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Translation in Eukaryotes.
This document summarizes the process of translation. Translation is the process by which the sequence of nucleotides in messenger RNA directs the incorporation of amino acids into a protein. It involves three main steps - initiation, elongation, and termination. Initiation requires various initiation factors and ribosomal subunits to form the initiation complex. Elongation is a cyclic process of aminoacyl-tRNA binding, peptide bond formation, and translocation. Termination occurs when a stop codon is reached, releasing the polypeptide chain. Ribosomal recycling then dissociates the post-termination complex to prepare the ribosome for another round of translation.
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Introduction to translation as protein synthesis; converting mRNA sequence into amino acids.
Four key components of translation: mRNA, tRNA, enzymes, and ribosomes for protein synthesis.
Overview of the translation process with three steps: initiation, elongation, and termination.
Complex initiation in eukaryotes involves factors and steps leading to 80S initiation complex formation.
Elongation of polypeptide chain through the addition of amino acids, involving binding, bond formation, and translocation.
Translation termination occurs at stop codons, involves release factors, and frees the polypeptide product.
Ribosomal recycling involves releasing mRNA and tRNA, allowing ribosome to dissociate for new synthesis.
Gratitude expressed for attention.
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Translation in Eukaryotes.
- 1. TRANSLATION Anushi Jain MSc I RollNo. : 12 Paper III
- 2. INTRODUCTION • Translation isbasically a synonym process of protein synthesis. • It is the process in which the protein is synthesized from the information contained in a molecule of messenger RNA (mRNA). • It can defined as “ the process by which the sequence of nucleotides in a messenger RNA molecule directs the incorporation of amino acid into protein.”
- 3. TRANSLATIONAL MACHINERY • Themachinery required for translating the language of messenger RNAs into the language of proteins is composed of four primary components • mRNAs : Messenger RNA (mRNA) provides an intermediate that carries the copy of a DNA sequence that represents protein • tRNAs : tRNA acts as an adaptor between the codons and the amino acids they specify. • Enzymes : Required for the attachment of amino acids to the correct tRNA molecule. i. Aminoacyl-tRNA Synthetase. ii. Peptidyl Transferase. • Ribosome : It is the macromolecular complex that directs the synthesis of proteins.
- 4. TRANSLATION PROCESS • Ina prokaryotic cell, transcription and translation are coupled; that is, translation begins while the mRNA is still being synthesized. In a eukaryotic cell, transcription occurs in the nucleus, and translation occurs in the cytoplasm. • Translation involves three major steps : 1. INITIATION 2. ELONGATION 3. TERMINATION
- 5. 1. INITIATION The initiationof translation in eukaryotes is complex, involving at least 10 eukaryotic initiation factors (eIFs) & divided into 4 steps : a. Ribosomal dissociation. b. Formation of 43S preinitiation complex. c. Formation of 48S initiation complex. d. Formation of 80S initiation complex.
- 6. a. Ribosomal Dissociation •The 80S ribosome dissociates to form 40S & 60S subunits. • Two initiating factors namely elF-3 & elF-1A bind to the newly formed 40S subunit & thereby block its reassociation with 60S subunit.
- 7. b. Formation Of43S Preinitiation Complex • A ternary complex containing met-tRNA′ & elF-2 bound to GTP attaches to 40S ribosomal subunit to form 43S preinitiation complex. • The presence of elF-3 & elF-1A stabilizes this complex.
- 8. c. Formation Of48S Initiation Complex • The binding of mRNA to 43S preinitiation complex results in the formation of 48S initiation complex through the intermediate 43S initiation complex. • elF-4F complex is formed by the association of elF-4G, elF-4A with elF-4E. • The elF-4F (referred to as cap binding protein) binds to the cap of mRNA.
- 9. • Then elF-4A& elF-4B bind to mRNA & reduce its complex structure. • This mRNA is then transferred to 43S complex. • For the appropriate association of 43S preinitiation complex with mRNA, energy has to be supplied by ATP. • The ribosomal initiation complex scans the mRNA for the identification of appropriate initiation codon. • 5'-AUG is the initiation codon.
- 10. d. Formation Of80S Initiation Complex • 48S initiation complex binds to 60S ribosomal subunit to form 80S initiation complex. • The binding involves the hydrolysis of GTP (bound to elF- 2). • This step is facilitated by the involvement of elF-5. • As the 80S complex is formed, the initiation factors bound to 48S initiation complex are released & recycled.
- 12. 2.ELONGATION • Ribosomes elongatethe polypeptide chain by a sequential addition of amino acids. • The amino acid sequence is determined by the order of the codons in the specific mRNA. • Elongation, a cyclic process involving certain elongation factors (EFs). • Elongation may be divided into three steps. a. Binding of Aminoacyl t-RNA to A-site. b. Peptide bond formation. c. Translocation.
- 13. a. Binding ofAminoacyl t-RNA to A- site • The 80S initiation complex contains met tRNA′ in the P- site & A-site is free. • Another Aminoacyl-tRNA is placed in the A-site. • This requires proper codon recognition on the mRNA & involvement of elongation factor 1a (EF-1a) & supply of energy by GTP. • The Aminoacyl-tRNA is placed in the A-site, EF-1a & GDP are recycled to bring another Aminoacyl-tRNA.
- 14. b. Peptide bondformation • The enzyme Peptidyl transferase catalyzes the formation of peptide bond. • The activity of this enzyme lies on 28S RNA of 60S ribosomal subunit. • It is therefore the rRNA (and not protein) referred to as ribozyme that catalyzes peptide bond formation. • Net result of peptide bond formation is the attachment of the growing peptide chain to the tRNA in the A-site.
- 15. c. Translocation • Theribosome moves to the next codon of the mRNA (towards 3'-end). • This process called translocation, involves the movement of growing peptide chain from A-site to P-site. • Translocation requires EF-2 & GTP. • GTP gets hydrolyzed and supplies energy to move mRNA. • EF-2 & GTP complex recycles for translocation. • About six amino acids per second are incorporated during the course of elongation of translation in eukaryotes.
- 17. 3. TERMINATION • Oneof the stop or termination signals (UAA, UAG and UGA) terminates the growing polypeptide. • When the ribosome encounters a stop codon, - there is no tRNA available to bind to the A site of the ribosome, - instead a release factor binds to it. • In eukaryotes, a single release factor- eukaryotic release factor 1 (eRF1)-recognizes all three stop codons, and eRF3 stimulates the termination events. • once the release factor binds, the ribosome unit falls apart, - releasing the large and small subunits, - the tRNA carrying the polypeptide is also released, freeing up the polypeptide product. • Ribosome recycling occurs in eukaryotes.
- 18. RIBOSOMAL RECYCLING • Afterthe release of polypeptide and the release factors the ribosome is still bound to the mRNA and is left with two deacylated tRNA (in the P and E sites). • To participate in a new round of polypeptide synthesis, these mRNA and the tRNA must be released and the ribosome must dissociate into small subunit and large subunit. • Collectively these events are termed as ribosome recycling
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