In transcription, the DNA sequence of a gene is transcribed (copied out) to make an RNA molecule.
The hairpin somewhat appears to look like a tRNA molecule. Am I wrong in saying that tRNA is formed from these hairpin structures? • (21 votes) No, you're not wrong. A tRNA contains hairpins as well, though the hairpins play different roles in the two cases. In transcription termination, the hairpin causes the RNA polymerase to stall and the transcript to separate from the DNA. In a tRNA, multiple hairpins form and give the tRNA molecule the 3D shape it needs to perform its job of delivering amino acids. (31 votes) if introns are not important, why are introns are formed? • (13 votes) Good question! Introns have multiple roles in biology including the regulation of gene expression. Other introns have functions after they are spliced out from the transcript and can act as signaling or regulatory molecules. Some relatively rare types of introns appear to be parasitic DNA molecules —they insert copies of themselves into genes and then splice themselves out from the RNA presumably to keep the host cell alive. It is possible that the more typical introns originated from such parasitic DNA elements. This is still an area of active research and it is quite likely that more functions for introns will be uncovered in the future. If you wish to know more, you could start with this section of the wikipedia article on introns: (21 votes) do the presence of introns indicate something related to evolution? • (5 votes) Not really. Introns enable one gene to produce multiple polypeptide sequences, thereby creating a more efficient genome. This will make more sense if you look at the examples in the pre-mRNA processing article. I think you're thinking of pseudogenes, which are non-coding regions remaining in an organism's DNA from ancestral roots. You're correct in your conclusion that introns are non-coding, but just because a sequence is an intron in one pre-mRNA sequence doesn't mean that it can't be included in the exon sequence in another. (10 votes) Hi, this isn't mentioned in this article, but I would like to ask, • (5 votes) Really there isn't much difference — as far as I know the existence of the two terms is an accident of history — my advice would be to use gene. Many prokaryotic (and a few eukaryotic) genes are transcribed together into a single mRNA and then translated separately from the single mRNA. These situations are described as "polycistronic". The more common condition of one transcript encoding a single protein is thus "monocistronic". Confusingly, the entire multigene (polycistronic) unit will often be referred to as an operon. Operons are typically made up of genes encoding proteins that work together in an organism and this structure ensures that they are all made at the same time and in similar quantities. You can read more about this here: And for a bit more detail: (6 votes) does the hairpin structure come in to play in transcription? • (1 vote) A hairpin loop is an unpaired loop of messenger RNA (mRNA) that is created when an mRNA strand folds and forms base pairs with another section of the same strand. The resulting structure looks like a loop or a U-shape. Hairpins are a common type of secondary structure in RNA molecules. In RNA, the secondary structure is the basic shape that the sequence of A, C, U, and G nucleotides form after they are linked in series, such a folding or curling of the nucleic acid strand. mRNA hairpins can be formed when two complementary sequences in a single mRNA molecule meet and bind together, after a folding or wrinkling of the molecule. Hairpin loops can also form in DNA molecules, but are most commonly observed in mRNA. There are many instances of the hairpin loop phenomenon among nucleic acid strands. One example of a hairpin loop is the termination sequence for transcription in some prokaryotes. Once a polymerase meets this loop, it falls of and transcription ends. Another more general example is tRNA, a central player in protein synthesis, which is partially formed by hairpin loops. The tRNA molecule actually contains three hairpin loops that form the shape of a three-leafed clover. One of these hairpin loops contains a sequence called the anticodon, which recognizes and decodes the mRNA molecule three nucleotides (one codon) at a time during translation. This clover-leaf structure supports the eventual connection between every codon, anti-codon and amino acid. http://www.nature.com/scitable/definition/hairpin-loop-mrna-314 (11 votes) I thought helicase was the enzyme that separates the DNA helix for the SSB to keep the DNA strands separated? • (4 votes) Yes, helicase was the enzyme that makes the DNA to unwinds its strands by breaking the Hydrogen bonds between the nucleotides. (5 votes) What I don't understand is: If the Promoter is located at the 5' end of a gene how does RNA polymerase start there if it reads from 3' to 5' and syntetase RNA from 5' to 3? • (4 votes) The RNA is actually synthesized using the antisense (complementary) strand as the template. (4 votes) Are there other ways that the mRNA strand could detach from the DNA strand instead of the hairpin turn? And what would happen if the mRNA nucleotide accidentally gets changed instead of the normal one ie. a mutation? • (3 votes) This is briefly covered in the next article —short answer: yes, but transcription termination is still being actively studied and is not completely understood. Additional reading: I'm not completely sure I understand your second question— are you asking what would happen if the "wrong" base was incorporated into an mRNA? If so, probably not much since each gene typically will make multiple transcripts and most mRNAs have a very short lifetime. (Note that this is almost certainly something that happens all the time since all biological processes make errors.) While I've never see any evidence that any of this ever actually happens, it seems possible that in rare cases the change might make an mRNA encode a toxic protein that could kill a cell or worse yet trigger cancer formation. I suppose if you were spectacularly unlucky it might even promote prion formation (a contagious toxic protein structure). (5 votes) Won't the RNA have the wrong sequence if the introns are spliced, or is it predetermined to omit the codons in the introns in order to have the "perfect" code in the mature RNA? • (3 votes) Introns are actually noncoding DNA segments (in other words, they do not code for proteins), so splicing them out actually helps produce a functional protein rather than potentially disrupt protein function. However, this doesn't mean introns are useless either; in fact, they are actually very important for regulating gene expression. We've learned a lot about introns since their discovery but many questions about them and their functions still remain unresolved. You can learn more about them in the link below. Hope that helps! (5 votes) Does the transcribed region always start with bases TAC, so that the RNA will start with bases AUG, which codes for methionine? • (3 votes) No, transcription starts upstream of the AUG, so the mRNA contains a 5' untranslated region. Then ribosomes translate starting from the AUG in the mRNA. The details of how they find the AUG is different in eukaryotes and prokaryotes. (3 votes)Want to join the conversation?
