Biochem Bonding, forces, ionization 8/6

What molecular substitution leads to sickle cell anemia?

Replacement of a polar molecule (C3O2H5) with a hydrophobic, non-polar molecule (C3H7).

Why does the substitution in sickle cell anemia cause disease?

The hydrophobic substitution disrupts normal polar interactions in hemoglobin, altering its behavior and causing cell sickling.

What is the state of a carboxylic acid at physiological pH?

It exists in the conjugate base state, with a full ionized oxygen due to loss of H⁺.

How does polarity affect molecular location in the body?

Hydrophilic (polar) molecules are found in aqueous environments; hydrophobic (non-polar) molecules cluster away from water.

What are covalent bonds and their strength?

Bonds formed by sharing electrons; very strong and stable.

What are ionic bonds and how do they behave in water?

Electrostatic interactions between oppositely charged ions; weak in water due to hydration, up to 100x weaker than in a vacuum.

What are van der Waals forces?

Weak electrostatic interactions between neutral molecules due to temporary partial charges.

What causes van der Waals interactions?

Differences in electronegativity causing uneven electron distribution and induced dipoles.

What are hydrogen bonds and what causes them?

Bonds due to unequal electron distribution, like between hydrogen and more electronegative atoms (e.g., oxygen).

What are London dispersion forces?

Weak interactions from temporary dipoles caused by proximity of electron clouds; individually weak but collectively strong.

What are hydrophobic interactions?

Nonpolar molecules avoid water and cluster together, increasing entropy of the system.

How do water molecules interact with ions?

Water forms hydration shells that insulate and stabilize charged ions through electrostatic attraction.

Why is water a good solvent for polar molecules?

Water interacts via dipole moments and van der Waals forces, stabilizing charged or polar solutes.

How do non-polar solutes behave in water?

They aggregate to reduce contact with water, causing water molecules to become more disordered (increase in entropy).

What is Brownian motion in the oil-water context?

Oil molecules move randomly; water and oil are disordered except at the interface.

How do enthalpy and entropy influence solubility?

Favorable enthalpy (attractive interactions) and increased entropy (disorder) drive solubility, especially for ions in water.

How does pH affect the ionization state of a molecule?

It shifts the equilibrium between conjugate acid and base, changing the net charge of the molecule.

What equation describes the relationship between pH and ionization?

The Henderson-Hasselbalch equation.

What happens to a weak acid at a pH above its pKa?

It exists mostly in the deprotonated (conjugate base) form.

What is a buffer?

A solution that resists changes in pH upon the addition of strong acid or base.

What makes a good buffer?

A weak acid and its conjugate base, most effective within ±1 pH unit of its pKa.

How does a buffer resist pH changes?

Added protons react with the base, and added hydroxide ions react with the acid, keeping pH stable.

How do you select a polyprotic acid for buffering at a specific pH?

Choose the ionization step with a pKa closest to the target pH.

What is the physiologically relevant pH for buffer selection?

Around pH 7.4, which matches many biological processes.

What factors influence the melting point of fatty acids?

Chain length (longer = higher melting point) and number of double bonds (more = lower melting point).

What is a saturated fatty acid?

A fatty acid with no double bonds; straight chain and higher melting point.

What is a cis unsaturated fatty acid?

Has double bonds with hydrogens on the same side; creates kinks and lowers melting point.

What is a trans unsaturated fatty acid?

Hydrogens on opposite sides of the double bond; behaves more like saturated fat and increases cholesterol.

What does amphipathic mean?

A molecule that has both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.

Give an example of an amphipathic molecule.

Phospholipids; they form bilayers due to their dual nature.

How does saturation affect triacylglycerol properties?

More saturated fats are solid at room temp; more unsaturated fats are liquid.

Why does more saturation increase solidity?

Saturated chains pack tightly together, increasing melting point.

What is the impact of more double bonds in triacylglycerol?

Loosens packing, lowers melting point, and increases fluidity.

What is the fluid mosaic model?

Describes the membrane as a flexible, dynamic structure composed of lipids and proteins.

How does membrane composition affect fluidity?

Saturated fats decrease fluidity; unsaturated fats and cholesterol increase it.

How does membrane composition affect protein function?

Fluidity changes influence protein movement, signaling, and function in the membrane.