Coding sequences (CDS) are found in genes. It consists of all the exons in the gene and the start and stop codons. The true gene is what is translated and responsible for producing the protein.
A nucleotide sequence known as an open reading frame (ORF) is located between the start codon and the stop codon. The genetic code is translated into a protein and is not interrupted by a stop codon within an ORF. The CDS and ORF of a gene are identical in prokaryotes.
Identifying coding sequences in DNA is not very straightforward since the cell does not translate all open reading frames to proteins. Only a subset of all ORFs gets translated to proteins.
Table of Contents
- CDS (Coding Sequence)
- ORF (Open Reading Frame)
- Difference between CDS (Coding Sequence) and ORF (Open Reading Frame)
- Frequently Asked Questions (FAQs)
CDS (Coding Sequence)
The region of the gene which translates a gene into a protein is called the coding sequence or CDS. It consists of stop codons, the start codon (AUG) and exons. The 5′ UTR and 3″ UTR are two UnTranslated regions absent in CDS. Introns are also excluded from CDS.
Coding sequences represent a small portion of the entire genome of an individual. The nucleotide sequence required to create the amino acid sequence of a protein is included in the coding sequence.
ORF (Open Reading Frame)
The open reading frame (ORF) is the continuous segment of a nucleotide sequence that begins with a start codon and ends with a stop codon. The nucleotide sequence between the start and stop codons is the ORF. No stop codon interrupts the ORF in between. Amino acids are encoded by the sequence of nucleotides between the start and stop codons.
ATG is the start codon, and TAG, TAA, and TGA are the usual stop codons. When translated and transcribed, ORF produces a useful protein. Thus, ORF has a start codon, multiple codons in the middle, and a stop codon. The length of ORF is divisible by three as each codon is a sequence of three nucleotides. In a stretch of DNA, there can be six reading frames, three in one direction and three in the other direction. There is no certainty that an ORF actually codes for a protein.
Since prokaryotes lack introns, an ORF is the gene’s coding sequence that undergoes direct mRNA transcription. Thus, in prokaryotes, CDS and ORF are similar. It is easy to identify an ORF and locate a gene in prokaryotes.
Since eukaryotes possess introns, the ORF is the codon sequence that results from processing or RNA splicing. As long as ORF is likely to be a component of a gene, it serves as evidence supporting gene prediction.
Difference between CDS (Coding Sequence) and ORF (Open Reading Frame)
|
CDS (Coding Sequence) |
ORF (Open Reading Frame) |
| CDS is the real part of the gene translating into a protein | ORF is the segment of DNA between the start codon and the stop codon |
| It gets translated into a protein | Not all ORFs get translated into proteins |
| The entire coding region is included | It might not be the entire coding region, particularly in eukaryotes |
All CDSs (Coding Sequence) are ORFs (Open Reading Frames). However, not all ORFs are CDSs. Thus, this encapsulates the distinction between CDS and ORF.
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