Flashcards in Chapter 2 - Water, Molecular Interactions, Acid-Base Deck (22):
Number of hydrogen bonds possible per water molecule
4 (2 bonding to Hs and 2 bonding to the lone pairs of O)
Lifetime of hydrogen bond?
1-20 ps (10^-12s)
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)
Strength of pi stacking (aromatic ring stacking)
0.4 - 4 kJ/mol
Strength of Van der Waals interactions (weak but many)
Strength of hydrogen bond (O-H⚫️⚫️⚫️⚫️⚫️O-C)
Strength of electrostatic (pH effects, opposites attract, likes repel)
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)
Both hydrophilic (likes water, polar or charged) and hydrophobic (dislikes water, nonpolar) is called...
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
Consists of an aqueous solution of a weak acid (proton donor) and its conjugate base (proton acceptor)
Tend to resist changes in pH, near the buffering-weak-acid pKa, when small amounts of acid (H+) or base (OH-) are added
pH = pKa + log ( [A-]/[HA] )
Henderson - Hasselbalch Equation
A digestive enzyme secreted into gastric juice, which has a pH of ~1.5
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