start codon: meaning, definition, pronunciation and examples
C2 (Specialized Technical)Technical/Scientific (Molecular Biology, Genetics, Biochemistry)
Quick answer
What does “start codon” mean?
The specific sequence of three nucleotides in messenger RNA (AUG) that signals the beginning of protein synthesis during translation.
Audio
Pronunciation
Definition
Meaning and Definition
The specific sequence of three nucleotides in messenger RNA (AUG) that signals the beginning of protein synthesis during translation.
In molecular biology, the start codon initiates translation by specifying the first amino acid (methionine in eukaryotes, formylmethionine in prokaryotes) in a polypeptide chain. It establishes the reading frame for subsequent codons.
Dialectal Variation
British vs American Usage
Differences
No significant lexical differences. Spelling conventions follow standard UK/US patterns for surrounding text (e.g., 'signalise' vs. 'signalize' is possible but rare in this context).
Connotations
Identical technical meaning. The concept is universal in molecular biology.
Frequency
Equal frequency in UK and US academic/technical literature.
Grammar
How to Use “start codon” in a Sentence
The [gene/sequence] contains a start codon.Translation initiates at the start codon.The ribosome binds to the start codon.A mutation disrupted the start codon.Vocabulary
Collocations
Examples
Examples of “start codon” in a Sentence
noun
British English
- The researcher pinpointed the exact start codon in the novel gene sequence.
- A strong Kozak consensus sequence enhances recognition of the start codon.
American English
- The bioinformatics software automatically annotates the start codon.
- A frameshift mutation can create a new, out-of-frame start codon.
Usage
Meaning in Context
Business
Virtually never used.
Academic
Core terminology in molecular biology, genetics, and biochemistry papers and textbooks.
Everyday
Never used in everyday conversation.
Technical
Essential term in laboratory protocols, bioinformatics, genetic engineering, and research discussions.
Vocabulary
Synonyms of “start codon”
Strong
Neutral
Weak
Vocabulary
Antonyms of “start codon”
Watch out
Common Mistakes When Using “start codon”
- Using 'start code' instead of 'start codon'.
- Confusing it with a promoter region (which is for transcription, not translation).
- Assuming all organisms use only AUG (some prokaryotes use alternatives).
- Misspelling as 'start codone'.
FAQ
Frequently Asked Questions
While AUG is the vast majority and considered the canonical start codon, some prokaryotes and mitochondria can use GUG or UUG as alternative start codons, typically coding for methionine as well.
A promoter is a DNA sequence where RNA polymerase binds to initiate transcription (making RNA from DNA). A start codon is an mRNA sequence where the ribosome binds to initiate translation (making protein from mRNA). They are different steps in gene expression.
Yes. The start codon AUG codes for the amino acid methionine (formylmethionine in bacteria). So the first amino acid in nearly every newly synthesized protein is a methionine.
Yes. An mRNA can have multiple in-frame or out-of-frame AUG sequences. The ribosome typically initiates at the first AUG in a good context. Sometimes, under specific regulation, downstream start codons can be used to produce different protein isoforms from the same mRNA.
The specific sequence of three nucleotides in messenger RNA (AUG) that signals the beginning of protein synthesis during translation.
Start codon is usually technical/scientific (molecular biology, genetics, biochemistry) in register.
Start codon: in British English it is pronounced /ˈstɑːt ˌkəʊ.dɒn/, and in American English it is pronounced /ˈstɑːrt ˌkoʊ.dɑːn/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “None. The term is purely technical.”
Learning
Memory Aids
Mnemonic
Think of a START button on a machine. The 'start codon' is like the genetic 'START button' for building a protein.
Conceptual Metaphor
A START SIGNAL or INITIATION SWITCH in an assembly line (the ribosome is the assembly line, the mRNA is the instruction manual, and the start codon is the 'begin work here' signal).
Practice
Quiz
What is the most common start codon across all domains of life?