ACT Membranes study guide
ACT Membranes · Work through your exam, one topic at a time.
The ACT Membranes credential is presented as a subject examination organized around five equally weighted domains: Membrane Structure and Composition, Membrane Transport, Membrane Signaling and Receptors, Membrane Bioenergetics, and Membrane Dynamics and Trafficking. Each domain carries a 20 percent share of the content outline, so the exam is designed to test breadth across the biology of membranes rather than depth in a single specialty. The ACT Membranes study guide has 5 sections and about 1,480 words.
01Membrane Structure and Composition
Every membrane is a fluid mosaic: a phospholipid bilayer studded with proteins, stiffened by cholesterol in animal cells, and asymmetrically decorated with carbohydrates on the extracellular face. Know the amphipathic logic - hydrophilic heads face water, hydrophobic tails face each other - because nearly every question about membrane behavior traces back to it.
326 words, about 2 min02Membrane Transport
Transport splits into passive (no energy input) and active (energy input). Passive includes simple diffusion through the bilayer (small nonpolar molecules like O2, CO2) and facilitated diffusion through channels or carriers down a gradient.
313 words, about 2 min03Membrane Signaling and Receptors
Cells receive signals through membrane receptors that convert an extracellular ligand into an intracellular response - signal transduction. Know the major receptor classes: G protein-coupled receptors (GPCRs, seven transmembrane helices, activate heterotrimeric G proteins), receptor tyrosine kinases (RTKs, dimerize and autophosphorylate), ion-channel-linked receptors, and ligand-gated nuclear receptors (though these are intracellular).
273 words, about 1 min04Membrane Bioenergetics
Membrane bioenergetics centers on the chemiosmotic theory: electron transport chains pump protons across a membrane, creating an electrochemical proton gradient (proton-motive force) that drives ATP synthesis through ATP synthase. In mitochondria, the inner membrane hosts the electron transport chain and ATP synthase; the gradient is high outside (intermembrane space) and low inside (matrix).
306 words, about 2 min05Membrane Dynamics and Trafficking
Membranes are dynamic: they bud, fuse, and exchange material through vesicles. Know the secretory pathway (ER → Golgi → plasma membrane or lysosome) and endocytic pathways (phagocytosis, pinocytosis, receptor-mediated endocytosis).
262 words, about 1 min