Final answer:
In biology, histone proteins H3-H4 and H2A-H2B are added to DNA with the assistance of histone chaperones and facilitated by enzymes like histone-lysine N-methyltransferases. The direct answer 'removal of nucleosomes from the DNA' is not entirely correct, as it pertains to chromatin remodeling rather than histone assembly. Histone chaperones and modifying enzymes like DNA ligase during DNA repair are more relevant to this process.
Step-by-step explanation:
Chromatin structure is dynamically modified by histone proteins such as H3-H4 and H2A-H2B, which are added to DNA through the process involving several enzymatic activities. These enzymes help in the packaging and regulation of the DNA within the nucleus. Among the multiple options given, the correct direct answer to what aids in adding these histones to DNA is 'b. the removal of nucleosomes from the DNA,' which is part of chromatin remodeling. However, this is not the complete story, as nucleosome removal would rather be a step toward making the DNA accessible for events like transcription, and is not directly related to the assembly of histones onto DNA.
The nucleosome assembly process necessitates the presence of assembly factors like histone chaperones, which escort and guide the deposition of H3-H4 dimers and H2A-H2B dimers onto DNA to form nucleosomes. Additionally, specific enzymes like histone-lysine N-methyltransferase EZ1 and EZ2 can modify histones by adding methyl groups, impacting their interaction with the DNA and other histones. A more related answer to the addition of histones would also include the action of DNA ligase in the DNA repair process, which can seal phosphodiester bonds forming the backbone of DNA during the addition of nucleotides.