what exactly is gene expression, and what does it have to do with the structural organization of chromatin?

Answer 1

Gene expression is also known as transformation. This is when an organism starts to show that it has the characteristics of the gene. The theory of gene expression is widely used in genetic engineering, for example, if the scientist wants to make the maize plant pesticide resistant, what he can do is to insert the pesticide resistant gene into the plant, so that the plant will become pesticide resistant.


Perhaps the most likely way we can relate gene expression to the structural organization of chromatin is to go into DNA condensation.

By now, you would have probably known that genes are segments of DNA. These DNA contain the necessary genetic information for an organism to be what it is.

DNA condensation only occurs when the cell undergoes division. It becomes thicker as it needs to protect the fragile and small DNA.

Firstly, it twists around proteins (histones) 2½ times to form chromatin

Open chromatin- can replicate


Then, it twists some more into Chromatin Fibers, a basic organizational unit of eukaryotic chromosomes

Active Euchromatin- can replicate


After that, it intertwines to form an inactive euchromatin or closed chromatin

This means that DNA can no longer replicate, or be read by mRNAs -> inactive


It then condenses into inactive heterochromatin

Finally, it forms the entire mitotic chromosome


The chromosome doubles and then divides. It will revert back to the DNA after the cell has completed division. That way, both cells will now have the same DNA/gene. They will thus have the same characteristics.

Answer 2

Gene expression refers to the whole process that leads to the formation of the final gene product.
Usually this means transcription of DNA to RNA and translation of RNA to protein. In the more generalized concept of the "gene" it also means the transcription of DNA to other forms of RNA which don't encode proteins, like ribosomal and transfer RNA.

In order for transcription to occur the RNA polymerase must have access to the specific site on the DNA. When DNA is too compact like in the case of heterochromatin this is not possible.
When DNA is less compact, then the polymerase and factors activating gene expression can act on DNA. The effect of the polymerase and transcription factors is a further loosening of the structure in that area since the action of these molecules disrupts the histone-DNA interactions. In fact some transcription activators bind to a stretch of DNA that is not bound by histones and displace downstream nucleasomes so that the polymerase and other transcritpion factors can bind.
Also it is quite obvious that there are issues of stereochemical hinderance-the bulky polymerase molecule needs quite some space to act and thus displaces the histones of the nucleosome (in a specific manner) in order to transcribe.

Answer 3

there are two types of chromatin euchromatin and heterochromatin, euchromatin is the chromatin containing the genes that will express, this is DNA packed around histones, etc.. this chromatin is the one with active transcription and so translation... heterochromatin is a chromatin that is not in active transcription, euchromatin is usually transformed in heterochromatin so that some genes do not transcribe, heterochromatin is a way of protecting genes while they are not in use...
gene expression is the transcription and translation of it...