TRANSLASI (BIOMOLEKULER)

TRANSLASI

            Translation is the process of translating the genetic code of the tRNA into a sequence of amino acids that make up a polypeptide or protein.

RNA processing

            When compared with the transcription, translation is a process that is more complicated because it involves the function of various macromolecules. Because most of these macromolecules present in large amounts in the cell, then the system of machine translation into the main part of each cell metabolism. Macromolecules which have a role in the translation process include:
A. More than 50 polypeptides as well as 3 to 5 molecules of ribosomal RNA in each
2. At least 20 different aminoacyl-tRNA synthetase enzymes that will activate the amino acid
3. Forty to 60 different tRNA molecules
4. At least nine soluble proteins involved in the initiation, elongation, and termination
polypeptide.

            Translational, or substantially the synthesis of protein, takes place in the ribosome, a structure that is widely available organelles in the cytoplasm. The ribosome consists of two subunits, large and small, that will converge during translation initiation and separately the translation has been completed. Translation into three stages (the same as in transcription), namely initiation, elongation, and termination. All these stages require protein factors that help mRNA, tRNA, and ribosomes during the translation process. Polypeptide chain initiation and elongation also requires a certain amount of energy. This energy is provided by GTP (guanosine triphosphat), a molecule similar to ATP.


A. Initiation

            Initiation phase is due to the three components of the mRNA, a tRNA containing the first amino acids of the polypeptide, and the two ribosomal subunits.

            An mRNA molecule would be bound to the surface of the ribosome that both subunitnya have joined. This occurs because the binding of prokaryotic mRNA are specific base sequences are known as the ribosome binding site (ribosome binding site) or a Shine-Dalgarno sequence. Meanwhile, on the eukaryotic ribosome binding by the 5 'end of mRNA. Furthermore, a variety of aminoacyl-tRNA will arrive one by one to the ribosome-mRNA complex in the order in accordance with the anticodon and amino acid it carries. This sequence is determined by the sequence of triplet codons in the mRNA. Peptide bond is formed between the amino acids that are strung into a polypeptide chain on the ribosome P site.

            The incorporation of amino acids because the amino group in amino acids that are new to the carboxyl group bonded to the amino acids contained in the polypeptide chain is extended. mRNA from the nucleus to the cytoplasm out accosted by ribosomes, and mRNA into the "gap" in the ribosome. When the mRNA into the ribosome, the ribosome "reads" the codons that enter. Readings made for each of three bases to complete the whole sequence. For the record came to mebaca ribosome codon is usually not just one but several ribosomes are known as puncture polisom form a series of similar one, in which the plug is the "mRNA" and the meat is "ribosomnya".

            Padaumumnya an mRNA will be translated simultaneously by multiple ribosomes to each other within about 90 bases along the mRNA molecule. Translation complex consisting of an mRNA and a ribosome is called poliribosom or polisom. Polisom magnitude is highly variable and correlated with the size of the polypeptide to be synthesized. For example, hemoglobin chains composed of about 150 amino acids were synthesized by polisom consisting of five pieces of the ribosome (pentaribosom).

            Thus, codon reading process can take place in sequence. When I read the ribosome codon (ie AUG kodonnya), tRNA anticodon UAC and carrying the amino acid methionine to come. tRNA into the ribosome gap. Here ribosomes serve to facilitate the attachment of a specific tRNA anticodon with the mRNA codons during protein synthesis. Ribosomal subunits constructed by protein-protein and ribosomal RNA molecules.

2. Elongation

            In the elongation phase of translation, amino acids, amino acids are added one by one in the first amino acid (methionine). MRNA to the ribosome continues to shift more sense, in order to read the codon II. For example, codons UCA II, which immediately means that codons translated by tRNA AGU carrying the amino acid serine. In the ribosome, the first methionine into serine coupled to form a dipeptide.

            The ribosome continues to shift, reading codons III. Suppose III GAG codon, immediately translated by the CUC anticodon carrying the amino acid glycine. tRNA into the ribosome. Amino acid glycine dipeptide coupled with an already formed so as to form tripeptida. So forth the process of reading the genetic code took place in the ribobom, which translated into amino acids to be assembled into a polypeptide.

            MRNA codon on the ribosome to form hydrogen bonds with the anticodon of tRNA molecules that carry incoming amino acid is right. MRNA molecules of amino acids that have been released to return to the cytoplasm for transport of the amino acid repeat. RRNA molecule of the large ribosomal subunit function as enzymes, which catalyze the formation of peptide bonds that incorporate polypeptide that extends to the newly arrived amino acids. Polypeptide chain elongation or elongation will continue until a tripet termination codons that encode into site A.

            Before a completed polypeptide chain is synthesized in the first place deformilisasi f-methionine into methionine. Termination is marked by the release of mRNA, tRNA in the P site, and the polypeptide chain from the ribosome. In addition, both subunits of ribosomes were split. At the termination of the activity of two proteins required that acts as a releasing factor or releasing factors, namely RF-1 and RF-2.

3. Termination

            The final stage is the translational termination. Elongation continues until the ribosome reaches the stop codon. Base triplet stop codon is UAA, UAG, and UGA. No stop codon encodes an amino acid but act in a signal to stop translation. Polypeptide formed then "processed" into protein.

Differences in prokaryotic and eukaryotic translation.


            In the prokaryotic translation often begins before transcription ends. This is possible due to the absence of a wall that separates the nucleus of transcription and translation. Proceeds both processes simultaneously, the expression of genes to be very fast and the mechanism of flame-off (turn off onturn) gene expression, as will be explained later, also became very efficient. However, it is not the case in eukaryotes. Transcription occurs in the nucleus, whereas translation occurs in the cytoplasm (ribosomes).