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The standard method of protein production or protein synthesis includes two parts: protein transcription and protein translation. Protein transcription makes a ribonucleic acid (RNA) copy of a gene that carries the blueprint to make the needed protein. In protein translation, the RNA is used to make a protein using amino acid building blocks. Bacteria, which are prokaryotes, produce protein with a simpler method that involves no post-transcription or post-translation changes. More complex animals, such as humans, are eukaryotes and make modifications to RNA and proteins during protein production.
Protein transcription takes place in the nucleus of a cell, where the deoxyribonucleic acid (DNA) is contained. DNA is the genetic or hereditary part of a cell, and the genes that it contains command the proteins that are then produced in the cell. During transcription, a DNA gene is used to make messenger RNA (mRNA), which is an RNA copy. RNA polymerase, an enzyme, does the transcription.
The process of protein translation is performed in the cytoplasm of the cell, which is everything in the cell outside of the nucleus. In translation, the mRNA copy of a gene is used to add amino acids in the correct order to make the protein. Translation uses a structure called a ribosome to produce proteins.
The mRNA contains codons, each of which codes for one of the 20 amino acids. The ribosome sandwiches the mRNA. Transfer RNA (tRNA) is used to bring in a new amino acid that matches with the exposed codon in the mRNA. Then, everything shifts, a new codon is available, and a new tRNA brings in the next amino acid. This continues until a stop codon is reached, indicating that the protein is completely produced.
There is as easy way for one to remember which methods of protein production do what. To transcribe something is to copy it. DNA and RNA are very similar molecules, so to take DNA and make an RNA copy would be to transcribe, so this step is called transcription.
To translate is to take one language and decipher it into another language. RNA and proteins are made with different building blocks and thus are very different molecules. There's a universal genetic code that is used to translate what is in the RNA into the amino acid building blocks of a protein, so turning RNA into protein is called translation.
Eukaryote cells, which include most animals from yeast to humans, make both post-transcription and post-translation modifications during protein production. Post-transcription changes involve a process called splicing, which is needed to make a functional mRNA molecule. A pre-mRNA transcript contains two parts, exons that are necessary for the second step of protein production and introns that are not needed. In splicing, the introns are cut out, and the exons are rejoined together. During splicing, exons also can be rearranged from one gene to create different proteins.
Post-translation modifications involve helping the protein fold as well as properly directing the protein in the cell. Often, a protein begins with what is called a signal peptide. This signal peptide acts like an address to direct the protein where it's needed in the cell and is then usually removed after the protein gets to its designation. Most eukaryote proteins cannot, on their own, fold into their specific three-dimensional shapes. Chaperon proteins then help proteins fold into functional molecules.
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