Quiz 2 Flashcards
Covalent bonds
Hold atoms together so that molecules are formed
Weak forces
Create interactions that are constantly forming and breaking under physiological conditions
1. Van der waals (closest fit )
2. Hydrogen bonding ( short and straight )
3. Ionic interactions ( opposite charges )
Molecular recognition
Is mediated by weak chemical forces
for example: hydrogen bonds forms double bonded DNA
Restricts organism to a narrow range of environmental conditions
Weak forces.
- changes in its temperature pressure or pH can easily disrupt weak forces
Van der waals
Is enhanced in molecules that are structurally complementary
Important hydrogen bonds
Straight short (~3A)
[ higher in energy ,harder to break thus bond angle important for directionality ]
H-bond donors
Electronegative atoms O and N attached to H
H-bond acceptors
The electronegative atoms O and N
Ionic bonds
- unlike h bonds, they do not require specific angles
- weak interactions contribute to stability of proteins
Water molecules
- polar
- high dielectric constant : solvates polar groups well [ attraction of charges and partial charges are responsible ]
- forms H bonds with polar, uncharged solutes
Ice
- water molecules that are hydrogen bonded in a crystalline array
- 4 H bonds
Attractive forces acting on biological molecules
- ionic interactions
- hydrogen bonds
- van der waals interactions
Non polar substances
- do not dissolve in water
Hydrophobic effect [1]
- exclusion of non polar groups as a way to maximize entropy of water molecules
- non polar molecules aggregate together to free many molecules of water, vastly increasing entropy
[increased freedom of water molecules by decreasing surface area of the non polar solute]
Amphiphilic
- form micelles or bilayers that hide their hydrophobic groups while exposing their hydrophilic groups to water
Polar heads and non polar tails
Osmosis
Solvent molecules diffuse across membranes which are permeable to them from regions of higher concentration to regions of lower concentrations
- diffusion of solvents
Dialysis
Solute diffuse across a semipermeable membrane from regions of higher concentrations to regions of lower concentration
- diffusion of solutes
Important for water
- Bent structure is key, makes it polar
- Non- tetrahedral bond angles define directionality of interactions
- H- bond donors and H-bond acceptors
- Able to form 4 H bonds per water molecule [ice forms 4]
Liquid water
2-3 H bonds per water molecule at any given time
H bonds of liquid water are too transient to form all 4 at once
Ions
Carry around a hydration shell of water molecules
[always hydrated in water]
Water H bonds with
- hydroxyl group
- carbonyl group
- carboxyl group
- amino group
hydrophobic effect
- non polar molecules aggregate together to free many molecules of water vastly INCREASING ENTROPY[favored] , without losing any of the enthalpy
Water-water H bonds are enthalpicaly favorable (hydrophobic effect)
The increase in the order of water is even more strongly entropically opposed
Dissociation constant
10^-14
- varies with strength of an acid
