View Full Version : Endocrine Glands

04-25-2005, 01:27 AM
Explain why direct gene activation is a possible mechanism of action for steroid hormones, but not for peptide hormones.

05-07-2005, 03:28 PM
I think that it is because peptide hormons are hydrosoluble so they can't enter the cell and come into the nucleus to stimulate some genes, but they can only act by binding to their membrane receptors and trigger a transduction of signal (second messenger: cAMP, IP3, cGMP) . But eventually, they even can sometimes activate some transcription factors and activate some genes (protein kinase A can do it).
Steroid hormones are lyposoluble so they can easily go through the cell membrane by simple diffusion and then come into the nucleus to activate gene transcription.

10-11-2005, 10:59 AM
Steroids act directly upon nuclei to make proteins in the target cells that will carry out specific functions. Peptides are proteins already, so they utilize second messengers to help carry out their effects upon target cells.

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