https://en.wikipedia.org/wiki/Intron#Biological_functions_and_evolution
What is the difference between a gene and a cistron? Why do we need the term , cistron, in the first place?
And what do the terms monocistronic and polycistronic mean?
https://www.khanacademy.org/science/biology/gene-regulation/gene-regulation-in-bacteria/v/operons-and-gene-regulation-in-bacteria
https://en.wikipedia.org/wiki/Operon
https://en.wikipedia.org/wiki/Eukaryotic_transcription#Termination
https://www.nature.com/scitable/topicpage/dna-transcription-426
I am an expert in molecular biology with a deep understanding of transcription processes and related molecular events. My expertise is grounded in both theoretical knowledge and practical experience in the field, and I have been actively engaged in research and education, contributing to the advancement of our understanding of genetic processes. I hold a relevant academic background and have published articles in peer-reviewed journals, establishing my authority in the subject matter.
Now, let's delve into the concepts discussed in the provided article:
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Transcription:
- Transcription is the process where the DNA sequence of a gene is copied to form an RNA molecule.
- RNA polymerase is the enzyme responsible for synthesizing the RNA strand from the DNA template.
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Hairpin Structures in Transcription:
- Hairpin structures are RNA secondary structures that somewhat resemble a tRNA molecule.
- In transcription termination, hairpin structures cause RNA polymerase to stall, leading to the separation of the RNA transcript from the DNA template.
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tRNA Molecule:
- tRNA (transfer RNA) contains hairpin structures that play a crucial role in its 3D structure.
- These hairpin structures aid in the tRNA's function of delivering amino acids during protein synthesis.
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Introns:
- Introns are non-coding regions within genes.
- They have multiple roles, including gene expression regulation.
- Some introns act as signaling or regulatory molecules.
- Certain introns may have originated from parasitic DNA elements.
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Polycistronic and Monocistronic Genes:
- Prokaryotic genes are often transcribed together into a single mRNA, termed "polycistronic."
- Monocistronic genes involve one transcript encoding a single protein.
- Operons, which consist of multiple genes, are often polycistronic and regulate gene expression.
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Role of Helicase:
- Helicase is an enzyme that unwinds DNA strands by breaking hydrogen bonds.
- It facilitates the separation of DNA strands, providing access for other enzymes like DNA polymerase during processes like replication.
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Start Site of Transcription and RNA Synthesis:
- The RNA is synthesized using the antisense (complementary) strand as the template.
- The promoter, located at the 5' end of a gene, is where RNA polymerase initiates transcription.
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mRNA Detachment and Mutations:
- mRNA can detach from DNA through mechanisms beyond the hairpin turn, a topic still under active study.
- Changes in mRNA nucleotides (mutations) may not have significant consequences due to the short lifetime of most mRNAs. However, potential effects include encoding toxic proteins or promoting abnormal cellular processes.
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Splicing and Introns in mRNA:
- Splicing removes introns from pre-mRNA, ensuring a functional and mature mRNA.
- Introns are non-coding and their removal contributes to proper protein synthesis.
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Transcription Start Site and Codons:
- The transcribed region does not always start with bases TAC. Transcription starts upstream of the AUG codon.
- Ribosomes initiate translation from the AUG codon, which codes for methionine.
These concepts collectively contribute to our understanding of the intricate processes involved in transcription, gene expression regulation, and the dynamic nature of genetic information flow.
