page_title: Protein biosynthesis
section_title: Translation
hierarchical_section_title: Protein biosynthesis / Translation
caption_attribution_description: English: Animation of Translation: The elongation and membrane targeting stages of eukaryotic translation. The ribosome is green and yellow, the tRNAs are dark blue, and the other proteins involved are light blue. The produced peptide is released into the endoplasmic reticulum.Shape of the ribosom computed with something like Quantum Monte Carlo. Deutsch: Animation der Translation: Das Ribosom ist grün and gelb, tRNA dunkelblau, andere involvierte Proteine hellblau. Das entstandene Peptid wird in das Endoplasmatisches Retikulum entlassen.Gestalt des Ribosoms vielleicht mittels Quantum Monte Carlo berechnet. Español: Traducción Français&#160;: Traduction génétique: Le ribosome est vert et jaune, les ARNt sont bleu foncé, et les autres protéines impliquées bleu clair, réticulum endoplasmique gris. 日本語: 翻訳 (生物学) 한국어: 번역 (생물학) Nederlands: Translatie עברית: תרגום: הריבוזום ותהליך התרגום. הסרט המתארך מעלה מתוך הריבוזום הוא המבנה הראשוני של החלבון המתורגם. הסרט המתקדם שמאלה הוא ה-mRNA. בכחול כהה, tRNA, ובכחול בהיר חלבונים: החלבון הנושא את ה-tRNA הוא EF-Tu . החלבון ש"דוחף" את ה- tRNA לאחר מיקומו בריבוזום הוא EF-G .חלקה השני של האנימציה מתאר את תהליך העברת הריבוזום לאזור הרשתית התוך-פלזמית, בעזרת ה- SRP (Signal_recognition_particle), הנקשר לרצפטור מתאים (Signal recognition particle receptor) על הרשתית. Magyar: Transzláció: A Riboszóma sárga és zöldben, transzfer RNS sötétkékben, más fehérjék világoskékben; membrán és Hírvivő RNS feketében, Endoplazmatikus retikulum a belsője szürkében. Português: Tradução Русский: Трансляция 中文: 翻譯 (生物學)
context_page_description: Protein biosynthesis is a core biological process, occurring inside cells, balancing the loss of cellular proteins through the production of new proteins. Proteins perform a variety of critical functions as enzymes, structural proteins or hormones and therefore, are crucial biological components. Protein synthesis is a very similar process for both prokaryotes and eukaryotes but there are some distinct differences.
  Protein synthesis can be divided broadly into two phases - transcription and translation. During transcription, a section of DNA encoding a protein, known as a gene, is converted into a template molecule called messenger RNA. This conversion is carried out by enzymes, known as RNA polymerases, in the nucleus of the cell. In eukaryotes, this messenger RNA is initially produced in a premature form which undergoes post-transcriptional modifications to produce mature mRNA. The mature mRNA is exported from the nucleus via nuclear pores to the cytoplasm of the cell for translation to occur. During translation, the mRNA is read by ribosomes which use the nucleotide sequence of the mRNA to determine the sequence of amino acids.
context_section_description: During translation, ribosomes synthesise polypeptide chains from mRNA template molecules. In eukaryotes, translation occurs in the cytoplasm of the cell, where the ribosomes are located either free floating or attached to the endoplasmic reticulum. In prokaryotes, which lack a nucleus, the processes of both transcription and translation occur in the cytoplasm.
  Ribosomes are complex molecular machines, made of a mixture of protein and ribosomal RNA, arranged into two subunits (a large and a small subunit), which surround the mRNA molecule. The ribosome reads the mRNA molecule in a 5'-3' direction and uses it as a template to determine the order of amino acids in the polypeptide chain. In order to translate the mRNA molecule, the ribosome uses small molecules, known as transfer RNAs (tRNA), to deliver the correct amino acids to the ribosome. Each tRNA is composed of 70-80 nucleotides and adopts a characteristic cloverleaf structure due to the formation of hydrogen bonds between the nucleotides within the molecule. There are around 60 different types of tRNAs, each tRNA binds to a specific sequence of three nucleotides (known as a codon) within the mRNA molecule and delivers a specific amino acid.
  The ribosome initially attaches to the mRNA at the start codon (AUG) and begins to translate the molecule. The mRNA nucleotide sequence is read in triplets - three adjacent nucleotides in the mRNA molecule correspond to a single codon. Each tRNA has an exposed sequence of three nucleotides, known as the anticodon, which are complementary in sequence to a specific codon that may be present in mRNA. For example, the first codon encountered is the start codon composed of the nucleotides AUG. The correct tRNA with the anticodon (complementary 3 nucleotide sequence UAC) binds to the mRNA using the ribosome. This tRNA delivers the correct amino acid corresponding to the mRNA codon, in the case of the start codon, this is the amino acid methionine. The next codon (adjacent to the start codon) is then bound by the correct tRNA with complementary anticodon, delivering the next amino acid to ribosome. The ribosome then uses its peptidyl transferase enzymatic activity to catalyse the formation of the covalent peptide bond between the two adjacent amino acids.
  The ribosome then moves along the mRNA molecule to the third codon. The ribosome then releases the first tRNA molecule, as only two tRNA molecules can be brought together by a single ribosome at one time. The next complementary tRNA with the correct anticodon complementary to the third codon is selected, delivering the next amino acid to the ribosome which is covalently joined to the growing polypeptide chain. This process continues with the ribosome moving along the mRNA molecule adding up to 15 amino acids per second to the polypeptide chain. Behind the first ribosome, up to 50 additional ribosomes can bind to the mRNA molecule forming a polysome, this enables simultaneous synthesis of multiple identical polypeptide chains. Termination of the growing polypeptide chain occurs when the ribosome encounters a stop codon (UAA, UAG, or UGA) in the mRNA molecule. When this occurs, no tRNA can recognise it and a release factor induces the release of the complete polypeptide chain from the ribosome.
caption: Demonstrates the action of the ribosome as a biological machine which functions on a nanoscale to perform translation. The ribosome moves along the mature mRNA molecule incorporating tRNA and producing a polypeptide chain.