Question

Explain the figures below

PAHS PM NO DNA RNA miRNA Retrotransposons Alternative splicing Histone modifications DNA methylation Transposon activation Disease Respiratory Cardiovascular Allergic, immune response

Answer 1

The first figure shows the effect of various substances (air pollutants) on nucleic acids (DNA and RNA) and alteration in nucleic acid processing leads to various kinds of diseases.

We live in an atmosphere which contain different type of pollutants either in the form of gases or solid particle. Continuous exposure to these pollutants leads to hazardous health problems. PAH or polycyclic aromatic compounds are those which are generated through incomplete combustion of organic materials such as coal, wood, petrol, oil. PAH are lipophilic in nature which makes them easily absorbed by the cell membranes. PM or particulate matter are small particles that are formed as a result of the reaction between the pollutants. It includes smoke, liquid droplets, pollens, etc. Along with PAH, PM, nitrogen oxide (NO2), ground-level ozone (O3) which is formed as a result of the reaction between nitrogen oxide and PAH, sulfate (SO4) affects the nucleic acids at different levels such as DNA methylation (exposure lowers the DNA methylation which is on of the key point in gene regulation), alternative splicing, epigenetic mark (miRNA), histone modification, transposon activation, exposure of PAH causes activation of retrotransposons. Alteration in these processes results in altered gene expression and leads to cardiovascular diseases, lung pathologies such as asthma, activated immune cells which lead to inflammation ( oxidative stress induced by these pollutants such as PM, O3 activate the inflammatory pathways) and many more health problems.

The second figure shows the DNA methylation in which nucleotide cytosine is methylated into methylcytosine.

DNA methylation is a very important process. It plays an important role in the regulation of gene expression and is essential for normal development. It regulates the tissue-specific gene regulation, X-chromosome inactivation, aging, carcinogenesis. Methylated DNA is not active DNA means don't express into functional proteins. CpG islands are the region of DNA that contains cytosine (C) and guanine (G) dinucleotide repeats.

The methylation reaction is catalyzed by enzyme DNA methyltransferase (DNMT). The enzyme uses S-adenosyl Methionine (SAM) as a methyl group donor and transfers a methyl group to the 5 position of cytosine. During this reaction, SAM is converted into SAH ( S-adenosyl homocysteine).