Nucleotide Structure and Function Quiz

Study Notes

Nucleotides consist of a nitrogenous base, a pentose monosaccharide, and one to three phosphate groups.
Nitrogenous bases are categorized as purines or pyrimidines.
Pentose monosaccharides are formed from glucose through the hexose phosphate shunt (HMP shunt).

Nucleotides are crucial for all cellular processes.
They serve as building blocks for RNA and DNA.
Nucleotides act as carriers of activated intermediates in the synthesis of carbohydrates, lipids, and conjugated proteins (e.g., UDP-glucose, CDP-choline).
They are structural components of essential coenzymes (e.g., coenzyme A, FAD, NAD+, NADP+).
Some nucleotides act as second messengers in signal transduction pathways (e.g., cAMP, cGMP).
Nucleotides are the cell's "energy currency" (e.g., ATP).
They contribute to the regulation of various metabolic pathways by activating or inhibiting key enzymes.

A pentose sugar added to a base forms a nucleoside.
Ribonucleoside: Contains ribose sugar.
Deoxyribonucleoside: Contains 2-deoxyribose sugar.
Ribonucleosides for A, G, C, and U are: adenosine, guanosine, cytidine, and uridine, respectively.
Deoxyribonucleosides for A, G, C, and T have the prefix "deoxy-" (e.g., deoxyadenosine).
Deoxythymidine is often called thymidine.

One or more phosphate groups attached to a nucleoside form a nucleotide.
The first phosphate group is linked to the 5'-OH of the pentose through an ester linkage.
This forms a nucleoside 5'-phosphate (5'-nucleotide).
The type of pentose is denoted by the prefix: "5'-ribonucleotide" or "5'-deoxyribonucleotide."
One phosphate group forms a nucleoside monophosphate (e.g., AMP).
Two phosphate groups form a nucleoside diphosphate (e.g., ADP).
Three phosphate groups form a nucleoside triphosphate (e.g., ATP).
The second and third phosphate groups are connected by "high-energy" bonds.
Phosphate groups are responsible for the negative charges of nucleotides, leading to DNA and RNA being referred to as "nucleic acids."

Purine synthesis does not occur as a ring but as a nucleotide.
Two pathways contribute to purine synthesis:
- De novo synthesis pathway
- Salvage pathway

The purine ring is constructed from various compounds including amino acids (aspartic acid, glycine, glutamine), CO2, and N10-formyltetrahydrofolate (derived from folic acid, a B vitamin).
The purine ring is primarily assembled in the liver.

PRPP is an activated pentose involved in purine and pyrimidine synthesis and salvage.
PRPP synthetase (ribose phosphate pyrophosphokinase) catalyzes the synthesis of PRPP from ATP and ribose 5-phosphate.
PRPP synthetase is an X-linked enzyme activated by inorganic phosphate.
It is inhibited by purine nucleotides (GMP, AMP, IMP, allopurinol, 6-mercaptopurine): an example of end-product inhibition.