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20 votes
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Why aren't 'exons' named 'introns'?

The terms intron and exon were coined by Walter Gilbert in a renowned 'News and Views' article, Why Genes in Pieces, published in the journal Nature in 1978. Introns are the intragenic regions and ...
user338907's user avatar
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12 votes
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Why is thymine not incorporated into mRNA?

Nice question! But sadly, it comes under the category of questions about which we don't know everything yet. We don't yet know how RNA Polymerase differentiates between uracil and thymine while adding ...
another 'Homo sapien''s user avatar
11 votes

From which end of mRNA does transcription start?

They're both correct. The confusion stems from the book talking about the anticoding strand as well as the newly-formed coding RNA strand, whereas Khan Academy talks only about the coding strand. ...
Thymine's user avatar
  • 259
11 votes

why does translation occur more frequently than transcription?

The simple answer Under the assumption that each mRNA molecule is translated at least once, by necessity translation will happen more often than transcription. This is because the only way to get a ...
Maximilian Press's user avatar
10 votes
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Why doesn't RNA polymerase just rotate?

Consider that: RNA polymerase (RNAP) is a large complex (~400 kDa in bacteria); inertia and drag would hinder its rotation. RNAP is attached to its RNA transcript, which becomes increasingly large as ...
canadianer's user avatar
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9 votes
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How do DNA, enzymes, hormones etc. reach their proper cellular locations?

The answer given by Sadegh gives a general correct broad view. But one part of the puzzle is missing, which is molecular recognition. Molecules bind to each other via physical/chemical interaction ...
alec_djinn's user avatar
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9 votes
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Is alternative splicing possible in the same cell?

In complex eukaryotes like humans, alternative splicing is the rule, rather than the exception. Eukaryotic splicing is managed by a complex regulatory system, including more than 100 different ...
jakebeal's user avatar
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7 votes
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DNA & mRNA During Transcription

Transcription occurs in a special structure known as transcription bubble. Inside the bubble are present the mRNA, template DNA being transcribed and the RNA Polymerase. Upstream of bubble is the DNA ...
another 'Homo sapien''s user avatar
7 votes

How do cells relocate transmembrane proteins from one side of the cell to the other? Is it possible?

The breakdown and reassembly of proteins is a ubiquitous process within cells, and yes this is expensive but transport is expensive, too, and recycling has the added benefit of dealing with proteins ...
Bryan Krause's user avatar
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7 votes

How do DNA, enzymes, hormones etc. reach their proper cellular locations?

It's both simple and complex. The simple answer is Brownian motion. All the particles in the cell do have mobility which is related to their mass. A small particle like a soluble enzyme undergoes ...
Sadegh Ghasemi's user avatar
7 votes
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From which end of mRNA does transcription start?

@Thymine's answer is correct. I just thought I'd post a more graphic answer for clarity. ...
rotaredom's user avatar
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7 votes
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Correct description of ALDH7A1 and other genes

It's the second: The RNA transcript of the gene (before editing) has a length of 4964 bases. The use of "base pairs" is wrong in this context since the transcribed RNA has no paired bases. ...
Chris's user avatar
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6 votes
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Do transcripts always start and end with exons?

Most (almost all, AFAIK) mRNAs and lncRNAs start with exons for the reasons already mentioned by David. In a typical splicing event, the nucleotide that is 5' to the splice donor site (lets call it ...
WYSIWYG's user avatar
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6 votes

Is the transcription starting site located before or after the promoter?

Just in addition to David's answer, there are examples of internal promoters (those which have elements 3' of the transcription start site). As an example, internal promoter elements of tRNA genes ...
canadianer's user avatar
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6 votes
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RNA polymerase and DNA helicase

Disclaimer As I have pointed out in my comment, it is not clear whether the sources mentioned relate to eukaryotes or prokaryotes, assuming they are correct. I am a translation man, rather than a ...
David's user avatar
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6 votes

RNA polymerase Sigma subunit: transcription factor, coenzyme, or what?

