72 Questions
What is the main function of the Electron Transport Chain (ETC)?
Produce metabolic water by combining electrons with O2 and H+.
Why are compounds that inhibit the proteins complexes of the ETC considered lethal?
They disrupt the electron transfer process, leading to cell death.
What is the role of CoQ in the Electron Transport Chain?
Transport electrons between NADH and FADH2.
How is ATP produced in mitochondria through the ETC?
By pumping H+ ions across the inner mitochondrial membrane.
What happens during oxidation in the ETC?
Electrons are removed from electron donors.
Which part of the ETC creates an electrochemical gradient by pumping H+ ions?
Complex I
What happens during reduction in the ETC?
Electrons are gained by electron receptors.
How does the ETC use free energy released by electrons?
To pump H+ ions and create an electrochemical gradient.
What is the primary function of the Pentose Phosphate Pathway (PPP) in the cell?
To produce ribose residues for nucleotide and nucleic acid biosynthesis
Which of the following tissues has the highest activity of the Pentose Phosphate Pathway (PPP)?
Liver and adipose tissue
Which of the following physiological processes is NOT directly dependent on NADPH?
ATP production in the mitochondria
What is the primary function of NADPH in the synthesis of nitric oxide (NO)?
To provide the reducing power for the nitric oxide synthase enzyme
How does NADPH contribute to the maintenance of cellular redox homeostasis?
By regulating the activity of antioxidant enzymes
Which of the following is NOT a major function of NADPH in physiological processes?
Facilitating the transport of oxygen across cell membranes
What is the primary reason for the high activity of the Pentose Phosphate Pathway (PPP) in the lactating mammary gland?
To generate NADPH for the synthesis of milk fats
What is the effect of uncouplers on the relationship between oxidation and phosphorylation?
Uncouplers dissociate oxidation from phosphorylation
What is the role of NADPH in cellular defense mechanisms?
NADPH is used as a reducing agent in antioxidant defense systems
Which of the following is a function of the Pentose Phosphate Pathway (PPP)?
To generate NADPH for cellular defense mechanisms
What is the primary function of NADPH in physiological processes?
To act as a reducing agent in various metabolic processes
Which of the following is a potential function of the respiratory burst in immune cells?
To generate reactive oxygen species for pathogen defense
How does the action of uncouplers differ from the action of respiratory inhibitors?
Uncouplers dissociate oxidation from phosphorylation, while respiratory inhibitors generate heat during hibernation
What is the main function of the Cori Cycle?
Convert lactate into glucose in the liver
What is the primary storage organ for glycogen in the body?
Liver
Which enzyme is responsible for starting the glycogen chain during glycogenesis?
Glycogenin
What is the alternate name for the Pentose Phosphate Pathway (PPP)?
Hexose Monophosphate Shunt
Which hormone stimulates glycogenolysis and inhibits glycogenesis?
Glucagon
What is the main source of substrate for gluconeogenesis?
Lactate from anaerobic glycolysis
Which enzyme elongates the glycogen chain during glycogenesis?
Glycogen synthase
What is the primary location of gluconeogenesis in the body?
Liver
Which of the following substrates is NOT used in gluconeogenesis?
Glucose
Why is gluconeogenesis not considered the reverse of glycolysis?
Gluconeogenesis uses different enzymatic pathways than glycolysis.
Which of the following hormones stimulates gluconeogenesis?
Glucagon
What is the primary function of the TCA cycle in the context of gluconeogenesis?
To convert glucogenic amino acids into oxaloacetate
Which of the following molecules is NOT a substrate for gluconeogenesis?
Glucose
What is the primary purpose of gluconeogenesis in the body?
To maintain plasma glucose levels between meals
Which of the following amino acids is NOT considered a glucogenic amino acid?
Glucose
What is the primary effect of UNCOUPLERS on cellular respiration?
Generate heat without ATP production
Which of the following substances inhibits Complex IV in the electron transport chain?
Cyanide
How do UNCOUPLERS affect the relationship between oxidation and phosphorylation?
Dissociate oxidation from phosphorylation
Where does gluconeogenesis primarily occur in the body?
Liver
What is the main function of ATP synthase in oxidative phosphorylation?
ATP synthesis
Which of the following is an inhibitor of Complex I in the electron transport chain?
Rotenone
What is the purpose of generating heat without ATP production in cells?
Maintain body temperature
What primarily regulates OXPHOS based on the energy needs of the cell?
ATP/ADP ratio
Which hormone stimulates gluconeogenesis and inhibits insulin in the context of glucose metabolism?
Glucagon
What is the primary substrate used for gluconeogenesis from TAG breakdown?
Glycerol
Which compound is responsible for creating an electrochemical gradient during OXPHOS?
Proton (H+) ions
What is the primary role of ATP synthase in cellular respiration?
Generating ATP
Which amino acid is NOT considered a substrate for gluconeogenesis?
