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Translation Elongation and Elongation Factors

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Ribosomal Initiation Factors and Initiator tRNA Translation Elongation and Termination: Peptide Bond Formation→→Translation Termination and Release Factors

Core Idea

During elongation, EF-Tu (prokaryotes) or eEF1A (eukaryotes) delivers aminoacyl-tRNA to the ribosomal A site in a GTP-dependent manner. GTP hydrolysis occurs upon correct codon-anticodon pairing (proofreading step). EF-G (prokaryotes) or eEF2 (eukaryotes) then catalyzes translocation of tRNAs and mRNA, advancing the ribosome by one codon.

How It's Best Learned

Use cryo-EM structures or animations to visualize the three-site model of the ribosome (A, P, E). Trace the movement of tRNAs and mRNA through successive cycles. Understand how GTP hydrolysis provides energy and ensures fidelity.

Common Misconceptions

Assuming elongation is a single step when it involves multiple distinct phases (A/T binding, proofreading, translocation).
Not recognizing that the ribosome actively discriminates against cognate codons through induced-fit proofreading.
Thinking elongation factors bind permanently to the ribosome when they associate and dissociate with each cycle.

Explainer

From your study of translation initiation, you know that the ribosome assembles on the mRNA with the initiator tRNA positioned in the P site (peptidyl site), base-paired with the start codon. The A site (aminoacyl site) is empty and ready to accept the next aminoacyl-tRNA. Elongation is the repetitive cycle that builds the polypeptide chain one amino acid at a time, and it proceeds through three distinct steps: codon-directed binding, peptide bond formation, and translocation.

In the first step, an aminoacyl-tRNA does not simply float into the A site on its own. Instead, the elongation factor EF-Tu (in prokaryotes) or eEF1A (in eukaryotes) delivers it in a complex with GTP. Think of EF-Tu as an escort with a security clearance — it brings the charged tRNA to the ribosome and holds it in position while the ribosome checks whether the anticodon matches the codon in the A site. If the match is correct, the geometry of the codon-anticodon interaction triggers a conformational change in the ribosome that stimulates GTP hydrolysis on EF-Tu. This is the proofreading step: the energy of GTP hydrolysis is used not to form the peptide bond itself, but to introduce a kinetic delay that gives incorrectly matched tRNAs time to dissociate before the irreversible step. Only after GTP hydrolysis and EF-Tu release is the aminoacyl-tRNA fully accommodated into the A site.

Once the correct aminoacyl-tRNA is in the A site, peptidyl transferase — an activity of the ribosomal RNA itself (making the ribosome a ribozyme) — catalyzes formation of a peptide bond between the amino acid on the A-site tRNA and the growing polypeptide chain attached to the P-site tRNA. The polypeptide is transferred from the P-site tRNA to the A-site tRNA, leaving a deacylated (empty) tRNA in the P site. At this point, the ribosome is in a hybrid state — the tRNAs have shifted relative to the large subunit but not yet relative to the small subunit.

The final step of each cycle is translocation, driven by the elongation factor EF-G (prokaryotes) or eEF2 (eukaryotes). EF-G binds the ribosome with GTP and, upon hydrolysis, physically moves the ribosome one codon down the mRNA. The deacylated tRNA shifts from the P site to the E site (exit site) and is released, the peptidyl-tRNA moves from A to P, and a new codon is exposed in the empty A site. The entire cycle then repeats — at a remarkable rate of about 15–20 amino acids per second in bacteria. Each elongation factor participates transiently: EF-Tu and EF-G bind, do their work, and dissociate within each cycle. EF-Tu is recharged by the exchange factor EF-Ts, which swaps GDP for GTP, readying EF-Tu for another round of tRNA delivery.

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 → mRNA Translation Start Sites and Initiation → Ribosomal Initiation Factors and Initiator tRNA → Translation Elongation and Elongation Factors

Longest path: 215 steps · 1098 total prerequisite topics

Prerequisites (2)

Ribosomal Initiation Factors and Initiator tRNAhard Translation Elongation and Termination: Peptide Bond Formationsoft

Leads To (1)

Translation Termination and Release Factorshard