**4. Glycosylation vs. glycation**

Glycosylation and glycation are enzymatic and non-enzymatic reaction respectively, in which glucose and other glucose metabolites show affinity with different biological macromolecules such as proteins, lipids and nucleic acids. Increased presence of glucose both intracellular and extracellular possesses threat to the human and act as risk factor for various metabolic disorders including diabetes mellitus. Both non-enzymatic glycation and enzymatic glycosylation reaction have been shown to play important role in human health. Non-enzymatic glycation leads to the formation of advanced glycation end products (AGEs) that generates as a resultant of protein and lipid glycation with aldose sugars [12, 13]. Prior to the formation of AGEs, the early glycation reaction occurs that form Schiff bases and Amadori products. AGEs formed due to the non-enzymatic glycation generates reactive oxygen species (ROS), that further binds to the particular cell surface receptors and later forms cross link [12, 14].

## **5. SARS-CoV-2 and glycosylation**

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) is severely affecting the worldwide population. SARS-CoV-2 virulence and survival is

*Introductory Chapter: Glimpses of Glycosylation DOI: http://dx.doi.org/10.5772/intechopen.101935*

impacted by the glycans that is covalently linked to the proteins of virus through the process of glycosylation that makes alteration in the virulence of the SARS-CoV-2 virus. It belongs to the coronavirus family which exhibit protein constituted enveloped single-stranded RNA. These viral proteins undergo post-translational modifications (PTMs) that reorganized covalent bonds and modify the polypeptides and in turn modulate the protein functions. Being viral machinery, it uses host cells system to replicate itself and make their copes, their proteins are also subject to PTMs. Glycosylation, palmitoylation of the spike and envelope proteins, phosphorylation, of the nucleocapsid protein are among the major PTMs responsible for the pathogenesis of the viral infection phase. The current knowledge of CoV proteins PTMs is limited and need to be exploring for to understand the viral pathogenesis mechanism and PTMs effect of infection phase.
