Acid-Base Relationships Quiz

This chapter focuses on weak interactions in an aqueous environment, crucial for biological systems.
Key concepts include 7 types of noncovalent interactions, differences between hydrophobic, hydrophilic molecules and salts in solution, conjugate acid-base pairs, pH calculations, isoelectric point determination, titration curve analysis, macroion behavior in solution, and small ion effects on macroion interactions.
The overall summary of topics in the chapter are non-covalent interactions, aqueous environments, acid-base equilibria, and how they relate to biological macro-ions.

Proteins are held together by covalent peptide (amide) bonds and their 3-D shape is stabilized by noncovalent bonds.
Nucleic acids are held together by covalent phosphodiester bonds, and their 3-D shape is also stabilized by noncovalent bonds.

Human growth hormone (hGH) binding to its receptor results in increased metabolism and cell growth.
This binding is due to specific noncovalent bonding interactions between hGH and the receptor.

Noncovalent bonds are weak and can be continually broken and reformed, unlike covalent bonds, which are stronger, requiring more energy to break.

Various types of noncovalent interactions exist, including charge-charge, charge-dipole, dipole-dipole, charge-induced dipole, dipole-induced dipole, dispersion (van der Waals) forces, and hydrogen bonds.
Each type has a different dependence on distance, affecting their strength in biological systems.

Noncovalent interactions are electrostatic in nature.
The simplest interactions are between oppositely charged particles (salt bridges).
Coulomb's Law (F = k * q1q2/r^2). governs their strength.
Ionic strength affects the screening effect, impacting interactions in biological systems.

Polar molecules have an asymmetrical internal charge distribution due to differences in electronegativity of atoms: dipole moment
Polar molecules can be attracted to nearby ions (charge-dipole).
Other polar molecules (dipole-dipole interactions).

Dispersion forces (van der Waals) are attractions between molecules with no permanent dipole moment or charge.
Distance critically matters, and the most stable distance is where repulsion and attraction energies are minimized.

Interactions occur between a hydrogen atom covalently bonded to an electronegative atom (O or N) and a pair of nonbonded electrons on a separate electronegative atom.
Hydrogen bonds are among the strongest and most specific noncovalent interactions.
Their strength depends heavily on the electronegative atom involved in bonding.

Water behaves differently than other hydrogen-rich compounds of similar molecular weight due to its high melting point, boiling point and heat of vaporization.
Unique properties including two hydrogen bond donor sites, two hydrogen bond acceptor sites, and its high heat capacity. The high dielectric constant of water plays a crucial role.

Water interacts with positively and negatively charged ions in solution via hydration shells due to water's permanent dipole moment.
High dielectric constant prevents ions from re-forming the ionic compound.

Hydrophilic molecules are water-loving.
Water readily hydrogen bonds with hydrophilic molecules, resulting in dynamic exchanges.
Hydrophilic molecules are often found on protein chain ends.

Hydrophobic molecules are water-hating, avoiding contact with water, and prefer to aggregate.
Formation of clathrate structures, often called water cages, around nonpolar areas is energetically favorable in these conditions. This effect is key in protein and lipid structure.

Amphipathic molecules exhibit both hydrophilic and hydrophobic properties.
They form monolayers, micelles, or bilayers in aqueous solutions to balance these opposing properties.

Acids are proton donors (H+).
Bases are proton acceptors.
Strong acids and bases fully dissociate in water.
Weak acids and bases only partially dissociate.
Ionization of water produces hydronium (H3O+) and hydroxide (OH-) ions
The ion product constant (Kw) relates [H+] and [OH-] concentrations at a given temperature and the relationship applies to water at 25°C. The pH scale is useful to express this.

Weak acids and bases only partially dissociate in water, creating an equilibrium that can be described using the acid dissociation constant (Ka).
pKa helps us measure the relative strength of these acids and bases.

Macroions (large molecules) include polyelectrolytes and polyampholytes, which carry multiple charges.
Like charges repel, while opposite charges attract.
Ionic strength affects how these interactions function in solution.
High ionic strength reduces the forces between macroions because small ions screen them.

Electrophoresis separates charged molecules using an electric field.
Agarose and polyacrylamide gel electrophoresis are common methods to separate molecules based on the size and charge.
Isoelectric focusing utilizes a pH gradient to specifically separate molecules based on their isoelectric point.