1) TATA box is on the non-coding strand?
Usually we make mention about promoter being upstream of the gene in question, then we talk about TATA box sequences. You can take promoter as a region upstream but when we try to dissect the issue of "where is the TATA sequence? On which strand can it be found?"...the answer is as above. (check out the picture in your notes).
Non-coding strand - non-template strand = the strand that is complementary to the one used to transcribe for mRNA.
If you are a visual person, do not confuse this with DNA replication. In DNA replication, you can have two DNA polymerases on each strand. But in transcription, RNA polymerase is a huge molecules that take both strands into account and recognise the TATA box before unwinding and separating the strand for transcription. These pictures may help
2) adenine is related but is not equivalent of adenosine?
Adenine is the purine as we know.
ribose+adenine = adenosine
deoxyribose + adenine = deoxyadenosine
adenosine triphosphate = adenosine with 3 phosphate grps.
3) * Extra * Extra
Transcription factors can be further categorized into two types: general & specific.
General TF will bind to promoter.
Specific TF will bind to other control elements.
It is general because promoters are quite typical so the same grp of TF is applicable for all. Finer control comes with the specific TF.
Question for today for you to ponder: How do you ensure that genes are not transcribed until required?
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7 comments:
Hi Mr Chan,
Isn't the non-template strand the CODING strand? It has the same base sequence as the mRNA strand (except for the Us and the Ts)
Sorry, got confused by your post.
can i check where that info stem from?
US and UK books have the two terms in the exact opp ways.
To adhere to UK, we teach that the template strnd of DNA as coding strand. non-template as non-coding strand - which is why i have informed during lecture to make the necessary changes to the diagram in the notes for consistency.
And yes the non-template strand will have the same base seq as the mRNA
- mr chan
Question for today for you to ponder: How do you ensure that genes are not transcribed until required?
Let me try some answers:
1) In eukaryotes, the state of methylation of the histone proteins regulates the packing of DNA such that only genes found in decondensed DNA (euchromatin) is actively transcribed as RNA polymerase has access to the genes. An extreme example is the condensation of one of the two X chromosomes in females of the XY sex determinatin system to form the Barr body so that genes on the Barr body are not transcribed and hence not expressed. The level of condensation of DNA could be influenced by extracellular molecular signals which are transduced to increase/decrease the activity of enzymes that catalyse the methylation of histone proteins.
2) The operon system of gene regulation is present in most prokaryotes and some eukaryotes. The reversible binding of a repressor molecule to the operator disallows the binding of RNA polymerase to the promoter region of a gene, hence preventing the transcription of the gene.
3) The effect of transduction of extracellular molecular signals activates/deactivates specific transcription factors (perhaps by phosphorylation?). Having fewer activated activators for the enhancers associated with one particular gene down-regulates the expression of that gene. Alternatively, more activated repressors will also down-regulate the expression of that gene. Since general transcription factors are almost universal, basal transcription is still present.
4) There could be methylation of the nucleotides of a gene especially in the promoter region, for example as in epistasis. The modified nucleotides of the promoter region are no longer complementary in shape and charge to nor recognised by the general transcription factors. Therefore RNA polymerase cannot bind to the promoter and transcription does not take place.
I'm not sure if these are the answers you're looking for :\ I'm afraid I may have accounted for up-regulation vs. down-regulation of gene transcription instead of the absolute on-off state of genes.
I believe the effect of extracellular molecular signals is the most significant with regard to the control of the expression of different genes at different times and in different cells during the development of a multicelluar organism.
Note: I'm not the person who originally asked this question. I just happened to see the comment and I remembered checking campbell before.
I refer to BIOLOGY, Campbell & Reece, 7th Edition, page 313 (top right hand corner). It's a US book though.
The term codon is also sometimes used for the DNA base triplets along the nontemplate strand. These codons are complementary to the template strand and thus identical in sequence to the mRNA except that they have T instead of U. (For this reason, the nontemplate DNA strand is sometimes called the "coding strand.")
I think to prevent confusion, we should not use in our writing the terms "coding" and "non-coding" (I know I don't because I get confused) and instead use "template" and "non-template" which I believe is unambiguous. However, will Cambridge use the terms "coding" and "non-coding" and if so, which strands are they refering to?
Thanks
yep i checked campbell and several other websites.
i know, i use template and non-template to be safe. just that this question has been raised many times.
ok I am getting a bit bugged by anonymous pple! How many pple do we know are called anonymous ahahhaah. I think i know who wrote the first msg but after that it is just so confusing. Kindly pls leave your wonderful initial or some form of id k?
I think I have already mentioned what term to use so stix to it yah? Nonetheless I would not call sequences on the DNA codon even in triplet. codon is a term I will leave for reading the mRNA.
haha thanks anyway mr chan. i posted the original post and i am not from your class. so you wouldn't know me. i think. :)
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