John Hay
John Hay Biomedical
Student Hub · Go Hornets 🐝
My ClassGlossaryAboutFeedback
Principles of Biomedical Technology (Principles of Biomedical Science)
Unit 2: Unit 2.2 Decoding a DiagnosisPBS 2.2Biotechnology Research and Experiments

Read A Codon Chart

Look up mRNA codons on a chart to name the amino acid, the start codon, and the stop codons.

Builds on (2 levels back)inferred · high confidence
  • A codon is three bases: You must read the mRNA in groups of three to use the chart.
  • Reading frame: Where you start reading sets the codons, so the frame must stay consistent.

Prerequisites are inferred: pending teacher review.

Re-learn the skill with worked practice and clear examples.

Practice plain lookups: read a codon, find its row on the chart, and write the amino acid: and recognize a stop codon when you hit one.

Step 1: Match the codon to a row
Take the three-base codon and find the same three letters in the chart's left column.
Step 2: Read across
Write the amino acid listed across from it. UUU = Phenylalanine, UGG = Tryptophan, GCA = Alanine.
Step 3: Spot a stop
If the row says STOP (UAA, UAG, or UGA), the protein ends there: no amino acid is added.
Practice

Using the codon chart, which amino acid does the mRNA codon UUU code for?

Approved
mRNA codonMeaning
AUGMethionine (Met) - START
UUUPhenylalanine (Phe)
UGGTryptophan (Trp)
GCAAlanine (Ala)
UAASTOP
UAGSTOP
UGASTOP
A short codon chart linking mRNA codons to amino acids, the start codon, and stop codons.
  1. A.Phenylalanine (Phe)
  2. B.Methionine (Met)
  3. C.Tryptophan (Trp)
  4. D.Stop
Show the worked solution ▾

Answer: A. Phenylalanine (Phe)

  1. Step 1: Find UUU: Locate UUU in the chart's codon column.
  2. Step 2: Read its amino acid: Across from UUU the chart lists Phenylalanine (Phe).

Why it's right: The chart shows UUU codes for Phenylalanine (Phe).

Why the others miss:
  • B: Methionine is AUG, not UUU.
  • C: Tryptophan is UGG, not UUU.
  • D: The stop codons are UAA, UAG, and UGA, not UUU.

Aligned to BRE: codon lookup · reading level ~grade 9

Where you'd see this
  • In Unit 2.2 Decoding a Diagnosis, this skill turns class evidence into a result another person can check.
Careers that use this
Biological Technician: Looks up codons on a chart to confirm which amino acids a sequenced gene produces.
Video library
Watch: Read A Codon Chart
How to Read a Codon Chart
Amoeba Sisters · 5 min
Guided notes

Fill these in as you work through the lesson.

Big idea: A codon chart turns three-base mRNA codons into amino acids; AUG is the start codon, and UAA, UAG, and UGA are stop codons that end the protein.
Key terms: write the meaning
  • Codon (three mRNA bases):  
  • Codon chart (the key from codon to amino acid):  
  • Start codon (AUG (Met)):  
  • Stop codon (UAA, UAG, or UGA):  
  • Reading frame (where you start grouping the bases):  
The rule

Read the mRNA in groups of   bases. The codon   means start (Methionine). The codons UAA, UAG, and   all mean stop.

Check yourself
  1. Which codon both starts a protein and codes for methionine? 
  2. Name the three codons that mean stop. 
  3. If you start reading at a different base, why do you get different codons? 
Work one example

Look up UUU on the chart and name the amino acid; then say what UAA does. (Answer: UUU = Phenylalanine; UAA = stop, which ends the protein.)