What is Dr. Zubair Khalid's research focus?

Dr. Zubair Khalid specializes in molecular virology, mRNA vaccine development, and computational biology, with a focus on avian pathogens like IBDV and Avian Reovirus.

Where is Dr. Zubair Khalid currently working?

Dr. Zubair Khalid is a Postdoctoral Research Associate at the University of Maryland (UMD), specifically within the Department of Animal and Avian Sciences.

tRNA Anticodon: Structure, Function, and Role in Translation

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-11

Key Takeaways

The tRNA anticodon is a three-nucleotide sequence that forms antiparallel base pairs with a complementary codon on mRNA within the ribosome's decoding center, acting as the crucial molecular bridge for translating genetic information into protein sequences.
Codon-anticodon recognition is governed by standard Watson-Crick base pairing for the first two codon positions, while the third codon position exhibits "wobble" pairing, allowing a single tRNA to recognize multiple codons and explaining the degeneracy of the genetic code.
Modified nucleotides, particularly inosine (I) at the anticodon's wobble position (34) and modified purines at position 37, are critical for fine-tuning codon recognition specificity, expanding decoding capacity, and preventing translational frameshifts.
The ribosome's decoding center, involving conserved rRNA residues, monitors the geometry of the codon–anticodon helix, and kinetic proofreading mechanisms, involving elongation factor Tu (EF-Tu) and GTP hydrolysis, ensure high translational fidelity by rejecting near-cognate tRNAs.
Advanced techniques like tRNA sequencing (tRNA-seq) and cryo-electron microscopy (cryo-EM) are indispensable for characterizing tRNA anticodon sequences, their abundance, and their precise structural interactions with the ribosome during translation elongation.

Introduction to the tRNA Anticodon

The tRNA anticodon is a three-nucleotide sequence located on transfer RNA (tRNA) that base-pairs with a complementary three-nucleotide codon on messenger RNA (mRNA) during protein synthesis. This interaction is the molecular event that decodes the genetic information stored in mRNA into the amino acid sequence of a protein. Without the anticodon, the ribosome would have no way to match each codon with its corresponding amino acid, and the entire process of translation would collapse into nonsense.

The anticodon is the physical bridge between the language of nucleic acids (nucleotide sequence) and the language of proteins (amino acid sequence). Each tRNA molecule carries a specific amino acid at one end and displays a specific anticodon at the other. When the anticodon pairs correctly with an mRNA codon in the ribosome, the attached amino acid is added to the growing polypeptide chain. This codon–anticodon recognition is the basis of the genetic code's translation into functional proteins.

What is an anticodon?

An anticodon is a contiguous sequence of three nucleotides on a tRNA molecule that is complementary to a codon on mRNA. The anticodon is positioned in a single-stranded loop of the tRNA structure, where it is accessible for base pairing with the mRNA codon. The pairing occurs in an antiparallel orientation, meaning the 5′ end of the anticodon pairs with the 3′ end of the codon, and vice versa.

For example, if an mRNA codon is 5′-AUG-3′, the corresponding tRNA anticodon is 3′-UAC-5′. Note that the anticodon is written in the 3′ to 5′ direction to emphasize its antiparallel alignment with the codon. This simple complementarity rule—A pairs with U, G pairs with C—governs the initial recognition, but as we will see, the rules are relaxed at the third position of the codon through a mechanism called wobble.

Anticodon vs. codon

The codon and anticodon are often confused because they are both three-nucleotide sequences involved in the same process. The distinction is straightforward:

Codon: A three-nucleotide sequence on mRNA that specifies a particular amino acid or a stop signal. Codons are read in the 5′ to 3′ direction by the ribosome.
Anticodon: A three-nucleotide sequence on tRNA that is complementary to the codon. The anticodon is read in the 3′ to 5′ direction when aligned with the codon.

The codon is the "message" and the anticodon is the "reader." The codon is found on mRNA, the anticodon on tRNA. The codon determines which amino acid is added; the anticodon ensures the correct tRNA—and therefore the correct amino acid—is selected. For a more detailed comparison, see the Codon Anticodon resource.

Structure of tRNA and the Anticodon Loop

Transfer RNA is a small RNA molecule, typically 73 to 93 nucleotides in length, that adopts a highly conserved three-dimensional structure. The primary sequence folds into a cloverleaf secondary structure characterized by four base-paired stems and three loops. The tertiary structure, however, is an L-shaped molecule that positions the anticodon at one end and the amino acid attachment site at the other, separated by approximately 76 Å.

