Question

Explain the process of formation of complex proteins.

Answer 1

The synthesis of proteins occurs according to the central dogma. The central dogma explains how genetic information flows from DNA to RNA to make a functional protein. It suggests that DNA contains all the information required to synthesise a protein and the RNA acts as a messenger which carries this information to ribosomes (a type of cell organelle). The central dogma is represented as:

Transcription: Transcription results in the formation of an mRNA using DNA as a template. This process takes place in the nucleus. You must be aware that DNA is made up of two strands. But in this process only one strand of DNA is required and this one strand is used as the template for the synthesis of the mRNA.

An enzyme, RNA polymerase, helps in this process. It helps in copying the information from DNA strand to mRNA. Once this process is complete, the RNA polymerase dissociates from the strand and the newly synthesised mRNA is released from the nucleus. Like DNA, RNA is also made up of nucleotides but there is a difference. RNA contains the nucleotide Uracil (U) instead of thymine which is present in DNA. This uracil pairs with adenine just like thymine.
Once the process of transcription is complete, the newly synthesised mRNA is released from the nucleus into the cytoplasm.

Translation: The newly synthesised mRNA contains information in the form of codons. A codon is a sequence of 3 DNA or RNA nucleotides that correspond with a specific amino acid. Since, these codons contain 3 nucleotides, they are called triplet codons.

Process of translation:

• After the mRNA is released into the cytoplasm, it reaches the ribosomes where the process of translation occurs. Each mRNA can be made up of thousands of triplet codons.
• Two other types of RNAs, i.e. tRNA and rRNA, also participate in this process.
• Each tRNA has an anticodon which has a sequence complementary to the codon on mRNA. These tRNAs supply the amino acids as per the codons on the mRNA.
• The amino acids which are brought by the tRNA are joined together by peptide bonds. This process is carried out with the help of rRNA.
• During this process, the ribosome moves from one end of the mRNA to the other by a process known as translocation.

At the end of this process a protein is formed which undergoes further modifications to form a fully functional protein.