Question

describe how chromatin can be used to limit the transcription of genes. include the differences between euchromatin, and heterochromatin, and how the two types of chromatin can be interchanged.

Answer 1

The state of chromatin can limit access of transcription factors and RNA polymerase to DNA promoters, contributing to the restrictive ground state of gene expression. In order for gene transcription to occur, the chromatin structure must be unwound. Chromatin structure contributes to the varying levels of complexity in gene regulation. It allows simultaneous regulation of functionally or structurally related genes that tend to be present in widely spaced clusters or domains on eukaryotic DNA. Interactions of chromatin with activators and repressors can result in domains of chromatin that are open, closed, or poised for activation. Chromatin domains have various sizes and different extents of stability. These variations allow for phenomena found solely in eukaryotes, such as transcription at various stages of development and epigenetic memory throughout cell division cycles. They also allow for the maintenance of differentiated cellular states, which is crucial to the survival of the multicellular organism.

the main difference between euchromatin and heterochromatin

definition of heterochromatin: The area of the chromosomes which are intensely stained with DNA-specific strains and are relatively condensed is known as heterochromatin. They are the tightly packed form of DNA in the nucleus.

definition of euchromatin: That part of chromosomes, which are rich in gene concentrations and are a loosely packed form of chromatin is called euchromatin. They are active during transcription.

BASIS FOR COMPARISON	HETEROCHROMATIN	EUCHROMATIN
Meaning	The tightly packed form of DNA in the chromosome is called as heterochromatin.	The loosely packed form of DNA in the chromosome is called as euchromatin.
DNA density	High DNA density.	Low DNA density.
Kind of stain	Stained dark.	Lightly stained.
Where they are present	These are found at the periphery of the nucleus in eukaryotic cells only.	These are found in the inner body of the nucleus of prokaryotic as well as in eukaryotic cells.
Transcriptional activity	They show little or no transcriptional activity.	They actively participate in the process of transcription.
Other features	They are compactly coiled.	They are loosely coiled.
They are late replicative.	They are early replicative.
Regions of heterochromatin are sticky.	Regions of euchromatin are non-sticky.
Genetically inactive.	Genetically active.
Phenotype remains unchanged of an organism.	Variation may be seen, due to the affect in DNA during the genetic process.
It permits the gene expression regulation and also maintains the structural integrity of the cell.	It results in genetic variations and permits the genetic transcription.

interchange of euchromatin and hetreochromatin

The changing in expression based on density of segments of chromosomes is the basis for the field of epigenetics. The mechanisms of chromatin density change are:

1. DNA methylation- can cause segments of DNA to become more densely packed and downregulate expression, which is an example of euchromatin changing to heterochromatin.

2. Histone acetylation- can cause segments of DNA to become less densely packed and upregulate expression, which is an example of heterochromatin changing to euchromatin.

Both these events occur as a zygote develops into a fetus.