Questions and Answers
What is the primary function of thymidylate synthase in nucleotide metabolism?
Which substance inhibits the enzyme carbamoyl phosphate synthetase II (CPS II)?
What is one of the consequences of adenosine deaminase (ADA) deficiency?
Which compounds serve as the primary donors of nitrogen in the synthesis of the pyrimidine ring?
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What is a product of pyrimidine degradation that is highly soluble?
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Which of the following statements accurately describes a component of a nucleotide?
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What distinguishes thymine from uracil in their structure?
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Which pathway is critical for the metabolism of purines and directly leads to the production of uric acid?
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Deficiency in which enzyme leads to disorders associated with severe combined immunodeficiency (SCID)?
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Which of the following pathways contributes to the synthesis of pyrimidine bases?
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Study Notes
Lactic Acidosis and Environmental Exposure
- Lactic acidosis can be influenced by environmental factors such as drug use and lead exposure.
Adenosine Deaminase (ADA) Deficiency
- ADA deficiency leads to adenosine accumulation, converted to ribonucleotide or deoxyribonucleotide forms by kinases.
- Elevated dATP inhibits ribonucleotide reductase, hindering deoxyribose nucleotide synthesis.
- Inability to synthesize DNA can result in developmental arrest and apoptosis.
- Severe forms cause severe combined immunodeficiency (SCID), reducing T cells, B cells, and natural killer cells.
Pyrimidine Synthesis and Degradation
- Pyrimidine ring forms before attachment to ribose 5-phosphate from PRPP.
- Ring atoms derived from glutamine, CO2, and aspartate.
- First three enzymes in the pathway are functional domains of the single polypeptide CAD.
- Key steps include:
- Step 1: Carbamoyl phosphate synthesis from glutamine and CO2, regulated by CPS II, inhibited by uridine triphosphate (UTP), activated by PRPP.
- Step 2: Carbamoyl aspartate formation by aspartate transcarbamoylase.
- Step 3: Dihydroorotate formed by the closure of the pyrimidine ring.
Uric Acid Production
- Both GMP and AMP contribute to uric acid production, essential for purine metabolism.
- ADA deficiency may contribute to SCID, affecting uric acid levels.
Nucleotide Composition
- A nucleotide consists of a pentose monosaccharide, a nitrogenous base, and phosphate group/s.
Synthesis Pathways for Purine and Pyrimidine Bases
- Two main synthesis pathways:
- De novo synthesis: Involves constructing bases from simple precursors.
- Salvage pathways: Assembling bases from recycled pre-existing purines and pyrimidines.
Inosine Monophosphate (IMP) Synthesis
- Synthesis of IMP involves multiple steps, serving as a precursor to AMP and GMP.
- Four steps necessitate ATP, while two require N10-formyl-THF.
AMP and GMP Synthesis
- IMP conversion to AMP or GMP occurs in two steps, each inhibited by the respective end product.
- AMP synthesis utilizes GTP as an energy source and aspartate as a nitrogen source.
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Description
This quiz explores the concepts of lactic acidosis and its relation to environmental exposures, particularly drug use and lead exposure. It also covers the enzymatic conversion of dUMP to dTMP through thymidylate synthase, highlighting the role of N5,N10-methylene-THF in the synthesis process.
