Quiz 16: Protein Synthesis and Degradation


The tetracycline is an antibiotic which is used for the treatment of bacterial infections. This antibiotic attaches to the A site of the bacterial protein synthesis. The protein synthesis process includes two major steps that are transcription and translation. The transcription process is the one in which the mRNA (messenger Ribonucleic acid) is synthesized complementary to the coding strand of the DNA molecule. The translation is the process in which the amino acids are attached according to the codons (set of three base pairs) of the mRNA for the synthesis of proteins. The translation process occurs in the ribosome which has an A (acceptor), P (promoter) and E (exit) sites. Thus, the A site is involved in translation hence if the antibiotic will bind to the A site then it will inhibit the translation process of protein synthesis.

In G-protein coupled signaling, G-protein, and adenylyl cyclase are the two major proteins involved, and secondary messenger is cAMP. Ligand binds to the G-protein coupled receptor. This binding brings conformational change that leads to G-protein activation. The alpha unit of the G-protein is bound with GDP (guanine diphosphate), but when activated it is replaced with GTP (Guanine triphosphate). Then the activated G-protein binds with adenylate cyclase to activate it. Activated adenylate cyclase produces cAMP (cyclic adenosine monophosphate). The cAMP molecules bind to the regulatory subunits present in the protein kinase A that releases active catalytic subunits. The catalytic subunits reach the nucleus to activate target genes. The action of G-proteins involved in hormonal regulation is similar to those involved in the synthesis of proteins. This is because in protein synthesis also the amino acids are attached to the acceptor and then to promoter and released on the completion of the protein synthesis. Similarly, the G-proteins in the hormonal regulation bind to the GDP and detaches only on the formation of GTP that is on the completion of the process.

The regulation of translation in prokaryotes cannot be explained with any example because in prokaryotes both transcription and translation are coupled, so the translation begins while the mRNA (messenger ribonucleic acid) is still being synthesized. However, transcriptional gene regulation is observed in prokaryotes; for example, lac operon. The lac operon contains two types of genes-structural genes and regulatory genes. The genes that can be transcribed into mRNA (messenger ribonucleic acid) come under structural genes. There are three structural genes present in the lac operon, they are lac z, lac y, and lac a. There are two regulatory genes present in lac operon-the operator and the promoter, which cannot be transcribed.