Final answer:
The two types of CpG sites are methylated and unmethylated, found in CpG islands near gene promoters, affecting gene expression and DNA-protein interactions.
Step-by-step explanation:
The two types of CpG sites are methylated CpG sites and unmethylated CpG sites. CpG sites are located in CpG islands, which are regions of DNA with a high frequency of CG dinucleotides, typically found near gene promoters. In methylated CpG sites, a methyl group is added to the cytosine, which affects gene expression by altering the way DNA interacts with proteins, especially histones. In contrast, unmethylated CpG sites do not have this methyl group, allowing the DNA to be more accessible for transcription and other processes.
Within the DNA molecule, each nucleotide contains a deoxyribose sugar, a phosphate group, and a nitrogenous base. The bases cytosine and guanine (forming the CG pair) participate in complementary base pairing with three hydrogen bonds stabilizing this interaction. The specific sequence of bases, including cytosine and guanine, encodes the genetic information.