Gene expression is the intricate process involving a gene, serving as the starting point for genetic activity. This process entails the utilization of gene information to produce gene products, typically proteins or RNA molecules, through a cascade of several stages. The two principal stages in gene expression are transcription and translation.
Transcription
Transcription, the initial step, takes place in the nucleus in eukaryotes and in the cytoplasm in prokaryotes. During transcription, the DNA is transcribed into messenger RNA (mRNA) by the enzyme RNA polymerase. The mRNA, acting as a carrier of genetic information, travels to the cytoplasm through nuclear pores. Upon reaching the cytoplasm, it associates with ribosomes, initiating the translation process. This subsequent stage involves the synthesis of proteins or RNA molecules based on the information encoded in the mRNA. The collaboration between transcription and translation orchestrates the comprehensive gene expression process.
Translation:
In the translation process, mRNA, ribosomes, tRNA, and enzymes work in concert. This intricate mechanism involves the information carried by mRNA, which binds to specific sites on ribosomes. As the mRNA codons are read by the ribosomes, tRNA molecules bring in specific amino acids, forming a complex with the ribosome. Subsequently, these amino acids join together, facilitating the synthesis of a polypeptide chain. The resulting chain undergoes folding, ultimately yielding a functional protein. This highly coordinated interplay of molecular components characterizes the final stages of gene expression, culminating in the production of biologically active proteins.
Gene expression is highly regulated and responsive to internal and external signals. Cells can adjust the level of protein production based on the needs of the organism and its environment.
The Central Dogma of molecular biology:
The flow of genetic information in a biological system is called the Central Dogma of life, developed by Y. Francis Crick. This process is where information is stored, copied, and expressed in organisms.
- Replication: The process by which DNA makes an identical copy of itself. This occurs before cell division, ensuring that each daughter cell receives complete genetic information.
- Transcription: Synthesis of mRNA from a DNA template. During transcription, the genetic information contained in the DNA sequence is transcribed into an mRNA molecule.
- Translation: The process by which the information carried by mRNA is used to make the corresponding protein. It occurs in the ribosomes in the cytoplasm, where tRNA molecules carry the required amino acids.
The Central Dogma is often summarized as “DNA makes RNA protein.” While the flow of information is generally unidirectional, there are some exceptions, such as reverse transcription in retroviruses, where RNA is used to synthesize DNA. Despite these exceptions, the central dogma provides a fundamental understanding of the basic processes that govern the flow of genetic information in cells.
