Codon Chart – Codon Table, mRNA Codon Chart, Amino Acids & RNA Wheel Explained

A codon chart acts like life’s universal genetic dictionary, translating sequences of three DNA or RNA letters (called codons) into the 20 amino acids that build proteins. It’s essential because nearly all living things — from bacteria to humans — use this same code, allowing scientists to engineer life-saving breakthroughs like bacteria-produced insulin or mRNA vaccines. The chart’s clever design includes built-in error protection: many amino acids have multiple codons, so small genetic typos often don’t disrupt protein function.

This system was deciphered in the 1960s by biochemists Marshall Nirenberg and Har Gobind Khorana, who used synthetic RNA to crack the first codons (like UUU for phenylalanine). Their Nobel Prize-winning work created the chart still used today in genetics labs, medical research, and biotechnology — proving how understanding nature’s code transforms human health.

What is a Codon Chart?

• A codon chart (aka codon table) is a visual reference that maps all 64 possible three‑nucleotide codons (in mRNA or DNA) to their encoded amino acids or stop/start signals
• It shows the first codon base on one axis (usually left), the second base on another (top), and the third base on a third axis or within each cell.
• Tables commonly use a square format but can also appear as circular “codon wheels”, both working the same way by sequential base selection.
• Charts highlight key codons such as AUG (start codon, methionine) and the three stop codons UAA, UAG, UGA (ochre, amber, opal)
• Redundancy (degeneracy) is visible, for example several codons differing only at third base encode same amino acid (like GCU, GCC, GCA, GCG → alanine).
• Charts aid translation of mRNA sequences into amino acid chains by stepping through codons in reading frame from 5′ to 3′ end.
• Specialized versions exist for mitochondrial or other variant genetic codes to account for differences in codon usage

20 standard amino acids with their three-letter and one-letter abbreviations:

• Alanine (Ala, A)
• Arginine (Arg, R)
• Asparagine (Asn, N)
• Aspartic acid (Asp, D)
• Cysteine (Cys, C)
• Glutamic acid (Glu, E)
• Glutamine (Gln, Q)
• Glycine (Gly, G)
• Histidine (His, H)
• Isoleucine (Ile, I)
• Leucine (Leu, L)
• Lysine (Lys, K)
• Methionine (Met, M)
• Phenylalanine (Phe, F)
• Proline (Pro, P)
• Serine (Ser, S)
• Threonine (Thr, T)
• Tryptophan (Trp, W)
• Tyrosine (Tyr, Y)
• Valine (Val, V)

Codon Chart

How do you read a codon table?

1. Find your mRNA codon – pick three bases in 5′ to 3′ order
2. Look at the first base (left side of chart) to select the row corresponding to that nucleotide.
3. Move to the second base (top of chart) and identify the column that matches
4. Within the grid cell, check the subdivisions to locate the third base (often listed inside or at right side of each cell)
5. The amino acid (or start/stop signal) shown in that cell is what your codon encodes.
6. For AUG you’ll note both methionine and “start” label.
7. For UAA, UAG, UGA you’ll see they map to stop signals.
8. Continue reading successive codons in the same reading frame until you hit a stop codon.
9. If you want to translate a full mRNA sequence, segment it into triplets, then apply steps 1‑7 to each until the stop codon ends translation.
10. Use circular codon wheels the same way, but rotate through first, second, third bases in concentric rings instead of rows/columns

Here is an example – How do you read a codon table?

To read the codon chart, find the amino acid that forms a three-nucleotide sequence, or codon, in mRNA. The chart translates mRNA to its equivalent amino acid. Here’s how it works:

Here’s a clear step‑by‑step guide to reading the codon chart you provided:

• Start with an mRNA codon of 3 bases in 5′→3′ direction, e.g. “AGU”
• Find the first base on the left-hand axis (rows labeled U, C, A, G); for AGU you go to row A
• Then find the second base on the top axis (columns U, C, A, G); here it’s G, so locate intersection where row A meets column G
• Inside that grid box you’ll see 4 small entries, one for each possible third base; these are labeled U, C, A, G vertically or listed together
• Find your third base, here it’s U, so pick the entry “AGU”
• The entry tells you which amino acid or signal, e.g. “Ser” (serine)
• Note special cases:
  • “AUG” is marked green as Met (start)
  • “UAA, UAG, UGA” are red and labeled STOP
• Repeat for each consecutive triplet until a stop codon appears terminating translation
• If using a codon wheel, same logic applies: choose rings for first, second, third base from center

so summary: choose first, then second, then third base, then read inside cell to get amino acid or stop/start.

What are Start Codons?

• Start codon is a triplet in mRNA that signals ribosome to begin translation
• Most common start codon is AUG
• It codes for methionine in eukaryotes, formyl-methionine in prokaryotes
• Sets correct reading frame for decoding rest of the mRNA
• GUG and UUG sometimes act as start codons in bacteria
• In eukaryotes, AUG often surrounded by kozak sequence to help recognition
• In bacteria, shine dalgarno sequence helps ribosome align with start codon
• Even if GUG or UUG used, they still insert methionine during initation
• Only one start codon used per mRNA during translation
• Translation always begins at first recognized start codon from 5′ to 3′ end

How to Read a Codon Wheel?

