Questions of the Week

Contributed by ST:

> 1) are enhancers and silencers found within or between genes?

Both are be found anywhere- in non-coding regions (betw genes) or within genes (in the introns) But we recognise that enhancers are distal elements (pretty far away from the promoter). Little is said about silencers so we gather that they do not have to be distal.


> 2) when saying that the transposable elements are repetitive DNA, does it mean that they are a long string of repeated nucleotides, e.g. CAGCAGCAGCAG or is it because there are multiple copies of transposons scattered throughout the genome (due to the copy and paste mechanism of retrotransposons) ?

Thanks for clarifying this! I noticed this while checking the notes and wanted to point this out!
Transposons does not have tandem repeat. Its basic characteristic is in its ability to jump! The notes could be clearer: the "repetitive" part is really about the many copies that can exist due to the copy and paste mechanisms of retrotransposons which so very common in us. So you are right!



> 3) "Telomeres do not exist as a free end, but as a loop - formed when the 3' single-stranded ends DISPLACES the same sequence in an upstream region of the telomere, causing a single-stranded region to form." I don't really get the bolded parts.

The 3'OH overhang will displace an identical sequences upstream (of ssDNA 1) to form complementary base-pairing with the other DNA strand (ssDNA2). The displaced single-stranded DNA (ssDNA) which of the same sequences as the 3'OH overhang is now left hanging like a hump-like structure you see in your notes because it has no one to base-pair with.

> 4) what is the relationship/difference between gene amplification and gene duplication?

gene amplification usually imply multiple copies (more than 2).
gene duplication is only 2 copies.

But that being said, this is however not necessarily true in the case of cancer study where gene duplication is already considered as gene amplification since an extra copy of the gene is usually sufficient to wreak havoc in your cells.

So check the context although it is usually not an issue


> 5) How does the development of tumours support natural selection? Why do cancer cells have better growth advantage?

the growth advantage comes with mutations (that can benefit of cos!).
With accumulated mutations (that can only exist because the cells do not die readily as seen in tumor cells), some of these cells have been altered such that they are better at surviving e.g. use less resources to survive and are able to outcompete others and dominate.
This is natural selection at the molecular scale!