Biophysical Chemistry

Biophysical Chemistry

Biophysical chemistry applies principles of physics and chemistry to understand biological systems — particularly how molecules interact, how energy flows through biochemical reactions, and how thermodynamics governs life processes.

pH and Ionization

The Henderson-Hasselbalch equation: pH = pKa + log([A⁻]/[HA]). At pH = pKa, 50% of the acid is ionized. Amino acids exist as zwitterions at their isoelectric point (pI). At pI, net charge = 0; migration in electric field = 0 (important for electrophoresis and isoelectric focusing).

Buffer Systems

Buffers resist pH change upon addition of acid or base. Effective within ±1 pH unit of pKa.

  • Bicarbonate buffer (blood): CO₂/HCO₃⁻, pKa = 6.1. Most important extracellular buffer. Regulated by lungs (CO₂) and kidneys (HCO₃⁻).
  • Phosphate buffer (intracellular): H₂PO₄⁻/HPO₄²⁻, pKa = 6.8. Important in urine and intracellular fluid.
  • Protein buffer: Side chains of His (imidazole, pKa ~6) act as buffers in blood (Hb is major blood buffer).

Thermodynamics in Biochemistry

  • Gibbs Free Energy (ΔG): ΔG = ΔH - TΔS. If ΔG < 0, reaction is spontaneous (exergonic). If ΔG > 0, reaction requires energy input (endergonic).
  • Standard Free Energy (ΔG°'): At pH 7, 25°C, 1 M concentrations. Used to compare reactions thermodynamically.
  • ATP hydrolysis: ΔG°' = -30.5 kJ/mol. ATP acts as the universal energy currency coupling exergonic & endergonic reactions.
  • Coupled reactions: Unfavorable reactions driven by coupling with ATP hydrolysis (or other favorable reactions).

Molecular Forces in Biomolecules

  • Covalent bonds: Strongest (peptide, glycosidic, phosphodiester bonds). Form the backbone of biomolecules.
  • Hydrogen bonds: Responsible for DNA base pairing, protein secondary structure, water's properties.
  • Hydrophobic interactions: Nonpolar groups cluster away from water → drives protein folding and membrane formation.
  • Van der Waals forces: Weak, transient dipole interactions. Important in enzyme-substrate fitting.
  • Ionic interactions (salt bridges): Electrostatic attractions between charged groups — important in protein structure.

Colligative Properties & Osmosis

Osmolality of body fluids is ~290 mOsm/kg H₂O. Osmotic pressure drives water across membranes. Oncotic pressure (due to plasma proteins, mainly albumin) keeps fluid in blood vessels. Low albumin → edema.

Spectroscopy

  • UV absorption: Proteins absorb at 280 nm (Trp, Tyr); nucleic acids at 260 nm.
  • Beer-Lambert Law: Absorbance = ε × c × l. Used in all colorimetric lab assays.
  • CD (Circular Dichroism): Detects protein secondary structure (α-helix vs β-sheet).

Quiz - Exam Preparation Strategy

When studying Quiz for your final board exams, it is critical to focus on the core concepts and fundamental formulas. Relying strictly on NCERT textbook solutions and practicing previous year questions (PYQs) is the proven methodology for scoring high marks. Avoid rote memorization and instead focus on the logical application of the theories presented in this chapter.

⚠️ Common Mistakes to Avoid

❓ Frequently Asked Questions

How can I quickly memorize the concepts of Quiz?

The most effective way is to create short, handwritten revision notes and continuously test your knowledge using our interactive Mock Tests. Spaced repetition and active recall are much better than passive reading.

What type of questions are most commonly asked from Quiz?

Board exams tend to favor conceptual application questions and direct formula-based derivations from the NCERT syllabus. Ensure you have solved every single exercise in the official textbook.

Is reading the NCERT book enough for this chapter?

Yes, the NCERT textbook is the absolute gold standard for board exams. However, to improve your speed and accuracy during the actual exam, you must supplement your reading by solving timed mock tests and objective questions.