1. First locate the first base of your mRNA codon at the center of the wheel (e.g., for codon “ACU,” start with A in the inner circle).
2. Next move to the middle ring for the second base, following outward from center (e.g., from A go to C)
3. Then proceed to the outer ring to select the third base (e.g., from A → C ring go to U).
4. The sector where the third-base ring lands shows the amino acid name or stop signal (e.g., ACU → Thr).
5. Check for markers: start codon often highlighted (arrow icon), and stop codons have special stop labels.
6. Read codons from 5′ end to 3′ end of mRNA, each triplet using the wheel to map to amino acids sequentially.
7. Continue until a stop codon appears, then release factors terminate translation

summary: inner→middle→outer rings give first→second→third base, outermost segment names amino acid or stop. Wheel mirrors square chart logic but in circular form, easier for quick lookup during translation

What are Stop Codons?

• Stop codons are three‑nucleotide sequences in mRNA that signal the ribosome to terminate translation
• The three standard stop codons are UAA (ochre), UAG (amber), and UGA (opal or umber).
• Stop codons don’t code for amino acids; instead they attract release factors that bind in the ribosomal A-site and trigger peptide release and ribosome disassembly.
• In bacteria, release factors RF1 recognizes UAA and UAG, RF2 recognizes UAA and UGA, and RF3 functions as a GTPase to recycle RF1/RF2.
• In eukaryotes, a single release factor eRF1 recognizes all three stop codons, aided by eRF3‑GTP complex to perform hydrolysis.
• Stop codons effectively define the end of the open reading frame ensuring proteins are made at correct lengths.
• Occasionally translational readthrough happens if near-cognate tRNAs suppress stop codon, but it’s rare and context dependent.
• Variations exist in mitochondrial or some ciliate codes where stop codons are reassigned to encode amino acids.

What is Codon Translation?

Codon translation is the process where ribosomes read mRNA codons (three‑base units) to assemble amino acids into proteins. it begins after transcription when mRNA moves to ribosome in cytoplasm (or ER in eukaryotes).

Ribosome loads at start codon (usually AUG) and reads codons 5′→3′ to maintain reading frame. Each codon is matched by a tRNA anticodon, bringing a specific amino acid.

Peptide bonds form between amino acids, elongating the polypeptide chain. This continues until a stop codon (UAA, UAG, UGA) enters the ribosome’s A‑site.

Release factors recognize stop codon and promote release of polypeptide, leading to ribosome dissociation. Result is a polypeptide that folds into functional protein, ready for cell tasks.

Accuracy depends on correct start site, codon‑anticodon pairing, and absence of frame shifts

What is dna codon chart?

• dna codon chart shows 64 triplets on sense strand, with thymine (T) replacing uracil (U) in rna version
• chart is often circular: inner ring = first base, middle = second, outer = third.
• to read it: pick first base (e.g., T) at center, then second base (e.g., G) in next ring, then third base (e.g., A) in outermost ring → that codon maps to an amino acid (e.g., GTA → Valine).
• square table version: row = first base, column = second, within cell subdivided by third → gives amino acid or stop/start.
• stop codons in dna are TAG, TGA, TAA, highlighted as “Stop” signals.
• start codon in dna is ATG, codes for methionine; rna equivalent is AUG
• chart reveals degeneracy: third‑base variation often yields same amino acid (such as GCT, GCC, GCA, GCG → alanine).
• chart supports dna→mrna translation flow: dna codons transcribed to rna, then read by ribosome

What is mRNA codon chart?

• An mRNA codon chart is a reference table listing all 64 three‑base codons made from U, C, A, G and their corresponding amino acids or stop signals
• Usually formatted as a square grid or concentric wheel:
  • square version has rows for first base (U, C, A, G), columns for second base, and subdivisions inside each cell for third base
  • wheel version uses concentric circles: center = first base, middle = second, outer = third
• Reading step‑by‑step in square chart:
  1. find your codon’s first base on left axis
  2. find second base on top axis
  3. go to intersecting cell and look for the entry matching third base
  4. read the amino acid name or see “stop”/“start” label.
• example: codon ACU → row A, column C, third base U → maps to Thr (threonine) and shows degeneracy since ACC, ACA, ACG also code for Thr.
• chart highlights key codons: AUG = start/methionine (in green), UAA/UAG/UGA = stop codons (in red).
• Wheel usage follows same logic: start at center with first base, move outward for second and then third base to find amino acid name in outer ring.
• Codon chart reflects genetic code degeneracy where different codons yield same amino acid, ensuring robustness.
• chart is universal across most organisms with rare variants (mitochondrial codes etc.)

This chart is essential for translating mRNA sequences: guide ribosomes from start to stop codon ensuring correct amino acid chain formation.

Amino acid Codon Related Online Tools

• Amino Acid to Codon Mapper
• Codon Wheel Explorer
• Codon to Amino Acid Translator
• Interactive Codon Chart Tool