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Biology › Genetics And Molecular Biology

Translation Elongation and Termination: Peptide Bond Formation

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Translation Initiation: Start Codons and Ribosomal ScanningTranslation: Initiation and Elongation+2 more→→Translation Elongation and Elongation FactorsTranslation Termination and Release Factors
elongation-factors peptidyl-transferase translocase release-factors stop-codons

Core Idea

During translation elongation, aminoacyl-tRNAs are delivered to the A (acceptor) site of the ribosome by elongation factors EF-Tu (prokaryotes) or eEF1A (eukaryotes) in a GTP-dependent manner, with proofreading ensuring accuracy. The peptidyl transferase activity of the ribosome (catalyzed by 23S rRNA in prokaryotes, 28S rRNA in eukaryotes) catalyzes peptide bond formation between the carboxyl group of the P-site peptidyl-tRNA and the amino group of the A-site aminoacyl-tRNA. Elongation factors EF-G (prokaryotes) or eEF2 (eukaryotes) promote translocation, moving tRNAs and mRNA by three nucleotides (one codon), using GTP hydrolysis. Termination occurs when a stop codon (UAA, UAG, or UGA) enters the A site, recognized by release factors (RF1/RF2 in prokaryotes, eRF1/eRF3 in eukaryotes), triggering hydrolysis of the ester bond linking the polypeptide to the tRNA and dissociation of the ribosome from mRNA.

Explainer

From your study of translation initiation, you know that the ribosome assembles on mRNA with the initiator tRNA positioned in the P site, ready to begin reading codons. Elongation is the repetitive cycle that builds the polypeptide chain one amino acid at a time, and it runs with striking speed and precision — roughly 15–20 amino acids per second in bacteria. The cycle has three steps that repeat for every codon: delivery, peptide bond formation, and translocation.

In the delivery step, each new aminoacyl-tRNA arrives at the ribosome's A site as a ternary complex with the elongation factor EF-Tu (or eEF1A in eukaryotes) and GTP. Think of EF-Tu as a quality-control chaperone: it holds the charged tRNA and allows it to sample the codon in the A site. If the anticodon-codon match is correct, complementary base pairing triggers a conformational change in the ribosome that stimulates GTP hydrolysis by EF-Tu. This is the kinetic proofreading step — incorrect tRNAs dissociate before GTP hydrolysis occurs, because they lack the geometric fit needed to trigger the conformational change. The result is an error rate of roughly one misincorporation per 10,000 amino acids, far better than codon-anticodon base pairing alone could achieve.

Once the correct aminoacyl-tRNA is locked into the A site, the peptidyl transferase reaction forms the peptide bond. This is catalyzed not by a protein enzyme but by the ribosomal RNA itself — specifically the 23S rRNA (28S in eukaryotes) — making the ribosome a ribozyme. The reaction transfers the growing polypeptide chain from the P-site tRNA to the amino group of the A-site aminoacyl-tRNA, extending the chain by one residue. After peptide bond formation, the P site holds a now-empty (deacylated) tRNA and the A site holds the peptidyl-tRNA bearing the entire growing chain. The elongation factor EF-G (or eEF2) then drives translocation: using the energy of GTP hydrolysis, it ratchets the ribosome forward by exactly one codon (three nucleotides), shifting the deacylated tRNA to the E (exit) site and the peptidyl-tRNA to the P site, leaving the A site open for the next incoming aminoacyl-tRNA.

Termination breaks this cycle. When a stop codon — UAA, UAG, or UGA — enters the A site, no aminoacyl-tRNA recognizes it. Instead, protein release factors bind: in prokaryotes, RF1 recognizes UAA and UAG while RF2 recognizes UAA and UGA; in eukaryotes, a single factor eRF1 recognizes all three stop codons. The release factor mimics the shape of a tRNA, fitting into the A site and positioning a catalytic domain near the peptidyl transferase center. This triggers hydrolysis of the ester bond connecting the completed polypeptide to the final tRNA, freeing the finished protein. The ribosome then disassembles with help from ribosome recycling factor and EF-G (prokaryotes) or from eRF3 and ABCE1 (eukaryotes), releasing the mRNA and ribosomal subunits for reuse. The entire process — from initiation through hundreds or thousands of elongation cycles to termination — produces one complete polypeptide, ready for folding and post-translational modification.

