SONGLyrical DNA
Polymer-Racer
A song about transcription and RNA processing, told as an arcade race. The lyrics run from the promoter and the single template strand, through RNA polymerase reading in the 3-prime to 5-prime direction while building in the 5-prime to 3-prime direction, then the cap, tail, and intron excision that other enzymes carry out to produce different mature mRNA versions. Select any highlighted line to see the biology behind it.
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Interactive lyrics
Lines with a dotted underline and a + marker have an explanation. Select one and the science appears beside the lyrics. Everything else is ordinary lyric text.
Intro
POLYMER-RACER
Intro: Arcade Countdown
Single strand selected.
Three, two, one...
TRANSCRIBE!
Verse 1: Fast Precision Rap
Pre-Chorus: Direction Callout
Read it! Build it! Keep it in the lane!
Hit the checkpoint, let the hook begin!
Chorus: Stacked Hook
Polymer-Racer! Polymer-Racer!
Verse 2: Fast Precision Rap
Pre-Chorus: Direction Callout
Read it! Build it! Keep it in the lane!
Hit the checkpoint, let the hook begin!
Chorus: Stacked Hook
Polymer-Racer, one strand sets the pace,
Polymer-Racer, build it base by base.
Polymer-Racer, template in the lane,
Polymer-Racer, make that RNA chain.
Race it! Trace it! Make that messenger!
Polymer-Racer! Polymer-Racer!
Verse 3: Glitch-Rap Switch-Up
Edit mode flashing, now the splice route starts,
Bridge: Filtered Arcade Callouts
GTP cap - recognition!
Poly-A tail - stabilization!
Introns out! Retained exons splice!
Alternative versions at the finish line!
Final Chorus: Full Stack
Polymer-Racer, one strand sets the pace,
Polymer-Racer, build it base by base.
Polymer-Racer, template in the lane,
Polymer-Racer, make that RNA chain.
Race it! Trace it! Make that messenger!
Polymer-Racer! Polymer-Racer!
Polymer-Racer, one strand sets the pace,
Polymer-Racer, build it base by base.
Polymer-Racer, template in the lane,
Polymer-Racer, make that RNA chain.
Race it! Trace it! Make that messenger!
Polymer-Racer! Polymer-Racer!
Outro: Game-Over Voice
Transcript complete.
Processing complete.
POLYMER-RACER!
Concepts covered
Promoters help initiate transcriptionRNA polymerase and transcription factors bind to promoter or enhancer DNA sequences, and that binding initiates transcription. Either kind of sequence can lie upstream or downstream of the transcription start site. Live is arcade language borrowed from a game cabinet, but a promoter is not a device and not a button. It is a stretch of DNA sequence that those proteins recognize and attach to.
One DNA template strand directs transcriptionRNA polymerase uses a single template strand of DNA to direct which bases are included in the newly forming RNA molecule, and that process is transcription. The enzyme adds nucleotides one at a time, so the transcript lengthens as the enzyme advances along the strand. Track and ride are racing images for the polymerase travelling along that one strand of DNA.
Transcription transfers sequence information to RNAThe order of bases along the template strand determines the order of bases in the transcript, so sequence information passes from DNA into a new RNA molecule. That transfer is what transcription means. RNA polymerase joins RNA nucleotides into a growing chain, while the DNA is read as a template and left intact. It is not consumed and not converted into RNA.
RNA polymerase reads and synthesizes in opposite directionsRNA polymerase reads the template DNA strand in the 3-prime to 5-prime direction and synthesizes the mRNA in the 5-prime to 3-prime direction. These are two directions along strands that run opposite each other, not two speeds and not two separate processes. Each new nucleotide is added to the 3-prime end of the growing RNA, which is why the transcript builds 5-prime to 3-prime.
Eukaryotic mRNA is processed after transcriptionIn eukaryotic cells the mRNA transcript undergoes a series of enzyme-mediated modifications: a cap on one end, a tail on the other, and the excision of introns. RNA polymerase is the enzyme that carries out transcription, joining the nucleotides of the transcript itself. The capping, tailing and splicing are the work of other enzymes acting on that transcript, which is what other enzymes take the floor names.
The GTP cap supports ribosomal recognitionA GTP cap is added to the front end of a eukaryotic mRNA transcript, and that cap helps with ribosomal recognition. Recognition is the key names what the cap contributes to the molecule. The cap is a group added onto the transcript rather than a base copied from the template strand, so it is part of the finished mRNA that has no counterpart in the DNA sequence.
The poly-A tail increases mRNA stabilityThe addition of a poly-A tail makes an mRNA molecule more stable, meaning the molecule persists longer in the cell. Front and back separate the two modifications by position: the GTP cap goes on one end of the transcript and the poly-A tail on the other. They also do different jobs, since stability is about how long the mRNA lasts, not about being recognized by a ribosome.
Introns are removed and retained exons are splicedIntrons are the segments of the transcript that get excised, cut out of the RNA and discarded. Exons are the segments that are retained. Splicing is the joining step that connects the retained exons to one another so that the mature mRNA is one continuous chain of nucleotides. Spliced into line pictures those exons ending up joined end to end in a single unbroken molecule.
Alternative splicing produces mature mRNA versionsThe excision of introns, along with the splicing and retention of exons, generates different versions of the mature mRNA molecule, and that process is alternative splicing. Retaining one set of exons and joining them yields one mature mRNA; retaining a different set yields another. The gene comes through unchanged, since the DNA sequence is identical before and after and only the RNA copy is altered. More than one finish line is the racing image for those several possible versions.
Complementary base pairing sets every base in the transcriptBuilding base by base follows the pairing rules. A C on the template gives a G in the transcript, a G gives a C, a T gives an A, and an A gives a U, because RNA carries uracil where DNA carries thymine. Trace it is the misleading word here, since the transcript is complementary to the template rather than an identical copy of it.
RNA is a polymer built on one template strandA polymer is a long molecule built from many small subunits joined in a row, and an RNA chain is a polymer of nucleotides. One strand of the DNA is the template that directs which base is added at each position along that chain. Pace and lane are racing images. The template sets which base comes next rather than a speed or a competition, and the lane stands for the single strand being read.
The two DNA strands are not interchangeable templatesRNA polymerase uses one template strand to direct the bases of the new RNA, and the two strands of a DNA molecule carry different base sequences, so they are not interchangeable. Whichever strand serves as the template sets every base in the transcript. Reading the other strand would build a different RNA, with an order of bases that does not correspond to the product the gene specifies. Locked in is arcade language for committing to that one strand.
mRNA carries sequence information from the nucleus to a ribosomeMessenger RNA molecules carry information from DNA in the nucleus to the ribosome in the cytoplasm, which is the eukaryotic cell the song has been describing. There the sequence is read to build a polypeptide. Send it compresses that whole trip into two words, but nothing is fired anywhere. The DNA stays in the nucleus and the transcript travels, carrying a copy of the sequence information rather than the gene.
