The first step of protein synthesis is transcription. Transcription begins with a regular double helix DNA. RNA polymerase binds to the promoter and moved across the strand untwining the double helix into a coding and template strand. RNA polymerase continues to move across the DNA strand in the 3 prime to 5 prime direction, adding complementary MRNA bases. The MRNA bases are still nucleotides but they use Uracil instead of thymine. After RNA polymerase has coded it detaches from the RNA and has now produced PreMRNA. Pre MRNA was produced from a segment of the DNA called the transcription unit. Transcription occurs in the nucleus, but before the MRNA can leave the nucleus it must be processed further.
RNA processing occurs only in eukaryotes, because prokaryotes do not have a nucleus in which they can be further processed. RNA processing is important because there are certain parts of the MRNA that do not code for the polypeptide. The ends of the MRNA do not code for the polypeptide. Therefore, a five cap of modified guanine is attached to the 5 prime end and a poly-a-tail with 30-200 adenine bases is attached to the 3 prime ends. Small nuclear ribonucleoproteins, also known as SNURPS combine with other proteins to form spleicosomes in order to remove the introns (noncoding portion of MRNA and this is the end of RNA processing and the Pre MRNA is now MRNA.
The final step of protein synthesis is translation. The general idea of this step is that MRNA enters the ribosome and puts together its codons with anticodons in the five prime to three prime order. The TRNA helps to do this, and when translation is over, you have a polypeptide sequence. For a more in depth look at translation, you begin with you MRNA strand and it enters the ribosome and attaches to the ribosomal subunit. TRNA then enters the ribosome with the anticodon that connects to the AUG, and when this occurs the amino acid Methionine is produced. A large ribosomal subunit (which is made of ribosomal RNA) comes in with a P site, and an A site, and the Methionine amino acid is currently located in the P site. TRNA enters again and produces an anticodon for the MRNA. These two amino acids are then connected by a peptide bond. The TRNA with the next amino acid is currently in the A site. The mRNA strand then shifts over and the Methionine amino acid leaves the ribosome through the E (exit) site and the next amino acid moves to the P site leaving room for another TRNA to enter the A site and create a polypeptide with its anticodon. This process occurs until a stop codon is found and then the release protein frees the completed polypeptide chain. Translation is divided into three steps, initiation, elongation, and termination. Initiation is when the TRNA anticodon creates a Methionine amino acid. Elongation occurs as the proteins move from the A site to the P site, to the E site, and the polypeptide chain gets longer. Termination occurs when the UAA, UAG, or UGA codon is located and the release protein releases the completed polypeptide from the ribosome.
The types of RNA in the final step of protein synthesis are extremely important for the production of proteins. Protein synthesis begins with DNA, which is a nucleotide sequence, without the creation of mRNA, the DNA sequence could not be translated properly, and the Thymines would not change to Uracil, which is a very important step for the TRNA to work properly. TRNA is also very important because it translates the DNA nucleotide sequence into an amino acid sequence, so that it can actually become a protein. RRNA is also important, because it is what the large ribosomal subunit is made of, and translation would not be possible without it.
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