No. I don’t think anybody would call the sigma factor of bacterial RNA polymerase — or indeed any other protein — a cofactor or a coenzyme, the subset of cofactors that are organic (the original ...
David's user avatar
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6 votes
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How to memorize Transcription and Translation?

I prefer a conceptual distinction rather than a mnemonic in this case. I've always thought of a transcript as an exact copy of record - that's the meaning of the word in English, and an RNA transcript ...
Bryan Krause's user avatar
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6 votes

Does a gene need to be transcribed for every single protein made?

mRNA is not destroyed immediately after it is translated once. There can be multiple ribosomes translating a single strand of mRNA, as well. Depending on the regulation of the system, a single ...
MattDMo's user avatar
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5 votes
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Are all prokaryotic promotor regions the same, or do they differ depending on the product of the transcript?

Definitely not. There is a ton of variation from gene to gene, otherwise, as you say, regulation wouldn't work. That said, the word "promoter" sometimes gets used in different ways. Especially in ...
Victor Chubukov's user avatar
5 votes
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Is there selection against long proteins and long genes?

Is there evidence of selection against long proteins and long genes? I am not aware of any such evidence and cursory googling did not reveal studies that researched a correlation between gene ...
Thawn's user avatar
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5 votes
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On which DNA strand is TATA box present?

TATA box is a feature of organisms that have dsDNA as a genetic material. Like most dsDNA promoter elements, TATA box is basically a section of dsDNA. However a question like "On which DNA strand is ...
WYSIWYG's user avatar
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5 votes
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How do cells relocate transmembrane proteins from one side of the cell to the other? Is it possible?

Transmembrane proteins can move laterally through the plasma membrane (see fluid mosaic model) and this movement can be actively directed along the cytoskeleton. The following paper is the most ...
canadianer's user avatar
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5 votes
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How to find the amino acid in the DNA protein

Then you just have to read the codon until you reach a stop codon. There are three stop codon UAA, UGA and ...
Remi.b's user avatar
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5 votes

What makes/breaks the hydrogen bonds between DNA and RNA during transcription?

I wouldn't really say RNA polymerase is "creating" the hydrogen bonds so much as it's thermodynamics that creates them. When we talk about an enzyme "creating" a bond, what we're generally referring ...
Stephen B.'s user avatar
5 votes

What percentage of our DNA is never transcribable? What percent is never actually transcribed into RNA unless researchers force it to in a lab?

While, as you say, most of our DNA can be transcribed, you are right that it is not well accessible and/or lacks strong promoters. It's said that over 80% of DNA is transcribed but only <2% ...
KaPy3141's user avatar
  • 1,597
4 votes

difference between transcriptional activator and general transcription factors?

Activators turn genes on - they help or promote RNA transcription of the gene. Other Transcription factors may turn genes off (prevent or reduce RNA transcription). Some transcription factors may ...
shigeta's user avatar
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4 votes
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Relationship of the DNA of a eukaryotic gene to the 5'-UTR of its mRNA

Concise Answer The 5′-UTR region of a eukaryotic mRNA is derived from the RNA transcript of the region of a gene between the transcription start site and the DNA corresponding to the translational ...
David's user avatar
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4 votes

Why is thymine not incorporated into mRNA?

The answer to this question is quite straightforward: Thymine is not incorporated into mRNA because the precursors of RNA synthesis are ribonucleoside triphosphates (not the free bases) and ...
David's user avatar
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4 votes
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When does histone synthesis occur in relation to DNA replication?

Yes, they have to. But that is just half of the story. The (canonical) histones which are used in DNA replication are synthesized at the beginning of the S phase, and subsequently transported into ...
adjan's user avatar
  • 2,106
4 votes
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Is the transcription starting site located before or after the promoter?

You will find the answer to this question in any standard text book of Biochemistry, Molecular Biology or Molecular Genetics. There are several on-line at NCBI bookshelf, and these are generally far ...
David's user avatar
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