4. Equilibrium

Explain chemical equilibrium, thermodynamic concepts, and enzyme roles in cells

Chemical equilibrium occurs when forward and reverse reaction rates are equal and reactant/product concentrations remain constant. Thermodynamics dictates reaction spontaneity (DeltaG < 0). Enzymes act as biological catalysts that lower activation energy to speed up reactions without altering equilibrium positions or DeltaG.

Describe eukaryotic and prokaryotic cell morphology and membrane transport mechanisms

Eukaryotes have membrane-bound organelles and a nucleus; prokaryotes lack a nucleus/organelles. Membrane transport includes passive mechanisms (simple/facilitated diffusion down concentration gradients) and active mechanisms (primary/secondary transport against gradients using ATP or ion gradients).

Account for basic methodology in purifying, analyzing, and visualizing DNA and proteins

Purification: Cell lysis, centrifugation, precipitation, and chromatography (affinity, ion-exchange, size-exclusion). Analysis/Visualization: Gel electrophoresis (agarose for DNA, SDS-PAGE for proteins), spectrophotometry (A260 for DNA, A280/Brdford for protein), and staining/fluorescence (ethidium bromide/fluorescent dyes).

Define and use thermodynamic equilibrium constant K

K is the ratio of product concentrations to reactant concentrations at equilibrium, each raised to the power of their stoichiometric coefficients (K = [C]^c[D]^d / [A]^a[B]^b). K > 1 favors products; K < 1 favors reactants.

Define and use reaction quotient Q

Q uses the same mathematical expression as K (Q = [C]^c[D]^d / [A]^a[B]^b), but measures concentrations at any given non-equilibrium point. If Q < K, reaction shifts right; if Q > K, reaction shifts left; if Q = K, system is at equilibrium.

Define and explain relation between DeltaG and K

DeltaG° = -RT ln(K). DeltaG° indicates standard free energy change. If K > 1, DeltaG° is negative (spontaneous under standard conditions); if K < 1, DeltaG° is positive (non-spontaneous under standard conditions).

Describe how K and composition change with pressure, concentration, and temperature

Changing concentration or pressure alters system composition (Q) to restore equilibrium, but does NOT change K. ONLY changing temperature changes the actual numerical value of K (endothermic reactions increase K with higher T; exothermic reactions decrease K with higher T).

Explain Le Chatelier's principle in biological systems

If a dynamic equilibrium is disturbed by changing conditions (temperature, pressure, concentration), the system shifts to counteract the change. In cells, continuous removal of products by subsequent metabolic reactions constantly pulls equilibria forward.

Describe how chemical/physical properties affect partition equilibrium between phases

Partitioning depends on molecular polarity, hydrophobicity, charge state, and hydrogen-bonding capacity. Hydrophobic/non-polar molecules partition preferentially into organic/lipid phases, while charged/polar molecules remain in aqueous phases.

Explain diffusion

The passive net movement of solute molecules down a concentration gradient from an area of higher concentration to an area of lower concentration driven by random thermal motion until uniform.

Explain osmosis

The passive movement of solvent (water) molecules across a selectively permeable membrane from a region of lower solute concentration (higher water concentration) to a region of higher solute concentration.

Explain active and passive transport

Passive transport moves substances down their concentration gradient without energy input (e.g., simple diffusion, channels, carriers). Active transport moves substances against their concentration gradient using energy (ATP hydrolysis or coupled ion gradients).

Explain protein-ligand interaction

Reversible, non-covalent binding between a protein (binding site) and a specific molecule (ligand). Driven by hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals forces; quantified by dissociation constant Kd.

Explain chromatography techniques on a basic level

Separation of mixtures based on differential partitioning between a stationary phase and a mobile phase. Includes size-exclusion (separates by size), ion-exchange (separates by net charge), and affinity/reverse-phase (separates by specific binding or hydrophobicity).