biochem - 1 - introduction, water, pH, and buffers

Introduction, Water, pH, Buffers

what is a covalent bond?

hold atoms together to form mlcs

what is a non-covalent bond?

weak chemical forces that maintain biological structure and determine molecular interactions

what are the four non-covalent bonds?

• hydrogen bonds

• ionic interactions:

• hydrophobic interactions:

• van der waals interactions:

what is a hydrogen bond?

forms between a hydrogen atom, covalently bonded to an oxygen or nitrogen, and a second oxygen or nitrogen

what are ionic interactions?

the result of attractive forces between oppositely charged groups, such as negative carboxyl groups and positive amino acid groups

what are hydrophobic interactions?

interactions due to the strong tendency of water to exclude non-polar groups or molecules, because water molecules prefer the stronger interactions between water molecules

what do van der waals interactions result from?

electron cloud fluctuations

where do van der waals interactions occur between?

positively charged nuclei and negatively charged electrons of nearby atoms (attractive forces)

what are the properties of water?

• high BP

• high MP

• high heat of vaporization

• high surface tension

what properties of water result in its unusual properties?

• polar

• hydrogen bonds

how many hydrogen bonds does a water molecule average?

3.4 hydrogen bonds

ice has a _ density compared to liquid water

low

how many hydrogen bonds does a water molecule form in ice?

4

what is the average lifetime of a H-bond between two H2O molecules?

9.5 picoseconds

how many seconds is 9.5 picoseconds?

9.5 × 10^-12 s

what makes water a good solvent?

• hydration shells - water (polar) surrounds ions and diminishes their charges

• hydrophobic interactions - non-polar solute molecules in water experience a net attraction for one another called hydrophobic interactions; a clathrate (cage-like) structure is formed by water molecules surrounding a hydrophobic solute

• hydrogen bonds - form between water and polar solutes

• micelles - amphiphilic (or amphipathic) molecules contain both strongly polar and strongly non-polar groups, such as fatty acids which have charged carboxyl groups and ling hydrophobic chains. these form clusters in aqueous solutions called micelles.

describe the dielectric constant (D) of water

high due to the partial positive and negative charges on the molecule (resulting from its polarity), resulting in ions with diminished attraction for each other. (hydration shells)

what are colligative properties?

• properties which depend on the number of solute particles per unit volume of solvent

• do not depend on the chemical nature of the solute

what are examples of colligative properties?

• osmotic pressure effects

• freezing point depression

• boiling point elevation

• vapor pressure lowering

what is a consequence of high osmotic pressure?

swelling and rupture of the cell (high concentrations of dissolved solutes within the cell)

what is pH?

a measure of the hydrogen ion concentration in an aqueous solution

what equation defines pH?

pH = - log[H+]

or

[H+] = 10^-pH

what are the two most important buffer systems of cells and blood?

• phosphate buffer system

• carbonate buffer system

what does the phosphate system do?

buffers the intracellular fluid of cells at physiological pH

• the dihydrogen phosphate ion neutralizes excess hydroxide ion: H2PO4^- + OH^- → HPO4^2- + H2O

• the monohydrogen phosphate ion neutralizes hydrogen ion: HPO4^2- + H+ → H2PO4^-

what does the phosphate system consist of?

• dihydrogen phosphate ion: H2PO4^-

• monohydrogen phosphate ion: H2PO4²-

what is important about the phosphate ion that is formed by neutralizing the hydroxide ion?

it is the other phosphate ion of the buffer system (in the second reaction)

what is the carbonate system realevant for?

blood plasma - the carbonate system is the important buffer system of blood plasma

what are the components of the carbonate system?

• bicarbonate ion: HCO3^-

• carbonic acid H2CO3

what are the steps of the carbonate system?

• the bicarbonate ion neutralizes excess hydrogen ion in the blood: HCO3- + H+ → H2CO3

  • if a large excess of acid and therefore hydrogen ion is found in the blood, perhaps due to some disease condition, a large amount of carbonic acid will be produced

  • excess carbonic acid is eliminated because carbonic acid is unstable and forms carbon dioxide and water: H2CO3 → CO2 + H2O

  • The CO2 is removed from the body through the lungs by hyperventilation

• carbonic acid neutralizes hydroxide ion: H2CO3 + OH- → HCO3^- + H2O