<P> One study has found that these steroid - carrier complexes are bound by megalin, a membrane receptor, and are then taken into cells via endocytosis . One possible pathway is that once inside the cell these complexes are taken to the lysosome, where the carrier protein is degraded and the steroid hormone is released into the cytoplasm of the target cell . The hormone then follows a genomic pathway of action . This process is shown in Figure 2 to the right . The role of endocytosis in steroid hormone transport is not well understood and is under further investigation . </P> <P> In order for steroid hormones to cross the lipid bilayer of cells they must overcome energetic barriers that would prevent their entering or exiting the membrane . Gibbs free energy is an important concept here . These hormones, which are all derived from cholesterol, have hydrophilic functional groups at either end and hydrophobic carbon backbones . When steroid hormones are entering membranes free energy barriers exist when the functional groups are entering the hydrophobic interior of membrane, but it is energetically favorable for the hydrophobic core of these hormones to enter lipid bilayers . These energy barriers and wells are reversed for hormones exiting membranes . Steroid hormones easily enter and exit the membrane at physiologic conditions . They have been shown experimentally to cross membranes near a rate of 20 μm / s, depending on the hormone . </P> <P> Though it is energetically more favorable for hormones to be in the membrane than in the ECF or ICF, they do in fact leave the membrane once they have entered it . This is an important consideration because cholesterol--the precursor to all steroid hormones--does not leave the membrane once it has embedded itself inside . The difference between cholesterol and these hormones is that cholesterol is in a much larger negative Gibb's free energy well once inside the membrane, as compared to these hormones . This is because the carbohydrate tail on cholesterol has a very favorable interaction with the interior of lipid bilayers . </P> <P> There are many different mechanisms through which steroid hormones affect their target cells . All of these different pathways can be classified as having either a genomic effect, or a non-genomic effect . Genomic pathways are slow and result in altering transcription levels of certain proteins in the cell; non-genomic pathways are much faster . </P>

Which of the following is a function of a steriod