Biochemistry: Lecture 2

What are aqueous environments?

They are environments in which water is the solvent.

Why are aqueous environments important to proteins?

Aqueous environments allow for proteins to naturally exist, fold, and function, which dictate their formation, structure, stability, and function.

What qualities of aqueous environments benefit proteins?

Aqueous environments provide a versatile medium for biochemical interactions, dissolve polar and charged biomolecules, and stabilize folded protein structures.

How does water impact protein folding?

Water influences protein folding through the hydrophobic effect, where nonpolar amino acids cluster to minimize unfavorable ordering of water molecules.

How do water's properties influence biochemical reactions?

Water's properties, such as its dipole and hydrogen-bonding network, make it the primary medium for biochemical reactions and often a reactant.

How are biochemical reactions related to protein folding?

Both rely on non-covalent forces governed by the thermodynamic and chemical properties of the aqueous environment.

What is an enzymatic mechanism?

An enzymatic mechanism is the sequence of chemical events by which an enzyme converts substrates into products.

Why is the cytoplasm an aqueous solution?

The cytoplasm is predominantly composed of water containing dissolved ions, small molecules, and macromolecules.

What is solvation and how does it relate to the cytoplasm?

Solvation is the interaction of solvent molecules around solute particles; in the cytoplasm, water solvates polar and ionic solutes.

What are the properties of water?

Water is a polar molecule with a permanent dipole, strong hydrogen-bonding capability, and acts as a versatile solvent.

Why does water contain a permanent dipole?

Water's permanent dipole arises from the unequal sharing of electrons between oxygen and hydrogen, creating an asymmetric charge distribution.

How does electronegativity difference lead to a strong dipole in water?

Oxygen's high electronegativity compared to hydrogen creates a significant difference, pulling electron density and establishing distinct poles.

How do water's properties lead to hydrogen bonding?

Water's polar covalent bonds and permanent dipole enable electrostatic attraction to lone pairs on neighboring electronegative atoms.

What are some qualities of hydrogen bonds?

Length: ~1.8 Å; Strength: ~20 kJ/mol; Stability: most stable when donor, hydrogen, and acceptor are aligned linearly.

What is a hydrogen bond donor?

A hydrogen bond donor is a hydrogen atom(H+) covalently attached to a strongly electronegative atom, giving it a large partial positive charge.

What are some examples of hydrogen bond donors?

Examples include the O-H group in water and acetic acid, and N-H groups in ammonia or amines.

What is a hydrogen bond acceptor?

A hydrogen bond acceptor is an electronegative atom(N,O,F) with a large partial negative charge and at least one unshared lone pair.

What are some examples of hydrogen bond acceptors?

Examples include oxygen in water(H₂O) molecules, carbonyl oxygens(C=O), and hydroxyl(-OH) oxygens.

How does hydrogen bonding work in steps?

1. Electron distribution creates partial charges. 2. Partially positive hydrogen approaches lone pair of an electronegative atom. 3. Electrostatic attraction forms.

What are some examples of hydrogen bonds?

Intermolecular hydrogen bonds in water, hydrogen bonding in acetic acid dimers, and salt bridges between amino acids.

How does hydrogen bonding differ in water and ice?

In ice, water forms a rigid lattice with 4 hydrogen bonds; in liquid water, the bonding network is dynamic and flexible.

What are the trade-offs between bonding in water and ice?

Ice maximizes hydrogen bonding at the expense of mobility, while liquid water sacrifices bonding perfection for fluidity.

How does this relate to Free Gibbs Energy?

Protein folding and molecular interactions are thermodynamic processes driven by changes in enthalpy and entropy, determining Gibbs Free Energy.

What is Free Gibbs Energy?

Free Gibbs Energy is a thermodynamic quantity that combines enthalpy and entropy to predict the spontaneity of a process.

What is Gibbs Free Energy (G)?

G is the thermodynamic potential measuring the maximum reversible work of a system at constant temperature and pressure.

What indicates a spontaneous biochemical process?

A negative Gibbs Free Energy (G<0) indicates spontaneity.

What are dipole-dipole interactions?

Electrostatic forces between molecules with permanent dipoles.

What criteria are necessary for dipole-dipole interactions?

Molecules must contain polar covalent bonds with a significant electronegativity difference.

How do dipole-dipole interactions work in steps?

