pyrimidine nucleoside metabolic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways involving any pyrimidine nucleoside, one of a family of organic molecules consisting of a pyrimidine base covalently bonded to ribose (a ribonucleoside) or deoxyribose (a deoxyribonucleoside). [GOC:jl, ISBN:0140512713]

Pyrimidine nucleoside metabolic process is a fundamental biological pathway responsible for the synthesis, utilization, and degradation of pyrimidine nucleosides. These molecules, composed of a pyrimidine base (cytosine, uracil, or thymine) linked to a ribose or deoxyribose sugar, are essential building blocks for DNA and RNA, the genetic material of all living organisms.

**1. De Novo Synthesis:** The de novo pathway is the primary route for synthesizing pyrimidine nucleotides. It begins with the condensation of aspartate and carbamoyl phosphate to form carbamoylaspartate, followed by a series of enzymatic steps involving dihydroorotate dehydrogenase, orotate phosphoribosyltransferase, and orotidine 5'-phosphate decarboxylase. These reactions ultimately lead to the formation of UMP (uridine monophosphate), the precursor of other pyrimidine nucleotides.

**2. Salvage Pathway:** The salvage pathway provides an alternative route for generating pyrimidine nucleotides by recycling pre-existing bases or nucleosides. This pathway relies on enzymes like uridine phosphorylase and thymidine kinase, which convert uracil and thymine into their respective monophosphates.

**3. Nucleotide Interconversion:** Pyrimidine nucleotides can be interconverted through a series of enzymatic reactions. For instance, UMP can be converted to CMP (cytidine monophosphate) by CTP synthetase.

**4. Degradation:** The breakdown of pyrimidine nucleotides occurs primarily in the liver. Enzymes like uracil-DNA glycosylase and thymine-DNA glycosylase remove damaged or modified pyrimidine bases from DNA. Further degradation leads to the formation of β-alanine, β-aminoisobutyrate, and ammonia.

**5. Regulation:** The synthesis and degradation of pyrimidine nucleotides are tightly regulated to maintain cellular homeostasis. Feedback mechanisms and allosteric regulation ensure that nucleotide levels are adequate for DNA replication and RNA transcription, but not excessive, preventing potential cytotoxic effects.

**6. Clinical Significance:** Dysregulation of pyrimidine nucleoside metabolism can lead to a range of human diseases. Deficiencies in enzymes involved in the pathway can cause genetic disorders like orotic aciduria and Lesch-Nyhan syndrome. Conversely, aberrant nucleotide metabolism can contribute to the development of cancers, autoimmune diseases, and other conditions.

Overall, the pyrimidine nucleoside metabolic process is a complex and tightly regulated pathway essential for maintaining cellular function and survival. Its intricate mechanisms and diverse roles highlight its importance in various biological processes and its relevance to human health.'
"

Proteins (2)

Compounds (25)