Genome complexity: alternate reading frames (Introduction)

by David Turell @, Thursday, August 15, 2019, 02:14 (113 days ago) @ David Turell

The DNA spirals read in opposite directions which increases the information carried:

Be sure to look at the illustration


"When you talk about the complementary strand you are talking about the same chromosome, but the opposite strand of DNA. DNA is made up of two strands of nucleotides running in opposite directions, and coiled about each other, the so called double helix. One strand has typically been called the coding strand because nearly all genes were thought to be encoded on that strand.

"But as techniques for detecting transcripts have gotten better, and scientists have begun to scan for “alternative reading frames,” they are finding them.

"If you look at the figure at the top of this post,you’ll see the sequence of DNA from a human mitochondrion: AAATGAACGAAA and so on. Above in red you see the nucleotides (ATCG) have been grouped in threes, and a letter assigned to each. Each group of three is a codon, and each unique codon specifics a particular amino acid, indicated by the red letters: K W T K I, etc. That is the protein sequence that the DNA specifies for that particular way of reading the DNA. That way of reading the DNA, with that set of groups of three, is called a reading frame, because it establishes the frame for the way we read the information in the gene. In this case it encodes the protein ATP8.

"If DNA were a human code, then it would be inconceivable to have a code that could be read in more than one frame at a time. By this I mean starting at one nucleotide and getting one sequence and starting at another nucleotide and getting another sequence with a different meaning.

"But that is exactly what happens in this stretch of mitochondrial DNA. Look below the nucleotides to a different set of letters in blue. Notice that they are offset from the first reading frame by two nucleotides. This changes the way the nucleotides are read. The first codon is ATG, the second AAC, and so on. And the resulting protein, ATP6, has a very different sequence from that of the first, ATP8.

"And for toppers it is also possible to start on the complementary strand and get yet another reading in the opposite direction. Theoretically it is possible to have a code that reads in all six frames, three forward and three reverse. We see overlapping genes in everything from viruses to humans, sometimes offset from each other on the same strand, and sometimes from the complementary strand.

"So in answer to your question, yes, it is possible to get some protein from the complementary strand as well as the “coding strand.” You can have more than one protein produced from the same stretch of DNA — and I haven’t even mentioned splicing yet… but I’ll leave that for another time.

"This is amazing! Here we have multiple meanings being read from one stretch of digital code. Here it is A T C G combinations, but on a computer it would be 01001, etc. Can anyone write a string of 0s and 1s that can be read in different frames and have each of those readings make sense?

"Only a design genius could do it."

Comment: Yes, only a designing cause is capable of this magnificent complexity of a code. This is taken from an author's answer to a question.

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