Practice Questions 5 questions

Prerequisite Chain

Understanding Zero → The Number Zero → Counting to Five → Counting to 10 → Counting to 20 → Counting a Set of Objects Up to 20 → Cardinality: The Last Number Counted → Matching Numerals to Quantities → Subitizing Small Quantities → Addition Within 10 → Number Bonds to 10 → Addition Within 20 → Doubles and Near Doubles → Doubles Facts Within 10 → Near Doubles Facts Within 20 → Mental Math Strategies for Addition → Mental Math: Adding and Subtracting Tens → Addition Within 100 → Repeated Addition as Multiplication → Multiplication as Equal Groups → Multiplication: Arrays → Basic Multiplication Facts (0s, 1s, 2s, 5s, 10s) → Multiplication Facts Within 100 → Division as Equal Sharing → Division as Grouping (Measurement Division) → Division: Grouping (Repeated Subtraction) Model → Division: Fair Sharing Model → Division as Equal Sharing → Division as Grouping → Basic Division Facts → Division Facts Within 100 → Multiplication and Division Fact Families → Relationship Between Multiplication and Division → Division Facts as Inverse of Multiplication → Remainders and Quotients in Division → Division Word Problems → Multi-Step Word Problems → Solving Multi-Step Word Problems → Multiplication Word Problems → Division Word Problems → Introduction to Long Division → Factors and Multiples → Prime and Composite Numbers → Equivalent Fractions → Relating Fractions and Decimals → Decimal Place Value → Integers and the Number Line → Comparing and Ordering Integers → Absolute Value → Adding Integers → Subtracting Integers → Multiplying Integers → Dividing Integers → Unit Rates → Proportions → Percent Concept → Converting Between Fractions, Decimals, and Percents → Operations with Rational Numbers → Two-Step Equations → Solving Multi-Step Equations → Equations with Variables on Both Sides → Angle Pairs: Complementary, Supplementary, and Vertical → Parallel Lines and Transversals → Corresponding Angles → Alternate Interior Angles → Triangle Angle Sum Theorem → Exterior Angle Theorem → Triangle Inequality Theorem → Similar Triangles: AA Similarity → Similar Triangles: SSS and SAS Similarity → Proportions in Similar Triangles → Right Triangle Trigonometry Introduction → Sine, Cosine, and Tangent Ratios → Trigonometric Ratios Review → Radian Measure → Converting Between Degrees and Radians → The Unit Circle → Graphing Sine and Cosine → Graphing Tangent and Reciprocal Trigonometric Functions → Derivatives of Trigonometric Functions → Antiderivatives → Indefinite Integrals → Basic Integration Rules → Riemann Sums → Definite Integral Definition → Double Integrals: Definition and Setup → Iterated Integrals and Fubini's Theorem → Double Integrals over Rectangular Regions → Double Integrals over General Regions → Applications of Double Integrals: Area, Mass, and Moments → Triple Integrals in Cartesian Coordinates → Triple Integrals in Cylindrical and Spherical Coordinates → Change of Variables and the Jacobian Determinant → Applications of Triple Integrals: Volume and Mass → Vector Fields and Their Representations → Line Integrals of Vector Fields → Work and Circulation → Line Integrals of Scalar and Vector Functions → Fundamental Theorem for Line Integrals → Conservative Vector Fields → Conservative Vector Fields and Potential Functions → Curl and Divergence of Vector Fields → Curl and Divergence → Divergence Theorem → Electric Flux and Divergence Theorem → Gauss's Law: Integral Form and Meaning → Solving Problems with Gauss's Law → Conductors in Electrostatic Equilibrium → Capacitance and Capacitors → Dielectrics → Dielectric Constant and Relative Permittivity → Electric Field Inside Dielectric Materials → Dielectric Materials and Polarization → Dielectric Susceptibility and Permittivity → Energy Density in Electric