Question

Compare and contrast activation of a cell by peptide versus steroid hormones. Include at least one similarity and one difference in your answer. Remember that all answers must be specific, complete, and in full sentences to count for full credit

Answer 1

Steroid hormones are fat soluble so they pass through the plasma membrane and enter the nucleus. There they bind to DNA and start the synthesis of the hormone. The synthesis of steroid hormones occurs in the smooth endoplasmic reticulum when needed. Since steroid hormones are small hydrophobic molecules, they can freely diffuse through the lipid bilayer of the plasma membrane. They bind to a specific receptor inside the cytoplasm, and this receptor-bound steroid hormone complex is transported into the nucleus. This receptor-bound steroid hormone complex then binds to specific regions on chromatin. This binding either activates or releases the associated proteins of chromatin to modify the transcription. In the end, the steroid hormone determines the amount of a particular protein in the cell. Thereby, the receptor-bound steroid hormone complex acts as a transcription regulator.

Peptide hormones refer to any hormone derived from amino acids. They can be either small or large hydrophilic molecules synthesized in the rough endoplasmic reticulum. Peptide hormones are stored in vesicles until the signals are received for the secretion. Since they are hydrophilic molecules, peptide hormones are unable to freely diffuse through the lipid bilayer. Therefore, the receptors for the peptide hormones are located on the surface of the target cell. These receptors are made up of a single polypeptide chain, which comprises domains on either side of the plasma membrane. These intracellular and extracellular domains are connected by a membrane-spanning domain.

Some of the receptors are composed of multiple polypeptides. The peptide hormones are the first messengers of the signaling pathway. The binding of the peptide hormone to the receptor activates the G-protein, which is located in the membrane. The activated G-protein stimulates enzymes such as adenyl cyclase and phospholipase C in the plasma membrane, producing second messengers such as cyclic AMP (cAMP). Those second messengers bind to the protein kinase A. The activated protein kinase A phosphorylates other proteins, initiating a signal cascade to modify various functions of the cell.

Similarities Between Steroid and Peptide Hormones

They both require a receptor or a protein to bind. Steroid hormone requires a receptor outside the cell where a peptide hormone requires a receptor inside the cell.

•             Both steroid and peptide hormones are signaling molecules that regulate the physiology and the behavior of organs.

•             Both steroid and peptide hormones are produced in the endocrine glands and released into the bloodstream in order to be transported to the target organ.

•             Typically, both steroid and peptide hormones exert a prolonged action.