nucleoside metabolic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways involving a nucleoside, a nucleobase linked to either beta-D-ribofuranose (a ribonucleoside) or 2-deoxy-beta-D-ribofuranose, (a deoxyribonucleoside), e.g. adenosine, guanosine, inosine, cytidine, uridine and deoxyadenosine, deoxyguanosine, deoxycytidine and thymidine (= deoxythymidine). [GOC:ma]

Nucleoside metabolic process is a fundamental biological process encompassing the synthesis, breakdown, and interconversion of nucleosides, which are the building blocks of nucleic acids (DNA and RNA). This complex process involves a series of enzymatic reactions that play crucial roles in numerous cellular functions, including DNA replication, RNA transcription, and energy production.

**Synthesis:**
- **De novo synthesis:** Nucleosides can be synthesized from simple precursors like amino acids, ribose-5-phosphate, and tetrahydrofolate. This pathway involves multiple steps, starting with the formation of purine and pyrimidine bases, followed by their attachment to a ribose sugar molecule.
- **Salvage pathways:** Nucleosides can also be recovered and recycled from existing nucleotides or nucleic acids through salvage pathways. These pathways utilize enzymes like nucleoside kinases to phosphorylate nucleosides to form nucleoside monophosphates, which can then be used in the biosynthesis of nucleotides.

**Breakdown:**
- **Nucleosidase activity:** Nucleosides can be broken down into their constituent parts: a purine or pyrimidine base and a ribose or deoxyribose sugar. This step is catalyzed by enzymes known as nucleosidases.
- **Phosphorylase activity:** Alternatively, nucleosides can be cleaved by phosphorylases, yielding a phosphate group and a base.
- **Degradation of bases:** The resulting purine and pyrimidine bases can be further degraded into simpler molecules, which can be used as precursors for other biosynthetic pathways or excreted from the body.

**Interconversion:**
- **Ribonucleosides to deoxyribonucleosides:** Ribonucleosides, the building blocks of RNA, can be converted to deoxyribonucleosides, the building blocks of DNA, through a series of enzymatic reactions involving ribonucleotide reductase.
- **Base modifications:** Some nucleosides can undergo modifications to their bases, leading to the formation of different nucleosides with altered properties.

**Regulation:**
- Nucleoside metabolism is tightly regulated to ensure the proper balance of nucleotide precursors for DNA replication, RNA transcription, and other cellular processes.
- Regulation occurs at multiple levels, including enzyme expression, feedback inhibition, and allosteric regulation.

**Clinical significance:**
- Defects in nucleoside metabolism can lead to a variety of genetic disorders, including Lesch-Nyhan syndrome, adenosine deaminase deficiency, and severe combined immunodeficiency.
- Drugs targeting nucleoside metabolism are used to treat various diseases, including cancer, viral infections, and autoimmune diseases.

**Conclusion:**
Nucleoside metabolic process is an essential pathway for life, playing a vital role in DNA replication, RNA transcription, and cellular energy production. Understanding this process is crucial for developing new therapies for a range of diseases.'
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