function perturb function A perturb function is a function that disrupts the normal function of a system induced through either internal or external means. External means of perturbation include: (1) displacement fields in the physical sense - e.g., temperature change, osmotic shock, pressure change; (2) application of small molecules such as drugs or toxins to perturb the function of specific pathways or application of surfactants to perturb the normal function of plasma membrane. Internal means of perturbation include: (1) manipulation of gene function via gene knockout or transcript knockdown via RNAi; (2) directed genetic mutation leading to minimal aa alterations that interfere with peptide function.