Describe the four biochemical processes that nucleotides participate in. Give examples of nucleotides - other than those containing the nucleotide base adenine- that have a role in each of these processes.

The intricate process of DNA synthesis, also known as DNA replication, is vital for cell growth, replication, and inheritance. Within a cell, nucleotides form the building blocks of DNA, assembling together to create the iconic double helix structure. Each nucleotide in this assembly consists of a sugar, a phosphate group, and a nitrogenous base, either cytosine (C), guanine (G), thymine (T), or adenine (A).

During replication, enzymes called DNA polymerases orchestrate the synthesis, adding deoxyribonucleotide triphosphates (dNTPs) to a growing DNA chain. In this sequence, thymine (instead of uracil found in RNA) pairs with adenine, and cytosine pairs with guanine. This partnership ensures the genetic code is accurately copied for the next generation of cells. The process is semiconservative, meaning that one new and one original strand of DNA form the resulting double helices.

RNA synthesis, commonly referred to as transcription, is a cornerstone of genetic expression. Much like DNA synthesis, transcription relies on nucleotides; however, these are slightly different, known as ribonucleotide triphosphates (NTPs). They contain ribose sugar and one of four nitrogenous bases: adenine (A), cytosine (C), guanine (G), or uracil (U), replacing thymine found in DNA.

RNA polymerase enzymes conduct this transcription process, prying apart the DNA strands and matching RNA nucleotides with the DNA template. Uracil (U) importantly takes the place of thymine (T) in pairing with adenine. This newly formed RNA strand can serve various functions: as messenger RNA (mRNA), transfer RNA (tRNA), or ribosomal RNA (rRNA), each integral to protein synthesis and the gene expression pathway.

Nucleotides are not merely structural pillars of genetic material; they also act as the universal energy currency of the cell. The most known molecule for this role is adenosine triphosphate (ATP), but guanosine triphosphate (GTP) shares the spotlight. These molecules store potential energy within their triphosphate groups; when a cell requires energy, ATP and GTP can release this stored energy by breaking off one phosphate group, transforming into ADP (adenosine diphosphate) or GDP (guanosine diphosphate), respectively.

This energy is the driving force behind countless cellular processes, ranging from protein synthesis to muscle contraction to sending nerve impulses. As such, learning about these nucleotides' roles extends beyond the page, diving into life’s energetically-demanding processes and how they are facilitated at the cellular level.

Lastly, nucleotides play an instrumental role in cell signaling. They can act as secondary messengers, like cyclic guanosine monophosphate (cGMP), allowing cells to communicate and react to diverse stimuli. cGMP, for instance, is crucial for many physiological processes, including regulating the expansion of blood vessels (vasodilation) and processing visual information in the retina.

Constructed using GTP as a precursor, cGMP is synthesized by guanylate cyclase enzymes. The carefully balanced levels of cGMP are imperative for signaling pathways, and disruptions to this balance can have cascading health effects. Thus, the study of this nucleotide underscores the complexity of cellular communication and its impacts on overall organismal function.