Chapter 2 - Water, Molecular Interactions, Acid-Base Flashcards
Lifetime of hydrogen bond?
1-20 ps (10^-12s)
Number of hydrogen bonds possible per water molecule
4 (2 bonding to Hs and 2 bonding to the lone pairs of O)
Hydrogen bond donors
N-H, O-H, not C-H
Hydrogen bond acceptors
N: and O:
Hydrogen bond is stronger when 3 atoms…
Involved lie in a line
Difference in the energy between a functional folded protein and an unfolded protein
10kJ / mol
Strength of hydrophobic interactions (displacement of water)
0.4-4 kJ/mol
Strength of pi stacking (aromatic ring stacking)
0.4 - 4 kJ/mol
Strength of Van der Waals interactions (weak but many)
0.4-4 kJ/mol
Strength of hydrogen bond (O-H⚫️⚫️⚫️⚫️⚫️O-C)
4-40 kJ/mol
Strength of electrostatic (pH effects, opposites attract, likes repel)
4-40 kJ/mol
Strength of salt bridge (hydrogen bonding plus electrostatic)
E.g. Carboxylate amino acid side chain (Asp, Glu) to basic amino acid side chain (Arg, Lys)
40-400 kJ/mol
Both hydrophilic (likes water, polar or charged) and hydrophobic (dislikes water, nonpolar) is called…
Amphipathic
What’s the equilibrium constant (Keq) for water dissociation at 25*C?
1.8 x 10 ^ -16 M
Ion product of water at 25*C?
Kw = [H+] [OH-] = (1.8 x 10 ^ -16 M)(55.5 M) = 1.0 x 10^-14 M^2
Bronsted Acid?
H+ donor
Consists of an aqueous solution of a weak acid (proton donor) and its conjugate base (proton acceptor)
Buffers
Tend to resist changes in pH, near the buffering-weak-acid pKa, when small amounts of acid (H+) or base (OH-) are added
Buffers
pH = pKa + log ( [A-]/[HA] )
Henderson - Hasselbalch Equation
A digestive enzyme secreted into gastric juice, which has a pH of ~1.5
Pepsin
Digestive enzyme that acts in the small intestine, and has a pH optimum that matches the neutral pH in the lumen of the small intestine
Trypsin
Hydrolytic enzyme thought to aid in bone mineralization
Alkaline phosphates of bone tissues
