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An open reading frame (ORF) is a reading frame that has the potential to be transcribed into RNA and translated into protein. It requires a continuous sequence of DNA which may include a start codon, through a subsequent region which has a length that is a multiple of 3 nucleotides, to a stop codon in the same reading frame.
In molecular biology, reading frames are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible reading frames will be "open" (the "reading", however, refers to the RNA produced by transcription of the DNA and its ...
An mRNA molecule is said to be monocistronic when it contains the genetic information to translate only a single protein chain (polypeptide). This is the case for most of the eukaryotic mRNAs. [24] [25] On the other hand, polycistronic mRNA carries several open reading frames (ORFs), each of which is
The code itself is considered degenerate, meaning that a particular amino acid can be specified by more than one codon. However, a shift of any number of nucleotides that is not divisible by 3 in the reading frame will cause subsequent codons to be read differently. [5] This effectively changes the ribosomal reading frame.
A reading frame is defined by the initial triplet of nucleotides from which translation starts. It sets the frame for a run of successive, non-overlapping codons, which is known as an "open reading frame" (ORF). For example, the string 5'-AAATGAACG-3' (see figure), if read from the first position, contains the codons AAA, TGA, and ACG ; if read ...
The first codon establishes the reading frame, whereby a new codon begins. A protein's amino acid backbone sequence is defined by contiguous triplets. [6] Codons are key to translation of genetic information for the synthesis of proteins. The reading frame is set when translating the mRNA begins and is maintained as it reads one triplet to the ...
Another form of translational regulation in eukaryotes comes from unique elements on the 5′ UTR called upstream open reading frames (uORF). These elements are fairly common, occurring in 35–49% of all human genes. [17] A uORF is a coding sequence located in the 5′ UTR located upstream of the coding sequences initiation site.
Once the start of the leader open reading frame has been transcribed, RNA polymerase pauses due to folding of the nascent mRNA. This programmed arrest of transcription gives time for translation of the leader peptide to commence, and transcription to resume once coupled to translation.