Purine and Pyrimidine Biology Quiz

Study Notes

Purine and pyrimidine are nitrogenous bases that make up the two different kinds of nucleotide bases in DNA and RNA.
The two-carbon nitrogen ring bases are purines (adenine and guanine), while the one-carbon nitrogen ring bases are pyrimidines (thymine and cytosine).
Both purines and pyrimidines serve as a form of energy for cells, and are essential for production of DNA and RNA, proteins, starch, regulation of enzymes, and cell signaling.

Nucleotides are building blocks of nucleic acids (DNA and RNA).
A nucleic acid contains a chain of nucleotides linked together with covalent bonds to form a sugar-phosphate backbone with protruding nitrogenous bases.
The two chains in the double helix are held together along their length by hydrogen bonds that form between the bases on one chain and the bases on the other.

One of the important specialized pathways of a number of amino acids is the synthesis of purine and pyrimidine nucleotides.
These nucleotides are important for a number of reasons, including being sources of energy that drive most of our reactions.
ATP, GTP, UTP, and CTP are nucleotides used in various cellular processes, such as protein synthesis, glucose activation, and lipid metabolism.

Gout is a disease characterized by an increased urate in the body, leading to urate deposits in joints.
Humans lack uricase, which is why their uric acid levels are higher.
In the kidney, urate is filtered at the glomerulus and fully reabsorbed in the proximal tubule.
Gout is classified as primary or secondary, depending on the cause of increased urate levels.

Primary gout is caused by:
- Defects in synthesis or excretion of urate, often due to an enzyme called PRPP.
- Hereditary or genetic conditions, such as glucose-6-phosphatase deficiency.
Secondary gout is caused by:
- Increased production of urate or impaired excretion of urate as a result of other diseases.
- Increased turnover from increased cell breakdown in diseases such as polycythemia, leukemia, pernicious anemia, chronic hemolytic anemia, and lymphosarcoma.

Pyrimidines undergo ring cleavage, and the usual end products of catabolism are beta-amino acids, plus ammonia and carbon dioxide.
Pyrimidines from nucleic acids or the energy pool are acted upon by nucleotidases and pyrimidine nucleoside phosphorylase to yield the free bases.
The 4-amino group of both cytosine and 5-methyl cytosine is released as ammonia, which is a toxic product of nitrogen metabolism.
The urea cycle or ornithine cycle converts excess ammonia into urea in the mitochondria of liver cells, which is then excreted in the urine.