The cloverleaf structure consists of:

Acceptor stem: The 5′ and 3′ ends of the tRNA base-pair to form a stem. The 3′ end carries the conserved CCA sequence, to which the amino acid is attached.
D-arm (DHU arm): Contains the dihydrouridine loop, which contributes to tertiary folding.
Anticodon arm: Contains the anticodon loop and the anticodon stem.
T-arm (TΨC arm): Contains the ribothymidine-pseudouridine-cytidine loop, which interacts with the ribosome.
Variable loop: A region of variable length between the anticodon arm and the T-arm.

The L-shaped tertiary structure is formed by extensive base stacking and hydrogen bonding between the D-arm and T-arm, creating a rigid scaffold. The anticodon loop is located at one end of the L, while the amino acid attachment site (the 3′ CCA end) is at the other. This spatial separation is functionally critical: the anticodon must interact with mRNA in the ribosome's decoding center, while the amino acid must be positioned in the peptidyl transferase center for peptide bond formation.

The anticodon loop

The anticodon loop is typically seven nucleotides long, with the anticodon triplet occupying positions 34, 35, and 36 of the tRNA sequence. These positions are numbered from the 5′ end of the mature tRNA. The anticodon triplet is flanked by two purine bases on the 5′ side (positions 32 and 33) and a purine at position 37 on the 3′ side. These flanking nucleotides are not part of the anticodon itself but play critical roles in stabilizing the loop structure and modulating codon recognition.

The loop is structured so that the anticodon bases are presented in a stacked, single-stranded conformation that is optimally positioned for base pairing with the mRNA codon. The bases at positions 32 and 38 form a non-Watson-Crick interaction that caps the loop and helps orient the anticodon. The nucleotide at position 37, typically a modified purine, stacks on top of the anticodon and prevents frameshifting by stabilizing the codon–anticodon interaction.

Modified nucleotides in the anticodon

Transfer RNAs contain a remarkable number of modified nucleotides, with over 100 different modifications identified across all organisms. The anticodon loop is a hotspot for these modifications, particularly at position 34 (the wobble position) and position 37 (the base immediately 3′ to the anticodon). These modifications are not decorative; they are functionally essential for accurate and efficient translation.

Common modifications at position 34 include:

Inosine (I): Formed by deamination of adenine. Inosine can pair with U, C, or A, greatly expanding the decoding capacity of a single tRNA.
5-methylaminomethyl-2-thiouridine (mnm⁵s²U): Found in tRNAs reading codons ending in A or G. The thiolation restricts pairing to A, preventing misreading of codons ending in U or C.
5-oxyacetic acid uridine (cmo⁵U): Found in tRNAs reading codons ending in U or C, where it permits wobble pairing with both.

Modifications at position 37 include:

N⁶-isopentenyladenosine (i⁶A): Found in tRNAs that read codons starting with U. It prevents frameshifting by stabilizing the codon–anticodon interaction.
1-methylguanosine (m¹G): Found in tRNAs reading codons starting with C. It prevents mispairing and maintains the reading frame.

These modifications fine-tune the thermodynamics of codon–anticodon pairing, ensuring that the correct tRNA is selected while incorrect tRNAs are rejected. For a deeper look at tRNA architecture, see tRNA Structure.

Codon-Anticodon Base Pairing

The interaction between a codon and an anticodon is a specific, non-covalent base-pairing event that occurs within the ribosome's decoding center. This interaction must be both specific enough to ensure accurate translation and rapid enough to allow protein synthesis to proceed at rates of 5 to 20 amino acids per second in bacterial cells.

Antiparallel alignment

The codon and anticodon align in an antiparallel fashion, meaning the 5′ end of one pairs with the 3′ end of the other. The mRNA codon is read in the 5′ to 3′ direction, and the anticodon is aligned in the 3′ to 5′ direction. This means:

The first base of the codon (5′ position) pairs with the third base of the anticodon (3′ position).
The second base of the codon pairs with the second base of the anticodon.
The third base of the codon (3′ position) pairs with the first base of the anticodon (5′ position).

For example, the codon 5′-AUG-3′ pairs with the anticodon 3′-UAC-5′. The A at the 5′ end of the codon pairs with the U at the 3′ end of the anticodon; the U in the middle pairs with the A in the middle; and the G at the 3′ end of the codon pairs with the C at the 5′ end of the anticodon.

