transcription. During transcription, the DNA strand containing the gene unravels and the enzyme RNA polymerase binds to the starting point of the gene. The RNA polymerase moves along the DNA strand, reading the nucleotide sequence and constructing a complementary strand of messenger RNA (mRNA). This process is called transcription because it converts the DNA gene sequence into an mRNA sequence.
The next step is mRNA processing. The initial mRNA transcript produced during transcription contains both exons (coding regions) and introns (non-coding regions). The introns have to be removed and the exons connected together to form the final mRNA molecule. This process is called splicing. Certain RNA molecules, called small nuclear RNA (snRNA) and a complex of proteins, form a spliceosome and recognize specific splice sites on the mRNA transcript. The spliceosome cuts out the introns and connects the exons together, generating a mature mRNA molecule.
After mRNA processing, the mature mRNA molecule leaves the nucleus and enters the cytoplasm for translation. Translation is the process where the mRNA molecule is utilized to synthesize a specific protein. The mRNA molecule serves as a template for the production of the protein. The process begins with the mRNA molecule binding to a ribosome. Ribosomes consist of two subunits (small and large) that come together and attach to the mRNA molecule.
During translation, the ribosome moves along the mRNA molecule in a process called elongation. As the ribosome moves, it reads the codons (groups of three nucleotides) on the mRNA molecule. Each codon corresponds to a specific amino acid. Transfer RNA (tRNA) molecules carry the respective amino acids and bind to the appropriate codon on the mRNA molecule, forming peptide bonds between the amino acids and creating a growing polypeptide chain. This process continues until a stop codon is reached, signaling the end of translation.
Once translation is complete, the newly synthesized polypeptide chain undergoes post-translational modifications. These modifications can include folding of the protein into its three-dimensional structure, addition of chemical groups (e.g., phosphorylation or glycosylation), or cleavage of certain parts of the protein. These modifications are important for the protein to function properly.
The final step is the formation of the folded protein. The newly synthesized polypeptide chain folds into its three-dimensional structure through a process called protein folding. Folding is assisted by various cellular factors called chaperones, which help guide the polypeptide into its correct shape. The folded protein is then ready to carry out its specific function in the cell.