Question

Tetrahydrobiopterin A. is synthesized from GTP. B. is an inhibitor of IMP dehydrogenase. C. is synthesized from ATP. D. is a degradation product of guanine. E. requires the addition of glutamine to a purine nucleotide.

Short answer

Answer: Tetrahydrobiopterin is synthesized from GTP.

Step-by-step solution

Eliminate incorrect statements about Tetrahydrobiopterin synthesis

Tetrahydrobiopterin (BH4) is synthesized from GPT and not ATP. Therefore, we can eliminate option C as it states it is synthesized from ATP.

Determine if Tetrahydrobiopterin is an inhibitor of IMP dehydrogenase

IMP dehydrogenase is an essential enzyme in the de novo synthesis of guanine nucleotides. Tetrahydrobiopterin (BH4) is a cofactor involved in the synthesis of neurotransmitters and nitric oxide, but it is not an inhibitor of IMP dehydrogenase. Therefore, we can eliminate option B.

Verify if Tetrahydrobiopterin is a degradation product of guanine

Tetrahydrobiopterin (BH4) is not a degradation product of guanine. It is formed from GTP (Guanosine-5'-triphosphate) through a series of enzymatic reactions. So, option D is incorrect.

Establish if Tetrahydrobiopterin requires the addition of glutamine to a purine nucleotide

Tetrahydrobiopterin (BH4) synthesis doesn't involve the addition of glutamine to a purine nucleotide. Glutamine plays a role in purine synthesis, but it is not directly involved in the formation of Tetrahydrobiopterin. Therefore, we can eliminate option E.

Confirm the correct option

By eliminating all the incorrect options in the previous steps, we are left with option A which states that Tetrahydrobiopterin is synthesized from GTP. This statement is correct, as Tetrahydrobiopterin (BH4) is formed from GTP through a series of enzymatic reactions. So, the correct answer to the exercise is: A. Tetrahydrobiopterin is synthesized from GTP.

Key concepts

GTP

Guanosine-5'-triphosphate (GTP) is one of the fundamental building blocks of nucleic acids and plays a pivotal role in a myriad of cellular processes.
GTP is an energy-rich molecule that shares a similar structure to adenosine triphosphate (ATP), the primary energy currency of the cell. However, GTP has its unique roles that are vital to cellular functions.

Role in Protein Synthesis

GTP is involved in the process of protein synthesis, particularly during the formation of the polypeptide chain in the ribosome. It provides the necessary energy for the binding of the ribosome subunits and the translocation of tRNAs and mRNA.

Signal Transduction

In signal transduction, GTP-binding proteins, often known as G-proteins, use GTP as a source of energy to relay signals from receptors on the cell surface to intracellular effectors.

Synthesis of Tetrahydrobiopterin

Importantly, for our main topic, GTP serves as a precursor in the biosynthesis of tetrahydrobiopterin (BH4). The conversion of GTP to BH4 involves several enzymatic steps, each driving the reaction closer to this crucial coenzyme in neurotransmitter production.

IMP dehydrogenase

IMP dehydrogenase is an enzyme that plays a critical role in the purine nucleotide metabolism, specifically in the synthesis of the guanine nucleotides from inosine monophosphate (IMP).
It catalyzes the oxidation of IMP to xanthosine monophosphate (XMP), a step in the pathway leading to the production of GTP and other guanine-containing nucleotides.

Role in De Novo Purine Synthesis

The de novo synthesis of purine nucleotides is a complex process that initiates with the precursors amino acids, ribose-5-phosphate, CO2, and NH3. IMP is synthesized as the first purine nucleotide and serves as a branch point that leads to the generation of either adenine or guanine nucleotides.

IMP Dehydrogenase Inhibition

Because of its central role, IMP dehydrogenase is a target for certain immunosuppressive and antiviral drugs, which inhibit the enzyme to decrease the proliferation of certain cells or viruses. However, tetrahydrobiopterin does not inhibit this enzyme, as clarified in the exercise.

Purine Nucleotide Metabolism

Purine nucleotide metabolism encompasses the pathways by which purine bases, which are crucial components of DNA and RNA, are synthesized and recycled within the cell.
Purine nucleotides, the building blocks of genetic material, are required not only for replication and transcription but also for energy transfer, cellular signaling, and enzyme regulation.

De Novo Synthesis Pathway

Cells can create purine nucleotides from scratch through the de novo synthesis pathway. This pathway starts with small molecules like amino acids and proceeds through multiple reactions to form IMP, which subsequently leads to the production of AMP (adenosine monophosphate) and GMP (guanosine monophosphate).

Salvage Pathway

Alternatively, the salvage pathway allows cells to recycle free purine bases by reattaching them to ribose-5-phosphate to form purine nucleotides. This energy-conserving process is essential for maintaining an adequate supply of nucleotides for the cell's needs.

Connection with BH4 Synthesis

In the context of our exercise, GTP, a purine nucleotide, is the substrate for the synthesis of tetrahydrobiopterin (BH4), highlighting the interconnection between purine nucleotide metabolism and the biosynthesis of other critical biomolecules.