This antiparallel arrangement is dictated by the chemical polarity of the nucleic acid backbones. The ribosome positions the mRNA and tRNA such that their 5′→3′ orientations are opposite, allowing the bases to form standard Watson-Crick hydrogen bonds.

Wobble hypothesis

The genetic code is degenerate, meaning that most amino acids are specified by more than one codon. For example, leucine is encoded by six codons (UUA, UUG, CUU, CUC, CUA, CUG), and serine is encoded by six codons (UCU, UCC, UCA, UCG, AGU, AGC). If each codon required a unique tRNA with a perfectly complementary anticodon, a cell would need at least 61 different tRNAs (one for each sense codon). In reality, most cells have 30 to 50 tRNA species, and the discrepancy is explained by the wobble hypothesis.

Proposed by Francis Crick in 1966, the wobble hypothesis states that the base at the 5′ position of the anticodon (position 34) can pair with more than one base at the 3′ position of the codon (the third codon position). This non-standard pairing is called "wobble" because the geometry of the base pair is slightly distorted compared to standard Watson-Crick pairing.

The wobble rules are:

Anticodon base (position 34)	Can pair with codon base (position 3)
G	U or C
C	G
A	U (rare, mostly in mitochondria)
U	A or G
I (inosine)	U, C, or A

The most important wobble base is inosine, which can pair with U, C, or A. This single modification allows one tRNA to read up to three different codons. For example, a tRNA with the anticodon 3′-CCI-5′ can read the codons 5′-GGU-3′, 5′-GGC-3′, and 5′-GGA-3′, all of which encode glycine.

The wobble position is always the first base of the anticodon (position 34) and the third base of the codon. The first two bases of the codon must pair with strict Watson-Crick geometry, as these interactions are monitored by the ribosome's decoding center with high precision. The wobble position, by contrast, is subject to more relaxed constraints, allowing a single tRNA to decode multiple codons.

Wobble Hypothesis and Degeneracy

The wobble hypothesis explains how the degeneracy of the genetic code is managed at the molecular level. Degeneracy means that multiple codons can specify the same amino acid, and wobble allows a limited set of tRNAs to cover all possible codons without requiring a one-to-one correspondence.

Wobble rules

The complete set of wobble rules, as refined by subsequent research, is as follows:

Standard Watson-Crick pairing is required at the first two codon positions.
At the third codon position, the following non-standard pairs are permitted:
G in the anticodon can pair with U in the codon.
U in the anticodon can pair with G in the codon.
I (inosine) in the anticodon can pair with U, C, or A in the codon.
Pairing with C or A in the anticodon is generally restricted to G and U, respectively, with exceptions in specific contexts.

These rules mean that a tRNA with the anticodon 3′-GAA-5′ can read both 5′-CUU-3′ and 5′-CUC-3′ (both encoding leucine), while a tRNA with the anticodon 3′-UUC-5′ can read both 5′-GAA-3′ and 5′-GAG-3′ (both encoding glutamic acid).

The wobble rules are not universal in their details; different organisms and different cellular compartments (e.g., mitochondria) have evolved variations. For instance, mitochondrial tRNAs often have more relaxed wobble, allowing a single tRNA to read an entire codon family. In contrast, some bacterial tRNAs have restricted wobble to maintain translational accuracy under specific growth conditions.

Inosine and modified bases

Inosine is the most versatile wobble base. It is formed by the enzymatic deamination of adenine at position 34, catalyzed by the enzyme tRNA adenosine deaminase (TadA in bacteria, ADAT in eukaryotes). Inosine can form stable base pairs with U, C, and A, but not with G. This allows a single tRNA containing inosine at the wobble position to decode three codons that differ only in their third base.

For example, the tRNA for alanine has the anticodon 3′-CGI-5′. This tRNA can read the codons 5′-GCU-3′, 5′-GCC-3′, and 5′-GCA-3′, all of which encode alanine. The fourth alanine codon, 5′-GCG-3′, is read by a separate tRNA with the anticodon 3′-CGC-5′.

Modified bases at position 34 can also restrict or expand wobble capacity. For example:

2-thiouridine (s²U) at position 34 restricts pairing to A, preventing misreading of codons ending in G. This is important for tRNAs that must distinguish between codons ending in A and G, such as the glutamine codons CAA and CAG.
5-methyl-2-thiouridine (m⁵s²U) similarly restricts pairing to A, ensuring accurate reading of codons ending in A.
5-oxyacetic acid uridine (cmo⁵U) allows pairing with both U and C, expanding the decoding capacity of tRNAs that read two-codon sets.

