Podcast
Questions and Answers
What is the main function of nitric oxide (NO) in the body?
What is the main function of nitric oxide (NO) in the body?
Which enzyme is primarily responsible for the synthesis of nitric oxide?
Which enzyme is primarily responsible for the synthesis of nitric oxide?
What characterizes chronic granulomatous disease?
What characterizes chronic granulomatous disease?
What is the primary consequence of glucose 6-phosphate dehydrogenase (G6PD) deficiency?
What is the primary consequence of glucose 6-phosphate dehydrogenase (G6PD) deficiency?
Signup and view all the answers
Which of the following describes an O2-independent mechanism used by neutrophils and monocytes to destroy pathogens?
Which of the following describes an O2-independent mechanism used by neutrophils and monocytes to destroy pathogens?
Signup and view all the answers
What are NADPH's primary roles in biochemistry?
What are NADPH's primary roles in biochemistry?
Signup and view all the answers
Which of the following processes does NOT utilize NADPH?
Which of the following processes does NOT utilize NADPH?
Signup and view all the answers
Which statement about reactive oxygen species (ROS) is true?
Which statement about reactive oxygen species (ROS) is true?
Signup and view all the answers
Which enzyme is important for reducing hydrogen peroxide in the presence of NADPH?
Which enzyme is important for reducing hydrogen peroxide in the presence of NADPH?
Signup and view all the answers
What is the main function of the Cytochrome P450 monooxygenase system?
What is the main function of the Cytochrome P450 monooxygenase system?
Signup and view all the answers
What is a consequence of a low level of antioxidants in cells?
What is a consequence of a low level of antioxidants in cells?
Signup and view all the answers
Which molecule is primarily generated during the Panose Phosphate Pathway (PPP) and is essential for red blood cells?
Which molecule is primarily generated during the Panose Phosphate Pathway (PPP) and is essential for red blood cells?
Signup and view all the answers
Which type of reactions primarily depends on NADPH as an electron donor?
Which type of reactions primarily depends on NADPH as an electron donor?
Signup and view all the answers
What is the primary purpose of the pentose phosphate pathway?
What is the primary purpose of the pentose phosphate pathway?
Signup and view all the answers
Where does the pentose phosphate pathway occur within the cell?
Where does the pentose phosphate pathway occur within the cell?
Signup and view all the answers
Which enzyme initiates the rate-limiting reaction of the oxidative branch of the pentose phosphate pathway?
Which enzyme initiates the rate-limiting reaction of the oxidative branch of the pentose phosphate pathway?
Signup and view all the answers
What type of reactions occur in the reversible non-oxidative branch?
What type of reactions occur in the reversible non-oxidative branch?
Signup and view all the answers
What is required by transketolases for their enzymatic activity?
What is required by transketolases for their enzymatic activity?
Signup and view all the answers
In which cell types is the pentose phosphate pathway particularly active in biosynthesis of fatty acids and steroid hormones?
In which cell types is the pentose phosphate pathway particularly active in biosynthesis of fatty acids and steroid hormones?
Signup and view all the answers
What happens when a cell needs ribose 5-phosphate more than NADPH?
What happens when a cell needs ribose 5-phosphate more than NADPH?
Signup and view all the answers
Which of the following correctly describes a product of the oxidative reactions in the pentose phosphate pathway?
Which of the following correctly describes a product of the oxidative reactions in the pentose phosphate pathway?
Signup and view all the answers
Study Notes
Pentose Phosphate Pathway
- Also known as the hexose monophosphate shunt (HMP shunt)
- A metabolic pathway that is a bypass around the first stage of glycolysis.
- Occurs in the cytosol of all cells.
Functions
- Produces reducing power in the form of NADPH.
- Generates ribose 5-phosphate for nucleotide synthesis.
Overview
- Involves 2 irreversible oxidative reactions, followed by reversible sugar-phosphate interconversions.
- Has 2 branches: an irreversible oxidative branch and a reversible non-oxidative branch.
3 Reactions
-
1. Dehydration of glucose 6-phosphate to 6-phosphogluconolactone: This reaction is catalyzed by glucose 6-phosphate dehydrogenase (G6PD), using NADP+ as a coenzyme. NADPH is a potent inhibitor of G6PD, and insulin upregulates G6PD gene expression.
-
2. Formation of ribulose 5-phosphate: 6-phosphogluconolactone is hydrolyzed to 6-phosphogluconate, which then undergoes oxidative decarboxylation to produce ribulose 5-phosphate. This reaction is facilitated by 6-phosphogluconate dehydrogenase.
-
(Additional information on specific enzymes and the overall reaction process is found on page 4 of the document).
Main Advantages
- Liver, mammary glands, and adipose tissue: active in NADPH-dependent fatty acid biosynthesis.
- Testes, ovaries, placenta, and adrenal cortex: active in NADPH-dependent steroid hormone biosynthesis.
- Red blood cells: rely on NADPH to maintain reduced glutathione, critical for cellular redox balance.
Reversible Non-oxidative Reactions
- Occurs in cells synthesizing nucleotides and nucleic acids.
- Catalyzes the interconversion of sugars containing 3-7 carbons.
- Enables the conversion of ribulose 5-phosphate into ribose 5-phosphate (for nucleotide synthesis) or glycolysis intermediates (fructose 6-phosphate and glyceraldehyde 3-phosphate).
Main Enzymes
- The primary enzymes involved in non-oxidative reactions are transaldolase and transketolases.
- Thiamine pyrophosphate (TPP) is crucial for the function of these enzymes, as well as pyruvate dehydrogenase (PDH) and α-ketoglutarate dehydrogenase (aKGDH).
Cell Needs and NADPH/R5P
- If the cell requires NADPH but not ribose 5-phosphate, ribulose 5-phosphate is converted into glyceraldehyde 3-phosphate and fructose 6-phosphate, which then enter glycolysis.
- When the cell needs more ribose 5-phosphate than NADPH, fructose 6-phosphate and glyceraldehyde 3-phosphate are converted into ribose 5-phosphate.
Most Important Products
- NADPH: essential for various reductive biosynthetic processes, including fatty acid synthesis.
- Ribose 5-phosphate: used for the synthesis of RNA, DNA, NAD+, FAD, ATP, and coenzyme A.
Uses of NADPH
- Reductive biosynthesis: plays a crucial role in the synthesis of fatty acids, cholesterol, steroid hormones, and bile salts.
- Reduction of hydrogen peroxide: helps detoxify reactive oxygen species (ROS).
- Cytochrome P450 monooxygenase system: involved in the metabolism of various substances, including drugs and steroids.
- Phagocytosis by white blood cells: supports the activity of phagocytic cells that engulf and destroy pathogens.
- Nitric oxide synthesis: required as a co-factor for nitric oxide synthases.
Glucose 6-Phosphate Dehydrogenase Deficiency
- The most common disease-producing enzyme abnormality among humans.
- Deficiency results in reduced NADPH production in erythrocytes, leading to hemolytic anemia.Oxidative stress, certain drugs, and infections can trigger acute hemolytic crises in individuals with G6PD deficiency.
- G6PD deficiency is caused by various mutations in the gene that codes for the enzyme.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Explore the Pentose Phosphate Pathway, also known as the hexose monophosphate shunt. This quiz covers its functions, key reactions, and the role of NADPH in cellular metabolism. Learn about its two branches and the biochemical processes involved.
