Reply to Bio Bulletin 1

For the question posted.
I enjoyed reading the suggested answer posted in comments. Sounds like a physio student talking with so many factors considered (which is good) but allow me to sum it up =)

Before we talked about transcriptional control, let's look at the natural state of the chromatin.
1) DNA methylation.

For quite a handful of eukaryotes (not all), there is observed DNA methylation near certain genes and it is believed to be associated with the expression of tissue-specific genes with methylation inhibiting the TF and RNA polymerase from initiating transcription. Thus if you imagine a clone of stem cells, when some start to differentiate, the DNA of these differentiated cells might be methylated at certain parts so that certain genese are prevented from expressing. And this methylation is inheritable. Makes sense?

2) decondensation/condensation of chromatin.
So some genes are a no-go. but what about those that can work/
we know that DNA is wound up with histones forming nucleosomes and then 30nm fibre. But you would also know that gene transcription can only take place if the chromatin decondense (greater than 30nm) to allow for the access of TF and RNA polymerase. In this aspect, there are many proposed mechanisms. The reader talked about histone methylation....I need to check that. The histones can be modified in many ways and while methlyation is one of them, I am not 1oo% clear on their effect but I can tell you that the most regarded one is acetylation of the histone's cysteine residues, making it negative. So let you to go and imagine why this -ve charge is important in decondensation k?

Cool yah? =P =)