These modifications are introduced by specific enzymes, such as the sulfurtransferase MnmA in bacteria, which adds the thio group to uridine at position 34. Defects in these modification enzymes lead to severe growth defects and translational errors, underscoring their functional importance.

Role of Anticodon in Translation Elongation

The anticodon is not merely a passive recognition element; it is an active participant in the translation elongation cycle, interacting with the ribosome's decoding center and contributing to the accuracy of protein synthesis. The elongation cycle involves three main steps: aminoacyl-tRNA delivery to the A-site, peptide bond formation, and translocation.

A-site binding

During elongation, the ribosome has three tRNA binding sites: the A-site (aminoacyl), the P-site (peptidyl), and the E-site (exit). The mRNA codon in the A-site is the next codon to be decoded. An aminoacyl-tRNA, complexed with elongation factor Tu (EF-Tu in bacteria, eEF1A in eukaryotes) and GTP, is delivered to the A-site.

The anticodon of the incoming tRNA must base-pair with the A-site codon. This interaction is monitored by the ribosome's decoding center, which comprises conserved 16S rRNA residues in the small subunit (in bacteria, bases A1492, A1493, and G530). These residues form hydrogen bonds with the minor groove of the codon–anticodon helix, checking that the geometry of the first two base pairs is correct.

The decoding center does not directly check the third base pair, which is why wobble is permitted at this position. However, the overall stability of the codon–anticodon interaction, including the wobble pair, contributes to the discrimination between cognate (correct) and near-cognate (incorrect) tRNAs.

If the anticodon matches the codon, the ribosome undergoes a conformational change that triggers GTP hydrolysis by EF-Tu, releasing the tRNA into the A-site and allowing peptide bond formation. If the anticodon does not match, the tRNA dissociates, and the incorrect amino acid is not incorporated.

Kinetic proofreading

The accuracy of translation is remarkably high, with an error rate of approximately 1 in 1,000 to 1 in 10,000 amino acids incorporated. This accuracy is achieved through a two-step selection process known as kinetic proofreading.

The first step occurs during initial codon recognition, before GTP hydrolysis. The binding of a near-cognate tRNA (one with a single mismatch) is less stable than that of a cognate tRNA, so it dissociates more rapidly. The second step occurs after GTP hydrolysis but before peptide bond formation. The ribosome undergoes a second round of selection, and near-cognate tRNAs are rejected at this stage as well.

The kinetic proofreading mechanism exploits the difference in activation energy between cognate and near-cognate codon–anticodon interactions. A cognate interaction induces a conformational change in the ribosome (domain closure of the small subunit) that accelerates GTP hydrolysis by EF-Tu. A near-cognate interaction fails to induce this conformational change efficiently, so GTP hydrolysis is slow, and the tRNA is more likely to dissociate before committing to peptide bond formation.

The rate constants for these steps have been measured in vitro: cognate tRNAs are bound and GTP hydrolyzed within milliseconds, while near-cognate tRNAs are rejected with rate constants that are 100- to 1,000-fold slower. This kinetic discrimination, combined with the structural monitoring by the decoding center, ensures that the correct amino acid is added with high fidelity.

Methods to Study tRNA Anticodons

Understanding the structure, function, and dynamics of tRNA anticodons requires a combination of biochemical, structural, and computational approaches. Each method provides complementary information, from the sequence of the anticodon to its three-dimensional conformation within the ribosome.

tRNA-seq

tRNA sequencing (tRNA-seq) is a high-throughput method to determine the sequences and abundances of all tRNAs in a cell. Because tRNAs are heavily modified and highly structured, standard RNA-seq protocols are often inadequate. Specialized tRNA-seq methods use enzymes such as demethylases to remove modifications that block reverse transcription, or use specialized reverse transcriptases that can read through modified bases.

tRNA-seq can identify the anticodon sequence of every tRNA in an organism, as well as the relative abundance of each tRNA under different conditions. For example, tRNA-seq has revealed that tRNA abundance changes in response to amino acid starvation, with specific tRNAs being upregulated to match the codon usage of stress-response genes. This technique is essential for understanding how the tRNA pool is regulated to meet the demands of protein synthesis.

