1. Transcription: The first step in the process is transcription, where a DNA gene is copied into a messenger RNA (mRNA) molecule. This occurs in the nucleus of the cell and involves an enzyme called RNA polymerase that reads the DNA sequence and synthesizes a complementary strand of mRNA.
2. mRNA Processing: In eukaryotic cells, the newly synthesized mRNA undergoes processing before it can leave the nucleus. This includes the removal of noncoding regions called introns, and the addition of a modified nucleotide called a 5' cap at one end and a poly-A tail at the other end. These modifications play roles in stability, transport, and translation of the mRNA.
3. mRNA Export: The processed mRNA is then exported from the nucleus into the cytoplasm through nuclear pores. Here, it can interact with the ribosomes for translation.
4. Translation: The mRNA travels to the ribosomes, which are protein synthesis factories in the cytoplasm. Translation is the process by which the mRNA is decoded to synthesize the protein. It occurs in three main steps: initiation, elongation, and termination.
5. Initiation: In this step, the small ribosomal subunit binds to the mRNA at a specific sequence called the start codon (often AUG), which marks the beginning of the protein-coding region. The tRNA (transfer RNA) carrying the corresponding amino acid, methionine, binds to this start codon.
6. Elongation: During elongation, the ribosome moves along the mRNA, reading the codons in a sequential manner. Each codon specifies a particular amino acid, and the corresponding tRNA with the matching anticodon (complementary to the codon) brings the specific amino acid to the ribosome. Peptide bonds form between the amino acids, creating a growing polypeptide chain.
7. Termination: When the ribosome reaches a stop codon (UAA, UAG, or UGA), the process of translation is terminated. Release factors recognize the stop codon and cause the ribosome to release the polypeptide chain.
8. Protein Folding: After translation, the polypeptide or protein must fold into its functional three-dimensional shape. This folding process is guided by the protein's amino acid sequence and various cellular factors, including molecular chaperones. The folded protein's structure is crucial for its proper function and interactions within the cell. Some proteins may require further modifications, such as post-translational modifications, to become fully functional.
It's important to note that this description provides a simplified overview of the process. Additional steps and factors can be involved in specific scenarios, such as protein targeting to specific cellular compartments or the regulation of gene expression.
List and describe each step in this process, starting with the gene and ending with the folded protein.
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