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Start Codon vs. Stop Codon — What's the Difference?

By Tayyaba Rehman — Published on November 30, 2023
The start codon signals the beginning of protein synthesis, typically "AUG," while stop codons signal its termination, like "UAA," "UAG," or "UGA."
Start Codon vs. Stop Codon — What's the Difference?

Difference Between Start Codon and Stop Codon

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Key Differences

The start codon plays a crucial role in protein synthesis, marking where translation should commence. The stop codon, conversely, indicates where this process should end.
Tayyaba Rehman
Nov 30, 2023
When ribosomes read mRNA during translation, they identify the start codon as the initiation point. The stop codon, on the other hand, instructs ribosomes to release the newly formed polypeptide.
Tayyaba Rehman
Nov 30, 2023
In the genetic code, while there's only one primary start codon, which is "AUG," there are three primary stop codons: "UAA," "UAG," and "UGA."
Tayyaba Rehman
Nov 30, 2023
Interestingly, the start codon not only signals the beginning of translation but also codes for the amino acid methionine. In contrast, stop codons do not code for any amino acid.
Tayyaba Rehman
Nov 30, 2023
As molecular biology evolved, it became evident how crucial these codons are: the start codon ensures accurate protein synthesis initiation, and the stop codon ensures proper termination, preventing unnecessary amino acid additions.
Tayyaba Rehman
Nov 30, 2023
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Comparison Chart

Function

Initiates protein synthesis
Terminates protein synthesis
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Nov 30, 2023

Common Codon

AUG
UAA, UAG, UGA
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Coded Amino Acid

Methionine
None
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Number in Genetic Code

Primarily one
Three
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Role in Translation

Signals ribosome to start
Signals ribosome to release polypeptide
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Nov 30, 2023

Compare with Definitions

Start Codon

Its presence is vital for the accuracy of protein synthesis.
Without the start codon, ribosomes wouldn't know where to begin translating.
Tayyaba Rehman
Oct 10, 2023

Stop Codon

There are three primary stop codons: UAA, UAG, and UGA.
The sequence UGA is one of the three stop codons used in genetic code.
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Oct 10, 2023

Start Codon

In eukaryotes, the start codon is located at the 5' end of mRNA.
The ribosome scans the mRNA and starts translation once it finds the start codon.
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Oct 10, 2023

Stop Codon

Their presence ensures the proper termination of translation.
An absence of the stop codon could lead to a dysfunctional protein.
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Oct 10, 2023

Start Codon

This codon also codes for the amino acid methionine.
When translation begins with the start codon, methionine is the first amino acid added.
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Oct 10, 2023

Stop Codon

Unlike other codons, stop codons don't code for amino acids.
The protein synthesis halts when a stop codon is reached, and no amino acid is added.
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Oct 10, 2023

Start Codon

Start codon is the mRNA sequence signaling protein synthesis initiation.
The ribosome recognizes the start codon and begins translation.
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Oct 10, 2023

Stop Codon

Recognized by release factors in translation.
When a stop codon is read, release factors facilitate the termination of translation.
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Oct 10, 2023

Start Codon

It is typically represented as "AUG" in mRNA.
In most organisms, AUG serves as the universal start codon.
Tayyaba Rehman
Oct 10, 2023

Stop Codon

Stop codons are mRNA sequences that signal the end of protein synthesis.
When the ribosome encounters a stop codon, it releases the polypeptide chain.
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Oct 10, 2023

Common Curiosities

Where does the ribosome start translating mRNA?

It starts at the start codon, typically AUG.
Tayyaba Rehman
Nov 30, 2023

Do stop codons code for any amino acid?

No, they don't code for any amino acid.
Tayyaba Rehman
Nov 30, 2023

What is the primary function of the start codon?

It signals the initiation of protein synthesis during translation.
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Nov 30, 2023

How many stop codons are there?

There are three primary stop codons: UAA, UAG, and UGA.
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Nov 30, 2023

How does translation terminate?

When a ribosome encounters a stop codon, translation ends.
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Nov 30, 2023

Is the start codon the same across all organisms?

While there are exceptions, AUG is generally the universal start codon.
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Nov 30, 2023

Can mutations in the stop codon affect protein synthesis?

Yes, mutations can lead to longer, often nonfunctional proteins.
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Nov 30, 2023

Does the start codon also represent an amino acid?

Yes, it codes for the amino acid methionine.
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Nov 30, 2023

Why are stop codons essential?

They ensure proper termination of translation, preventing extended, nonfunctional proteins.
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Nov 30, 2023

Can stop codons be found in the middle of a gene?

Normally, no. But mutations can introduce premature stop codons, often causing diseases.
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Nov 30, 2023

Is "AUG" the only start codon?

It's the primary one, but in rare cases, other codons can initiate translation.
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Nov 30, 2023

What happens if a start codon is mutated?

Protein synthesis might not initiate, leading to nonproduction or misproduction of a protein.
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Nov 30, 2023

How does the cell "read" the start and stop codons?

Ribosomes "read" these codons during the process of translation.
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Nov 30, 2023

Are there proteins associated with recognizing the stop codon?

Yes, release factors recognize stop codons and facilitate translation termination.
Tayyaba Rehman
Nov 30, 2023

If the start codon initiates translation, why is it also associated with an amino acid?

It ensures that every protein begins with methionine, which can be essential for protein targeting and other functions.
Tayyaba Rehman
Nov 30, 2023

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Author Spotlight

Written by
Tayyaba Rehman
Tayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.

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