Question

1. Define the steps of gene expression. Be sure to specifically speak to the following: (USL05.1) DNA Replication Transcription Translation

Answer 1

The steps of gene expression are DNA replication, transcription and translation. They are explained as follows :-

DNA replication -

• In this process, the two strands of DNA separate out and each serve as a template for the synthesis of the daughter strand, thus copying the information in a semi-conservative manner.
• Replication is primarily carried out by the formation of a replication fork.
• The main enzymes involved are topoisomerase, helicase, DNA polymerse and ligase.
• Replication is an essential step as it is needed to ensure that the daughter cells formed after cell division receive the exact same genetic information as that of the parent cell.

Transcription -

• In this process, the information in the DNA is copied into the messenger RNA (mRNA).
• The main enzyme involved in this process is RNA polymerase. The mRNA formed serves as the blueprint for the synthesis of proteins.
• The nascent mRNA before undergoing translation, goes in for necessary modifications like capping, poly-A-tailing and splicing. Capping helps in translation initiation, splicing helps in removing introns and retains exons (introns are non coding junk sequences) and poly-A-tailing protects the nascent mRNA.

Translation -

• This is the process of protein synthesis where the mRNA binds to the ribosome and recruits specific tRNAs that carry the specific amino acids as per the mRNA code.
• These amino acids then form the peptide bond resulting in the formation of polypeptide chains. This is catalysed by the enzyme peptidyl transferase.
• These polypeptide chains undergo further modification to form the necessary proteins.
• Post translation, the mRNA is degraded as its purpose is served.