Question

Membrane-bound receptors are an important component facilitating some types of cellular communication; however, not all signal-receptor binding occurs outside the cell membrane. Some signal molecules are able to pass through the plasma membrane, and their receptors are intracellular. In a theoretical lab study, scientists work to design a lab experiment that would inhibit some molecules’ ability to bind with their intracellular receptors. (a) Draw conclusions about the structure and function of membrane proteins. (b) Identify some molecules that are able to pass through the plasma membrane to bind with their intracellular receptors. (c) Explain what needs to be the focus of the scientists’ study in order to inhibit signal molecules from reaching and binding to their intracellular receptors and thereby enabling the signal transduction pathway. Justify your answer. (d) Discuss how the inhibition of these molecules will affect protein production.

Answer 1

A. structure and function of membrane proteins :

• Receptor-mediated endocytosis : The particular molecule which will bind to the intracellular receptor, first bound to its plasma carrier protein, then brought into the cell via a cell-surface receptor. The complex is broken down by the lysosome, and after that free molecule diffuses into the cell, where it subsequently exerts its action at the genomic level or undergoes metabolism after binding with the intracellular receptor.
• Signalling through cell-surface receptors. The free molecule alters intracellular signalling by binding to cell-surface receptors. These receptors are either GPCR or other membrane spanning protein. After binding with that particular molecule, structural change has occurred in these receptor and these leads to a signal to other intracellular molecule and then exerts its action at the genomic level.

B. Receptors for steroid, thyroid hormones and the IP₃ receptor located on the endoplasmic reticulum are located inside target cells, in the cytoplasm or nucleus, and function as ligand-dependent transcription factors. The hormone-receptor complex binds to promoter regions of responsive genes and stimulates or sometimes inhibits transcription from those genes.

C. The main focus of the scientists’ study in order to inhibit signal molecules from reaching and binding to their intracellular receptors and thereby enabling the signal transduction pathway is to know about the function of that particular molecule. Because if we inhibit a particular path of function of molecule we can easily identify what it actually works. In this way scientist can easily identify the proper function of different molecules.

D. Normally after getting inside the cell, many of these molecules bind to proteins that act as regulators of mRNA synthesis to mediate gene expression. Gene expression is the cellular process of transforming the information in a cell's DNA into a sequence of amino acids that ultimately forms a protein. When the ligand binds to the internal receptor, a conformational change exposes a DNA-binding site on the protein. The ligand-receptor complex moves into the nucleus, binds to specific regulatory regions of the chromosomal DNA, and promotes the initiation of transcription . Internal receptors can directly influence gene expression without having to pass the signal on to other receptors or messengers.

If these molecules are inhibited they do not alter the gene expression as well as desired protein production. As a result proper working machinery will hampered and it will exert an abnormal function.