Over the last two units, we have looked at the processes by which the information coded on
a piece of DNA (gene) is used to make a functional protein. List and describe each step in this
process, starting with the gene and ending with the folded protein.
The process by which the information coded on a piece of DNA (gene) is used to make a functional protein involves several steps. Here is a list and description of each step in this process:
1. Transcription: The first step is transcription, where the DNA sequence of the gene is copied into a complementary RNA molecule called messenger RNA (mRNA). This process takes place in the nucleus of the cell and involves an enzyme called RNA polymerase.
2. RNA Processing: The mRNA undergoes processing before it leaves the nucleus. This includes the removal of non-coding regions called introns and the addition of a protective cap and a poly-A tail. These modifications help in stabilizing the mRNA and facilitating its translation in the cytoplasm.
3. mRNA Export: Once processed, the mRNA is transported out of the nucleus and into the cytoplasm through nuclear pores. This allows the mRNA to reach the site of protein synthesis in the cytoplasm.
4. Translation: In the cytoplasm, the mRNA binds to a ribosome, which serves as the site of protein synthesis. Translation begins with the binding of a specific specialized RNA molecule called transfer RNA (tRNA), which carries an amino acid that corresponds to a specific codon on the mRNA.
5. Elongation: During elongation, the ribosome moves along the mRNA molecule, reading the codons, and bringing in the appropriate tRNA molecules that match the codons. The ribosome then joins the amino acids carried by the tRNA molecules together, forming a growing polypeptide chain.
6. Termination: When the ribosome reaches a stop codon on the mRNA, translation is terminated. At this point, the ribosome releases the newly formed polypeptide chain.
7. Protein Folding: The polypeptide chain, or the newly synthesized protein, then undergoes a process known as protein folding. During this process, the protein assumes its three-dimensional shape dictated by its amino acid sequence. Protein folding is facilitated by chaperone proteins that help guide the folding process and prevent misfolding or aggregation.
8. Post-Translational Modifications: After folding, the protein can undergo various post-translational modifications, such as phosphorylation, glycosylation, or cleavage of specific regions. These modifications can alter the protein's function, stability, or localization within the cell.
9. Protein Transport: In some cases, the folded protein needs to be transported to a specific organelle or compartment within the cell. This process involves the participation of various transport proteins and signal sequences present in the protein's structure.
10. Protein Function: Finally, the folded and properly modified protein is ready to carry out its specific function within the cell. This can include enzymatic activity, structural support, regulation of gene expression, or participation in various cellular processes.
Overall, this process, known as the central dogma of molecular biology, ensures the accurate translation of genetic information from DNA to protein, allowing cells to synthesize the proteins needed for their structure and function.