Ch. 2 - Water, pH, acids, bases, buffers Flashcards
Water can serve as both
Hydrogen bond donor and acceptor
Hydrogen bonds are strong dipole-dipole interactions that arise between
A covalently bonded hydrogen and lone pair of electrons
Typically N or O
H bonds are strongest when the bonded molecules allow for _____ bonding patterns
Linear
Up to ___ H bonds per water molecule
Four
Hydrogen bonding in water is
Cooperative
Hydrogen bonds between neighboring molecules are
Weak relativize to the H-O covalent bonds
Importance of hydrogen bonds
Structure and function of proteins, DNA, polysaccharides
Bonding of substrates to enzymes
Binding of hormones to receptors
Matching of mRNA to tRNA
“Significance of H bond is greater than any more other structural feature”
Linus Pauling
Hexagonal I’ve contains _____ hydrogen bonds
Ps. Also low entropy bc organized lattice
Maximal
Water bound to ____ is essential for their function
Proteins
Water is a _____ solvent for charges and polar substances
Ex)
Amino acids and peptides
Small alcohols
Carbohydrates
Good
Water is a _____ solvent for non polar substances
Ex)
No polar gases
Aromatic moieties
Aliphatic chains
Poor
Noncovalent interactions do ____ involve sharing a pair of electrons
Not
Electrostatic interactions between PERMANENTLY charged species, or between the ion and permanent dipole
Ionic interactions
Electrostatic interactions between uncharged but POLAR molecules
Dipole interactions
Van der waals interactions
Weak interactions between all atoms
Attractive (dispersion)
Repulsive (steric)
Hydrophobic effect
Complex phenomenon associated with the ordering of water molecules around non polar substances
Attractive force
Which depends on the polarizability (very weak)
Dominates at longer distances
London dispersion
Repulsive force
Which depends on the size of atoms
Dominates at very short distances
Steric Repulsion
Determines steric complementarity.
Stabilizes biological macro molecules. (Stacking in DNA)
Facilitates binding off polarizable ligands.
Van der Waals Interactions
Refers to the association of non polar molecules or components of molecules in the aqueous solution
The hydrophobic effect
Hydrophobic effect is main factors behind
Protein folding
Protein-protein Association
Formation of lipid micelles
Binding of steroid hormones to their receptors
Hydrophobic affect does ___ arise solely because of attractive direct force between two non polar molecules
Not
Water surrounding non polar solutes has _____ entropy
Lower
Non polar portions of the amphipathic molecule aggregate so that ______ water molecules are ordered
Fewer
With high enough concentration of amphipathic molecules, complete aggregation into _____ is possible
Micelles
All hydrophobic groups are sequestered from water; ordered shell of H2O molecules is minimized and entropy is further increased.
Micelles
Hydrophobic effect favors ____ binding
Ligand
Binging sites in enzymes and receptors are often ______
Hydrophobic
(These sites can bind hydrophobic substrates and ligands, such as steroid hormones, which displace water and increase entropy of the system)
Diffusion requires:
- Concentration gradient
2. Method to get across the membrane
Substance passes directly through membrane
Simple diffusion
Substance requires a protein to cross membrane
Facilitated diffusion
Do not depend on the nature of the solute, just the concentration
Ex) bp, mp, and osmolarity
Colligative properties
Depend on the chemical nature of the solute
Ex( viscosity, surface tension, taste, color
Noncolligative properties
Cytoplasm of cells have _____ osmotic pressure dye to dissolved solutes
High
