Biochemistry: Ribose 5-Phosphate Formation

Questions and Answers

What is the primary role of glutathione in red blood cells?

It enhances hemoglobin synthesis.

It maintains the reduced state of sulfhydryl groups of proteins. (correct)

It aids in the production of ATP.

It promotes the oxidation of lipids.

Which form of G6PD deficiency is characterized by normal enzyme stability but low activity levels?

Chronic Nonspherocytic Anemia

G6PD Mediterranean (correct)

Class III Deficiency

Class I Deficiency

What is the outcome of the oxidation of sulfhydryl groups in proteins?

Protein denaturation and formation of Heinz bodies. (correct)

Enhanced cell membrane integrity.

Increased enzyme activity.

Improved red blood cell lifespan.

What happens to G6PD enzyme activity in the oldest red blood cells?

It decreases to the lowest level. Signup and view all the answers

Which factors can compromise the glutathione defense system in G6PD deficiency?

Presence of infections and certain drugs. Signup and view all the answers

What role does NADPH oxidase play in the immune response?

It converts molecular O2 to superoxide in phagocytic cells. Signup and view all the answers

Which components are present in the subunits of NADPH oxidase?

Cytochrome and flavin coenzymes Signup and view all the answers

What is one consequence of a genetic deficiency in NADPH oxidase?

Severe, persistent chronic pyogenic infections Signup and view all the answers

How is NADPH oxidase activated in the immune response?

Recognition by phagocyte receptors Signup and view all the answers

What type of infections are typically associated with Chronic Granulomatosis?

Chronic pyogenic infections Signup and view all the answers

During the respiratory burst, what is formed from the transfer of electrons via NADPH?

Superoxide Signup and view all the answers

What is a major result of phagocytosis by immune cells?

Internalization of microorganisms Signup and view all the answers

Which factor regulates the activity of NADPH oxidase?

Hormonal signals Signup and view all the answers

What does the formation of granulomas typically indicate in immune response?

Sequestration of bacteria that were not destroyed Signup and view all the answers

Which of the following is a correct sequence of events involving NADPH oxidase?

Phagocytosis > NADPH oxidase activation > Reactive oxygen species generation Signup and view all the answers

Which enzyme is responsible for transferring a 3-carbon unit from sedoheptulose 5-phosphate to G3P?

Transaldolase Signup and view all the answers

What is the primary role of ribose 5-phosphate in cellular processes?

Nucleotide and nucleic acid synthesis Signup and view all the answers

Which compound is produced alongside NADPH through the conversion of glucose 6-phosphate?

Fructose-6-phosphate Signup and view all the answers

Which of the following reactions does NOT involve the enzyme transketolase?

Formation of ribose 5-phosphate from G3P Signup and view all the answers

What is the stoichiometric outcome of the pentose phosphate pathway starting from glucose 6-phosphate?

3 G6P + 6 NADP+ → 6 NADPH + 2 F6P + 3 CO2 Signup and view all the answers

In a situation where there is a high demand for NADPH, which pathway is likely to be favored?

Pentose phosphate pathway Signup and view all the answers

What essential element is required by Glutathione Peroxidase for its function?

Selenium Signup and view all the answers

Which of the following statements is false regarding erythrose 4-phosphate?

It requires a cofactor for its metabolism. Signup and view all the answers

Which of the following best describes the role of glutathione in detoxifying H2O2?

Reduces it to form water and oxidized glutathione Signup and view all the answers

What is a significant difference between transaldolase and transketolase in the pentose phosphate pathway?

Transaldolase transfers 3-carbon units, while transketolase transfers 2-carbon units. Signup and view all the answers

Which substrate is formed from the combination of xylulose 5-phosphate and erythrose 4-phosphate?

F6P Signup and view all the answers

What is the chemical composition of reduced glutathione?

ϒ-glutamylcysteinylglycine Signup and view all the answers

Which reactive oxygen species is formed from the partial reduction of molecular O2?

Superoxide Signup and view all the answers

What process regenerates reduced glutathione after it has been oxidized?

Utilization of NADPH via glutathione reductase Signup and view all the answers

What type of reaction does Glutathione Peroxidase primarily carry out?

Reduction of H2O2 Signup and view all the answers

What is the product of oxidized glutathione undergoing reaction with other thiol groups?

