Nucleic Acids And Protein Synthesis - Session 3

We know that information in DNA is used to build proteins. But how is this information in DNA is used to build proteins? This happens through gene expression. Gene expression refers to the process by which the genetic information encoded within a gene is used to produce functional products, such as proteins. It involves the conversion of the genetic code stored in DNA into a functional molecule. This functional molecule has an important role in cellular processes.

In the process of gene expression, the first step is transcription. Transcription is the process in which genetic information encoded in DNA is converted into RNA molecule. Transcription is carried out by an enzyme called RNA polymerase. During transcription RNA polymerase binds to a specific region of DNA known as the promoter region. The promoter region contains DNA sequences that provide signals for the start of transcription. The RNA polymerase separates the DNA strands and exposes a small portion of the DNA.

Then, the RNA polymerase moves along the DNA template. The RNA polymerase moves along the DNA template strand in a three to five direction. As it moves, it adds complementary RNA nucleotides to the growing RNA strand based on the sequence of the DNA template strand. The RNA nucleotides are joined together by phosphodiester bonds. This forms an RNA molecule that is complementary to the DNA template.

Transcription continues until the RNA polymerase reaches a termination signal on the DNA template. The termination signal causes the RNA polymerase to detach from the DNA template. As a result a newly synthesized RNA molecule is released. This newly synthesized RNA molecule is called pre messenger RNA.

After transcription the pre messenger RNA undergoes further processing steps before it is ready to be translated into proteins. These processing steps are called post transcription modifications. Post transcription modifications include capping, splicing, and polyadenylation. Let us understand these modifications.

Capping is the addition of a modified nucleotide cap to the five end of the messenger RNA. The cap protects the messenger RNA from degradation by exonucleases. It has a crucial role in the recognition of messenger RNA by ribosomes to make proteins.

Polyadenylation involves the addition of a stretch of adenine nucleotides to messenger RNA to form the poly A tail. The poly A tail enhances messenger RNA stability. It protects messenger RNA from degradation. The length of the poly A tail can vary.

In eukaryotes, genes often contain non coding regions within coding regions. Non coding regions are called introns. Coding regions are called exons. Non coding regions must be removed to generate mature messenger RNA. Splicing is the process of removing introns and joining exons together to generate a mature messenger RNA molecule ready for translation.

Finally, translation occurs in the ribosomes to utilize the processed messenger RNA. Translation is the process by which the genetic information carried by messenger RNA molecules is used to synthesize proteins. It occurs in the ribosomes.

The process of translation involves the following steps. First step is called initiation. In this step, messenger RNA binds to small subunit of the ribosome. The Transfer RNA which is a type of RNA recognizes and binds to the start codon on the messenger RNA. The large subunit of the ribosome joins with the small subunit of ribosome to form translation initiation complex. Now the ribosome is assembled and ready for the elongation step.

During elongation, the ribosome slides along the messenger RNA in a specific direction, from the starting end to the ending end. As it moves, it reads the codons in messenger RNA. Each codon represents a specific amino acid.

Transfer RNA which is also a type of RNA molecules carries the corresponding amino acids to the ribosome. Transfer RNA is also called tRNA. Each tRNA molecule has a special sequence called an anticodon that matches up with the codon on the messenger RNA. The tRNA molecules bring the amino acids in the correct order and position them so that they can be joined together. The ribosome helps in linking the amino acids together by forming peptide bonds between them. As a result a growing chain of amino acids is formed. This chain is called the polypeptide chain.

Post translation modifications are chemical modifications that occur on proteins after they have been synthesized through translation. These modifications have crucial roles in regulating protein structure, function, stability, localization, and activity. There are numerous types of post translational modifications. Some of the most common include phosphorylation, glycosylation, acetylation and methylation.

During phosphorylation phosphate group is added to specific amino acid residues. During glycosylation carbohydrate molecules are added to specific amino acid residues. During acetylation, acetyl group is added to specific amino acids. During methylation, amino group is added to specific amino acids. These modifications regulate protein activity, cellular signaling, and protein-protein interactions.

We have studied that three types of RNA are involved in protein synthesis. These are messenger RNA, Transfer RNA and ribosomal RNA. Messenger RNA carries the genetic information from the DNA to the ribosomes. Its primary role is to serve as a template for protein synthesis. Transfer RNA is responsible for carrying amino acids to the ribosomes during protein synthesis. Ribosomal RNA is a component of ribosomes. Ribosomes are made up of ribosomal RNA and protein.