1. Introduction
  1.1 Background and significance
  1.2 Objectives of the study
2. Protein Ubiquitination: An Overview
  2.1 Definition and general principles
  2.2 Types of ubiquitin modifications
  2.3 Biological functions of protein ubiquitination
3. Mechanisms of Protein Ubiquitination
  3.1 E1, E2, and E3 enzymes: The ubiquitin conjugation machinery
  3.2 Substrate recognition and specificity
  3.3 Linkage types and polyubiquitin chain assembly
4. Deubiquitination: Reversal of Ubiquitin Modifications
  4.1 Deubiquitinases (DUBs): Classification and functions
  4.2 Regulation of protein stability by DUBs
5. Functional Consequences of Protein Ubiquitination
  5.1 Protein degradation by the proteasome
  5.2 Ubiquitin-mediated endocytosis and protein trafficking
  5.3 Signaling pathways regulated by protein ubiquitination