Curriculum
Module 02 · 70 min
Membrane Biophysics & Transport
Lipid bilayers, channels, pumps and the currencies of compartmentalisation.
CoreClinicalResearch
Topics
What this module covers
- 01Lipid composition, asymmetry, and phase behaviour (rafts, ordered domains)
- 02Passive vs facilitated diffusion; Fick's law in cell-biology terms
- 03Primary, secondary, and tertiary active transport (Na/K-ATPase, SGLT, NHE)
- 04Ion channels: voltage-, ligand-, and mechano-gated
- 05Membrane potential, Nernst, Goldman-Hodgkin-Katz
- 06Aquaporins, lipid scramblases, flippases
Deep dives
Lesson sub-pages
Learning objectives
By the end of this module you will be able to
- L01Calculate equilibrium potentials and predict the direction of ion flux from concentration and voltage gradients.
- L02Match a channel/transporter family to its inhibitor and a clinical use of that inhibitor.
- L03Explain why phosphatidylserine externalisation is a biological signal, not a leak.
Expected takeaways
What you should walk away believing
- →The membrane potential is set primarily by K+ at rest and Na+ during action potentials.
- →Most clinically important diuretics, antiarrhythmics, anticonvulsants, and antidepressants act on transporters or channels.
- →Lipid asymmetry is actively maintained at ATP cost — its loss is itself a death signal.
Core summary
At the Core level
Membranes don't just enclose cells — they store energy as electrochemical gradients, segregate biochemistry into compartments, and host the receptors that connect a cell to the outside world. Channels move ions down gradients in milliseconds. Pumps build the gradients in seconds. Lipid composition tunes both, and lipid asymmetry between leaflets is a maintained signal.
Myth vs reality
Common misconception
Claim
Lipid bilayers are passive barriers.
Reality
Bilayers signal: PI(4,5)P2 recruits dynamin and ion channel modulators; PS externalisation tags apoptotic cells; cholesterol-rich domains organise signalling complexes. Loss of asymmetry is itself information.
Evidence-graded claims
Claims, scored A–F
A
The Nernst equation predicts ion equilibrium potentials accurately at 37°C
Foundational physical chemistry, used clinically in EP.
C
Lipid rafts are stable, microscopically visible domains
Existence of nanoscale ordered domains is supported; large stable rafts are contested.
C
Ivacaftor restores function to most CFTR mutations
Effective for gating mutants (G551D); class-specific. Combination needed for F508del.
Quiz
Check your understanding
Q1. At 37°C with [K+]o = 4 mM and [K+]i = 140 mM, the K+ equilibrium potential is approximately:
Q2. Which transporter is the target of loop diuretics?
Q3. Phosphatidylserine externalisation signals…
Flashcards
Lock it in
1 / 4
Front
Goldman-Hodgkin-Katz equation purpose?
Click to flip
Suggested reading
Primary literature
- The fluid mosaic model after 50 years — Nicolson, BBA-Biomembranes 2014 ↗
- Cryo-EM structures of Nav channels — Pan et al., Science 2018 ↗