8 Difference Between Start Codon and Stop Codon (With Table)

Genetic code has instructions responsible for the synthesis of specific proteins. The gene code contains a trinucleotide sequence also known as a codon.

Each codon helps to specify the type of amino acid. Keep in mind that amino acids are the building blocks of proteins. The genetic code has a start codon and stops codon for each gene code.

So, what is the main difference between the start codon and stop codon? The former is a codon that marks the beginning of a sequence that translates into protein while the latter is a codon that marks the end of the sequence that translates into protein.

Understanding how these gene codons works are quite important. This article provides a detailed explanation of the differences between start and stops codons.

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Comparison Table (Start Codon vs Stop Codon)

Basic Terms	Start Codon	Stop Codon
Description	It is a trinucleotide sequence that marks the beginning of a sequence that translates into protein.	It is a trinucleotide sequence that marks the end of a sequence that translates into protein.
Location	First codon at the 5^th end of the transcribed mRNA	At the 3^rd end of the transcribed mRNA
Base	A-U-G	U-A-G, U-A-A, U-G-A
Significance	Marks the beginning site of the translation of the transcribed mRNA into a protein.	Marks the site at which translation ends. It also releases the newly formed polypeptide chain from the ribosomes.
Coding for an Amino acid	Yes.	Do not code for an amino acid
Open Reading Frame	Contain start codon	Do not contain stop codon
TRNA with Anticodons	Present	Absent
Ribosomes	Starts the formation of the polypeptide chain	Pauses the formation of the polypeptide chain

What Is the Start Codon?

It is the first codon of the transcribed mRNA sequence that translates into an amino acid by the ribosomes. These codons mark the site where translation into proteins commences.

The sequence comprises three nucleotides. The tRNA recognizes the start codon and commences the translation. A-U-G is the most common start codon.

The start codon helps to specify the amino acid methionine in eukaryote genes and formyl methionine in prokaryote genes.

Other alternatives to start codons in humans are CUG, AUA, and AUU while prokaryotes include GUG and UUG.

What Is the Stop Codon?

It is a trinucleotide sequence that marks the site at which translation of the mRNA into proteins ends. It is regarded as the last codon of transcribed mRNA.

Examples of stop codons are UAG, UAA, and UGA. These types of stop codons are also known as amber (UAG), opal or umber (UGA), and ochre (UAA).

The stop codon mainly signifies the end of protein synthesis. The codon is also known as a termination codon or nonsense codon.

Stop codons are responsible for releasing new polypeptide chains formed from the ribosomes. They do not code for an amino acid.

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Main Difference between Start Codon and Stop Codon

Start codon base is AUG. Stop codon bases are UAG, UAA, and UGA.
Start codon has tRNA anticodon. Stop codon lack tRNA anticodon.
Start codon has an open reading frame. Stop codon lack open reading frame.
Start codon ribosome begins the formation of the polypeptide chain. Stop codon ribosomes pauses the formation of the polypeptide chain.
Start codon enhances coding for an amino acid. Stop codon does not code for an amino acid.

Similarities Between Start Codon and Stop Codon

Both are crucial punctuation marks in genetic code.
Both are trinucleotides in mRNA.
Both are crucial in minimizing errors.

In Conclusion

Both start codon and stop codons are punctuation marks for genetic code. These codons play a crucial role during protein synthesis.

The main difference between the start codon and stop codon is that start codon marks the site at which translation sequence into protein begins while stop codon marks the site at which translation sequence into protein ends.

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