The anticodon sequence is directly read from the tRNA-seq data, allowing researchers to predict which codons each tRNA can decode based on wobble rules. Combining tRNA-seq with ribosome profiling (which measures the positions of ribosomes on mRNA) can reveal how tRNA availability affects translation efficiency and accuracy.

Cryo-electron microscopy

Cryo-electron microscopy (cryo-EM) has revolutionized the study of tRNA–ribosome interactions. By flash-freezing ribosomes in various states of the translation cycle and imaging them with an electron microscope, researchers can obtain near-atomic-resolution structures of the ribosome with tRNAs bound in the A, P, and E sites.

Cryo-EM structures have revealed the precise geometry of codon–anticodon base pairing in the decoding center. For example, structures of the bacterial ribosome with cognate and near-cognate tRNAs bound have shown how the decoding center monitors the minor groove of the codon–anticodon helix. These structures have also captured the conformational changes that occur during tRNA selection, including the domain closure of the small subunit that precedes GTP hydrolysis.

More recently, cryo-EM has been used to visualize the effects of modified nucleotides in the anticodon loop. Structures of tRNAs with inosine at position 34 have shown how this modified base adopts a conformation that allows it to pair with U, C, or A without disrupting the overall geometry of the codon–anticodon interaction.

Molecular dynamics simulations

Molecular dynamics (MD) simulations complement experimental methods by providing atomistic details of anticodon dynamics. In an MD simulation, the positions of all atoms in a system (e.g., a tRNA bound to the ribosome) are propagated forward in time using Newton's equations of motion. These simulations can reveal the conformational flexibility of the anticodon loop, the stability of wobble base pairs, and the pathways by which tRNAs are selected or rejected.

MD simulations have been used to study the thermodynamics of codon–anticodon pairing, showing that wobble pairs are less stable than Watson-Crick pairs but are stabilized by the surrounding ribosome environment. Simulations have also explored how modified nucleotides at positions 34 and 37 affect the dynamics of the anticodon loop, providing a molecular explanation for their functional roles.

For example, simulations of the anticodon loop with a modified base at position 37 have shown that the modification stacks on the adjacent base, rigidifying the loop and preventing frameshifting. These computational insights are valuable for interpreting experimental data and for designing mutations that alter anticodon function.

Common Misconceptions and Pitfalls

Students frequently encounter several conceptual difficulties when learning about tRNA anticodons. Understanding these pitfalls is essential for mastering the material and avoiding errors on exams.

Anticodon vs. codon confusion

The most common error is confusing the anticodon with the codon. Remember:

The codon is on mRNA and is read 5′ to 3′.
The anticodon is on tRNA and is written 3′ to 5′ when aligned with the codon.

When asked to find the anticodon for a given codon, first write the codon in the 5′ to 3′ direction, then write the complementary sequence in the 3′ to 5′ direction. For example, for the codon 5′-AUG-3′, the anticodon is 3′-UAC-5′. A common mistake is to write 5′-UAC-3′, which is the reverse complement and is incorrect.

Forgetting antiparallel orientation

Another frequent error is forgetting that codon–anticodon pairing is antiparallel. This means that the first base of the codon pairs with the third base of the anticodon, not the first. When drawing the pairing, always align the 5′ end of the codon with the 3′ end of the anticodon.

A useful trick is to write the codon in the 5′ to 3′ direction and the anticodon directly below it in the 3′ to 5′ direction, then pair the bases vertically. This makes the antiparallel alignment visually obvious.

Wobble misconceptions

Students often misunderstand the wobble hypothesis in several ways:

Wobble applies only to the third codon position: Correct. The first two positions must form Watson-Crick pairs. Wobble never occurs at the first or second position of the codon.
Wobble means any non-standard pairing is allowed: Incorrect. Wobble follows specific rules. For example, G can pair with U, but not with A or C. Inosine can pair with U, C, or A, but not with G.
Wobble reduces accuracy: Wobble is a controlled relaxation of specificity that is monitored by the ribosome. It does not increase the error rate because the first two codon positions provide most of the specificity, and the ribosome's proofreading mechanisms reject incorrect tRNAs.

Misreading the genetic code

Students sometimes assume that the anticodon directly specifies the amino acid. In reality, the amino acid is attached to the tRNA by aminoacyl-tRNA synthetases, which recognize the tRNA's overall structure, including the anticodon and the acceptor stem. The anticodon is one of the identity elements that the synthetase uses to ensure the correct amino acid is attached. For a given tRNA, the anticodon and the amino acid are matched, but the anticodon itself does not "code" for the amino acid in a chemical sense.

