) or repulsive (steric force)

Hydrophobic effect

__ = association or interaction of nonpolar molecules or components of molecules in the aqueous solution

complex phenomenon associated with the ordering of water molecules around nonpolar substances

dielectric constant

dissolving salt involves breaking ionic interactions, water has a high ___ which reduces attraction between oppositely charged ions in salt crystal

• almost no attraction over 40 nm

lower

when dissolving salt, strong electrostatic interactions between solvated ions and water molecules ___ the total energy of the system

increases

entropy ___ as ordered crystal lattice is dissolved

hydration shell

water dissolves salt by forming a ___ around their component ions to partially neutralized ionic charges

London force, steric repulsion

2 components of van der Waals interactions

• attractive force (___) which depends on the polarizability and dominates at longer distances (0.4-0.7 nm)

• repulsive force (___) which depends on the size of the atoms and dominates at short distances

contact distance

minimum energy distance for van der Waals interactions`

reversible

van der Waals interactions are weak, easily broken, and ___ as well as universal

importance of van der Waals interactions

• determine steric complementarity

• stabilized biological macromolecules (stacking DNA)

• facilitates bonding of polarizable ligands

hydrophobic effect is one of main factors behind

• protein folding

• protein-protein association

• formation of lipid micelles

• binding of steroid hormones to their receptors

unfavorable

water surrounding nonpolar solutes has lower entropy

lower entropy is thermodynamically ___ thus hydrophobic solutes have low solubility

amphipathic

having both hydrophilic and hydrophobic parts

aggregate

nonpolar portions of the amphipathic molecule ___ so that fewer water molecules are ordered and entropy can increase/not decrease as much

micelles

with high enough concentration of amphipathic molecules, ___ formation is possible

hydrophobic

binding sites in enzymes and receptors are often ___

• binds to ___ ligands which displace the water molecules and increase entropy of system

multiple forces

interactions between enzymes and substrates are NEVER purely because of hydrophobic effect as it says nothing about how the substrate should be positioned.

Position of substrate determined by H bonds and ionic interactions

AKA __ are involved in binding

colligative properties

do not depend on the nature of the solute, just the concentration

• BP, MP, osmolarity

Non colligative properties

depends on the chemical nature of solute

• viscosity, surface tension, taste, color

high to low

water moves from ___ water concentration

• aka from low solute concentration to high solute concentration to dilute it

osmotic pressure

force necessary to resist natural water movement/diffusion

• influenced by concentration of each solute in solution

• dissociated components of a solute individually influence it

isotonic

in ___ solution = no net water movement

hypertonic

in ___ solution = water moves out, aka high concentration of solute OUTSIDE the cell, cell shrinks

hypotonic

in ___ solution = water moves into the cell, aka high solute concentration INSIDE the cell, and cells bursts