Fields → Electric Current and Current Density → Electrical Resistance and Resistivity → Ohm's Law and Circuit Elements → Electromotive Force (EMF) and Batteries → Kirchhoff's Circuit Laws: Voltage and Current → DC Circuit Network Analysis Methods → Transient Response in RC Circuits → RC Circuits → LC and RLC Circuits → AC Circuits: Fundamentals → Impedance and Reactance → AC Power and Resonance → Electromagnetic Waves → Postulates of Special Relativity → Time Dilation → Length Contraction → Lorentz Transformation → Relativistic Velocity Addition → Relativistic Momentum and Energy → Mass-Energy Equivalence and E=mc² → Photons as Particles with Energy and Momentum → Planck-Einstein Relation: Energy and Frequency → Photoelectric Effect → The Photon: Light as Quanta → Compton Scattering → Wave-Particle Duality → de Broglie Wavelength → The Schrödinger Equation → State Vectors and Wavefunctions → Quantum Superposition → Quantum Entanglement → Bell Theorem and Bell Inequalities → Postulates of Quantum Mechanics → Observables and Quantum Operators → Commutators and Commutation Relations → Quantum Angular Momentum → Quantum Mechanical Treatment of Hydrogen → Solving the Schrödinger Equation for Hydrogen Atom → Quantum Numbers → Electron Configuration → Periodic Trends → Covalent Bonding → Electronegativity and Bond Polarity → Ionic Bonding → Lewis Structures → VSEPR Theory and Molecular Geometry → Molecular Geometry and Electron Pair Geometry → Molecular Polarity and Dipole Moments → Intermolecular Forces → States of Matter and Phase Changes: Melting, Boiling, and Sublimation → Gas Laws and the Ideal Gas Equation → Gas Stoichiometry and Volume-Volume Calculations → Thermochemistry and Enthalpy → Heat Capacity and Calorimetry → Entropy and Molecular Disorder → Spontaneity and ΔG → Entropy and Gibbs Free Energy → Chemical Equilibrium → Acid-Base Chemistry → Weak Acid Ionization → Weak Base Ionization → Acid and Base Strength: Ka, Kb, and Ionization → Leaving Groups and Nucleofugality → SN2 Substitution Reactions → SN1 Substitution Reactions → E1 Elimination Reactions → Alcohols and Ethers: Structure, Properties, and Nomenclature → Reactions of Alcohols → Aldehydes and Ketones: Structure and Reactivity → Oxidation Reactions in Organic Chemistry → Oxidation of Alcohols to Aldehydes and Ketones → Aldehyde and Ketone Structure and Nomenclature → Nucleophilic Addition to Aldehydes and Ketones → Carboxylic Acids and Their Derivatives → IUPAC Nomenclature of Carbonyls and Carboxylic Acids → IUPAC Nomenclature of Alkenes → Electrophilic Addition to Alkenes → Aromaticity and Benzene → Electrophilic Aromatic Substitution (EAS) → Nucleophilic Aromatic Substitution (SNAr) → Nucleophilic Acyl Substitution → Amines: Structure, Basicity, and Reactions → Amine Reactivity: Nucleophilicity and Basicity → Amino Acid Structure and Properties → Peptide Bonds and Polypeptide Formation → Protein Primary Structure → Protein Secondary Structure → Protein Tertiary Structure → Enzyme Structure and Function → Transcription: DNA to RNA → RNA Types and Structure → RNA Structure and Intramolecular Base Pairing → RNA Processing and Splicing → Translation: RNA to Protein → Ribosomes: Protein Synthesis Machines → Translation: Initiation and Elongation → Translation Initiation: Start Codons and Ribosomal Scanning → Translation Elongation and Termination: Peptide Bond Formation

Longest path: 213 steps · 1095 total prerequisite topics

Prerequisites (4)

Translation: Initiation and Elongationhard Translation Initiation: Start Codons and Ribosomal Scanninghard Ribosomal RNA as a Ribozyme and Ribosome Assemblysoft The Genetic Code: Reading Frame and Wobble Base Pairingsoft

Leads To (2)

Translation Elongation and Elongation Factorssoft Translation Termination and Release Factorssoft