Summary and Key Takeaways

The tRNA anticodon is a small but functionally critical element of the translation machinery. It is the molecular interface between the genetic code and protein synthesis, ensuring that each codon is matched with the correct amino acid.

Key points

The anticodon is a three-nucleotide sequence on tRNA that base-pairs with the mRNA codon in an antiparallel orientation.
The anticodon is located in the anticodon loop at one end of the L-shaped tRNA structure, while the amino acid is attached at the opposite end.
The first two bases of the codon form Watson-Crick pairs with the anticodon, while the third base can form wobble pairs.
The wobble hypothesis explains how a single tRNA can decode multiple codons, contributing to the degeneracy of the genetic code.
Modified nucleotides at positions 34 and 37 of the tRNA modulate wobble pairing and prevent frameshifting.
The ribosome's decoding center monitors codon–anticodon geometry, and kinetic proofreading ensures high translational accuracy.
Experimental methods such as tRNA-seq, cryo-EM, and molecular dynamics simulations provide detailed insights into anticodon structure and function.

Quick revision checklist

Can you define the anticodon and distinguish it from the codon?
Can you write the anticodon for any given codon, maintaining antiparallel orientation?
Can you state the wobble rules and give an example of a tRNA that reads multiple codons?
Can you explain how modified nucleotides in the anticodon loop affect decoding?
Can you describe the role of the anticodon in A-site binding and kinetic proofreading?
Can you name two experimental methods used to study anticodons and what they reveal?

Frequently Asked Questions

What is a tRNA anticodon?

A tRNA anticodon is a sequence of three nucleotides on a transfer RNA molecule that is complementary to a codon on messenger RNA. It base-pairs with the mRNA codon during translation, ensuring that the correct amino acid is added to the growing polypeptide chain. The anticodon is located in the anticodon loop at one end of the tRNA, while the amino acid is attached at the opposite end.

Is the anticodon on tRNA or mRNA?

The anticodon is on tRNA. The codon is on mRNA. The anticodon base-pairs with the codon in an antiparallel orientation, with the 5′ end of the codon pairing with the 3′ end of the anticodon. This interaction occurs in the ribosome's A-site during translation elongation.

How do you find the anticodon for a given codon?

To find the anticodon for a given codon, write the codon in the 5′ to 3′ direction, then write the complementary sequence in the 3′ to 5′ direction. For example, for the codon 5′-AUG-3′, the complementary bases are UAC, and the anticodon is written as 3′-UAC-5′. Remember that the anticodon is antiparallel to the codon, so the first base of the codon pairs with the third base of the anticodon.

What is an example of a tRNA anticodon?

An example is the tRNA for methionine, which has the anticodon 3′-UAC-5′. This anticodon pairs with the codon 5′-AUG-3′ on mRNA, which encodes methionine. Another example is the tRNA for glycine with the anticodon 3′-CCI-5′, which can read the codons 5′-GGU-3′, 5′-GGC-3′, and 5′-GGA-3′ due to inosine wobble.

What is the difference between a codon and an anticodon?

A codon is a three-nucleotide sequence on mRNA that specifies an amino acid or a stop signal. An anticodon is a three-nucleotide sequence on tRNA that is complementary to the codon. The codon is read in the 5′ to 3′ direction, while the anticodon is aligned in the 3′ to 5′ direction. The codon determines which amino acid is added; the anticodon ensures the correct tRNA is selected.

What is wobble base pairing?

Wobble base pairing is a non-standard base pair that occurs at the third position of the codon (the 5′ position of the anticodon). It allows a single tRNA to recognize multiple codons that differ only in their third base. For example, the wobble base inosine can pair with U, C, or A, and G can pair with U. Wobble pairing is permitted only at the third codon position; the first two positions must form standard Watson-Crick pairs.

Why is the anticodon important in translation?

The anticodon is essential for translation because it ensures that the correct amino acid is added to the growing polypeptide chain. By base-pairing with the mRNA codon in the ribosome's A-site, the anticodon determines which tRNA is selected and therefore which amino acid is incorporated. The accuracy of this selection is critical for producing functional proteins, and errors in anticodon–codon pairing can lead to misfolded or nonfunctional proteins.