Step 1: Unequal sharing of electrons creates partial positive and negative poles. Step 2: Electrostatic attraction occurs between opposite poles.

What are examples of dipole-dipole interactions?

Interactions between acetone molecules or iodine chloride (I-Cl) molecules.

What are ionic bonds?

Strong electrostatic attractions between oppositely charged ions formed by complete electron transfer.

How do ionic bonds work?

An electron is transferred from a metal atom to a nonmetal atom, forming cations and anions that bind in a crystal lattice.

Are ionic interactions relevant in biochemistry?

Yes, they stabilize protein structures and facilitate salt bridges.

What are salt bridges?

Stabilizing interactions in proteins formed by electrostatic attraction and hydrogen bonding between charged amino acid side chains.

How do salt bridges work in steps?

Step 1: Ionization of acidic and basic side chains. Step 2: Electrostatic attraction and hydrogen bonding between opposing charges.

How do biological salt bridges differ from standard ionic bonds?

They occur locally between specific charged side chains and involve concurrent hydrogen bonding.

Why are both electrostatic and hydrogen bonding present in salt bridges?

Because interacting functional groups have both formal/partial charges and hydrogen bond donors/acceptors.

Which molecules typically form salt bridges?

Charged amino acid side chains, specifically acidic (like glutamic acid) and basic residues (like lysine).

How do nonpolar molecules relate to biochemistry?

They are essential for forming biological membranes, storing energy, and driving protein folding.

What are London Dispersion Forces (LDFs)?

The primary intermolecular forces that attract nonpolar molecules through transient electrostatic interactions.

How do LDFs work between nonpolar molecules in steps?

Step 1: Electrons move within orbitals. Step 2: Temporary shifts create instantaneous dipoles. Step 3: Induced dipoles in adjacent molecules create attraction.

What is the randomness aspect of LDFs?

It stems from the continuous movement of electrons, causing temporary dipoles to fluctuate.

What is a micelle?

A spherical cluster formed by amphipathic molecules in water, with hydrophilic heads outward and hydrophobic tails inward.

How are micelles stabilized?

By London Dispersion Forces acting between tightly packed nonpolar hydrocarbon tails.

What drives the formation of LDFs in micelles?

The hydrophobic effect, where nonpolar tails cluster to maximize favorable LDF interactions.

What is dissolution?

The process by which a solute incorporates into a solvent to form a solution.

How does dissolution work for polar solutes in water?

Step 1: Water orients around polar particles. Step 2: Water disrupts internal electrostatic interactions. Step 3: Hydration shells form, increasing entropy.

How does water interact with nonpolar solutes?

Water cannot form hydrogen bonds, leading to structured cage-like formations around nonpolar solutes.

How does this interaction affect enthalpy and entropy?

Enthalpy increases due to disruption of hydrogen bonding; entropy decreases due to ordered water patterns.

What is the hydrophobic effect?

The tendency of nonpolar substances to aggregate in water to minimize unfavorable interactions.

How does the hydrophobic effect relate to water's interactions with nonpolar solutes?

Nonpolar solutes disrupt hydrogen bonding, forcing water into clathrate cages, decreasing entropy and increasing enthalpy.

How is the lipid bilayer an example of the hydrophobic effect?

Phospholipids' nonpolar tails cluster away from water, forming a bilayer with hydrophilic heads interfacing with water.

What is a clathrate cage?

A shell of highly ordered water molecules surrounding a nonpolar moiety.

How does solute concentration affect solvation?

Higher solute concentrations increase the solution's osmotic pressure.

How does solute concentration affect water movement?

Water migrates via osmosis from lower to higher solute concentrations.

What is osmotic pressure?

The pressure required to resist osmosis.

What is the equation for osmotic pressure?

π = icRT.

What do the variables in the osmotic pressure equation represent?

π is osmotic pressure, i is the van't Hoff factor, c is molar concentration, R is the ideal gas constant, T is absolute temperature.

What are isotonic, hypertonic, and hypotonic solutions?

Isotonic: equal osmolarity; Hypertonic: higher osmolarity; Hypotonic: lower osmolarity.

How does each solution affect water movement?

Isotonic: no net movement; Hypertonic: water moves out; Hypotonic: water moves in.

How does each solution affect a cell's structure?

Isotonic: normal structure; Hypertonic: cell shrinks; Hypotonic: cell swells or bursts.