Chromatin structure and role of chemical modifications of dna and histones, as the first "on" switch for turning on eukaryotic gene expression. define the term epigenetics.

The chromatin structure undergoes various modification for proper gene expression. Histone acetylation, histone deacetylation, methylation and sumoylation are important for the epigenetics.

Epigenetics may be defined as the change in the genome that affect gene activity, its expression and heritable phenotypic change of the organisms. The DNA sequence is not altered in the epigenetic modification but the gene expression has been modified by methylation or acetylation.

eukarya because is is like alche and b is bacteria and d is animals

explanation:

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.