Disulfides Signup and view all the answers

Which of the following radicals is least likely to form during the partial reduction of O2?

Nitroxyl radical Signup and view all the answers

What structural feature of reduced glutathione allows it to fulfill its function as an antioxidant?

Sulfhydryl group Signup and view all the answers

What is the main method by which glutathione detoxifies reactive oxygen species?

Reduction reactions Signup and view all the answers

What is a consequence of decreased G6PD activity in red blood cells?

Increased formation of oxidative stress Signup and view all the answers

Which of the following mutations would most likely show an alteration in kinetic properties?

Mutations causing decreased catalytic activity Signup and view all the answers

How does hemolysis correlate with G6PD activity in patients?

It directly correlates with residual enzyme activity Signup and view all the answers

What effect does impaired NADPH formation have on red blood cells?

Decreases resistance to oxidative stress Signup and view all the answers

What is a result of increased resistance to Falciparum malaria linked to G6PD mutations?

Improved ability to manage red blood cell longevity Signup and view all the answers

Which factor does NOT affect the severity of the disease connected to G6PD deficiency?

Patient's age at diagnosis Signup and view all the answers

What structural aspect of an enzyme's active site is indicated in the content?

It's rarely affected by mutations Signup and view all the answers

Which of the following describes the impact of decreased stability of red blood cells due to G6PD mutations?

Increased hemolytic episodes Signup and view all the answers

Which biochemical factor is primarily affected by decreased G6PD activity?

NADPH formation Signup and view all the answers

How does the failure to maintain adequate reduced glutathione levels impact red blood cells?

Increases free radical accumulation Signup and view all the answers

Study Notes

Formation of Ribose 5-Phosphate

Ribose 5-phosphate synthesizes from the transfer of a 3-carbon unit from sedoheptulose 5-phosphate to glyceraldehyde 3-phosphate (G3P).
Key intermediates include fructose-6-phosphate and erythrose-4-phosphate.
Enzyme involved: transaldolase, which does not require cofactors.
Xylulose 5-phosphate and erythrose 4-phosphate are converted to fructose 6-phosphate (F6P) and G3P using TPP-dependent transketolase.

Summary of Reactions

Stoichiometry: 3 G6P + 6 NADP+ → 2 F6P + 3 CO2 + G3P + 6 NADPH + 6 H+.

Regulation of the Pathway

Glutathione Peroxidase:
- A selenium-requiring enzyme that reduces hydrogen peroxide (H2O2) to detoxify it.
- Reduces oxidized glutathione (GSSG) back to reduced glutathione (GSH) using NADPH.

Formation of Reactive Intermediates

Molecular oxygen, when partially reduced, creates reactive oxygen species such as superoxide and hydrogen peroxide.
Immune response:
- Bacteria are recognized by immune cells leading to phagocytosis and oxidation of O2 to superoxide via NADPH oxidase in white blood cells.

Genetic Deficiencies of NADPH Oxidase

Chronic Granulomatosis:
- A severe condition leading to persistent infections and granuloma formation.
- Complications from chronic hemolysis can decrease life span.
- Some mutations do not affect enzyme structure but change kinetic properties.

Role of G6PD in RBCs

Reduced G6PD activity results in impaired NADPH formation.
Insufficient reduced glutathione increases oxidative stress sensitivity, leading to red blood cell instability and hemolysis.
G6PD variants influence the severity of the condition, with class III (G6PD A-) showing moderate deficiencies in reticulocytes but not old RBCs.

Variants of G6PD Deficiency

G6PD Mediterranean:
- Class II deficiency with normal enzyme stability but very low activity.
Class I mutations can cause Chronic Nonspherocytic Anemia.

Hemolysis Mechanisms

Integrity of red blood cells requires ATP, NADH, and NADPH from the pentose phosphate pathway (PPP).
Compromised glutathione defense systems due to G6PD deficiency are particularly vulnerable to infections, drugs, and dietary factors like fava beans.

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Description

This quiz covers the formation of Ribose 5-Phosphate, focusing on the transfer of 3-carbon units from sedoheptulose 5-phosphate to G3P. It also examines key intermediates of glycolysis such as fructose-6-phosphate and erythrose-4-phosphate, as well as the role of the enzyme transaldolase in this process.