Leucine
Which of the following compounds is known to uncouple electron transport from ATP synthesis in mitochondria?
DNP (2,4-Dinitrophenol)
What inhibits gluconeogenesis during glucose metabolism?
Citrate
What is the main function of ATP synthase in the context of oxidative phosphorylation?
Creating an electrochemical gradient by pumping H+ ions
Which pathway provides an important source of substrate for gluconeogenesis?
Cori Cycle
What is the primary reason for the high activity of the Pentose Phosphate Pathway (PPP) in certain metabolic processes?
Generating NADPH for biosynthetic reactions and antioxidant defense
Which of the following is NOT considered an inhibitor of Oxidative Phosphorylation?
NADPH
How do uncouplers affect the relationship between electron transport and ATP synthesis in mitochondria?
Decrease ATP production despite increased electron transport
Which enzyme is responsible for initiating the glycogen chain during glycogenesis?
Glycogenin
'Glucose 6-phosphate' as a substrate in Glucose metabolism is primarily associated with which pathway?
Pentose Phosphate Pathway
What is the primary function of ATP synthase in the Electron Transport Chain (ETC)?
It converts the energy released from the electrochemical gradient into the phosphorylation of ADP to produce ATP.
Which of the following is a primary function of the Pentose Phosphate Pathway (PPP) in the cell?
To produce NADPH for reductive biosynthesis and cellular defense mechanisms.
What is the primary role of gluconeogenesis in the body?
To convert amino acids and other non-carbohydrate precursors into glucose.
How do uncouplers differ from respiratory inhibitors in their effects on the Electron Transport Chain (ETC)?
Uncouplers disrupt the coupling between oxidation and phosphorylation, while respiratory inhibitors block specific complexes in the ETC.
Which part of the Electron Transport Chain (ETC) is responsible for pumping H+ ions across the inner mitochondrial membrane to create an electrochemical gradient?
Complex I (NADH dehydrogenase)
How does the Electron Transport Chain (ETC) use the free energy released by the transfer of electrons?
The free energy is used to pump H+ ions across the inner mitochondrial membrane, creating an electrochemical gradient.
Why are compounds that inhibit the protein complexes of the Electron Transport Chain (ETC) considered lethal?
They block the transfer of electrons through the ETC, preventing the reduction of oxygen to water.
What is the primary function of the Pentose Phosphate Pathway (PPP) in the cell?
Generation of NADPH for reductive biosynthesis
Which of the following tissues has the highest activity of the Pentose Phosphate Pathway (PPP)?
Adipose tissue
What is the primary role of NADPH in the respiratory burst process?
Production of reactive oxygen species (ROS) like H2O2
Which of the following is NOT a substrate for gluconeogenesis?
Fatty acids
What is the primary function of ATP synthase?
Synthesis of ATP from ADP and Pi
How does the action of uncouplers differ from the action of respiratory inhibitors?
Uncouplers disrupt the proton gradient, while inhibitors block electron flow
What is the primary regulation point of the TCA cycle?
The conversion of α-ketoglutarate to succinyl-CoA
Study Notes
Electron Transport Chain (Respiratory Chain)
- Passes electrons from NADH and FADH2 to protein complexes and mobile electron carriers (CoQ and cytochrome C)
- Electrons ultimately combine with O2 and H+ to form H2O (metabolic water)
- Requires O2, making it the major consumer of oxygen in mammalian cells
- 4 transmembrane enzymatic complexes + 2 mobile electron carriers (CoQ, cytochrome C)
- Electron-transporting groups contain iron, sulfur, copper
- All are proteins except for CoQ
- Free energy released by electrons is used to pump H+
- Electrons are transferred from electron donor to electron receptor
- Oxidation → electrons are removed, Reduction → electrons are gained
- Phosphorylation of ADP to ATP:
- Pumps H+ from matrix across inner mitochondrial membrane at complexes I, III, and IV
- Creates an electrochemical gradient
- Energy created moves ATP synthase
- Generates NADPH for reductive biosynthesis of lipids (fatty acids, cholesterol, and steroids)
- Provides ribose residues for nucleotide and nucleic acid biosynthesis (ATP, NAD+, FAD, RNA, and DNA)
The Pentose Phosphate Pathway (PPP)
- Occurs in cell cytosol, no ATP is consumed or generated
- High activity in:
- Liver and adipose tissue: biosynthesis of fatty acids from acetyl-CoA
- Endocrine tissues: synthesis of cholesterol and steroid hormones
- Lactating mammary gland: production of milk fats and proteins
- Mature erythrocyte, lens and cornea: glutathione production (oxidative damage protection)
NADP+/NADPH
- Important source of electrons (reducing/oxidizing agent)
- Contributes to maintenance of cellular redox homeostasis
- Reduces cytochrome P450 (drug metabolism in liver)
- Synthesizes Nitric Oxide (NO) for smooth muscle relaxation, neurotransmission, and bactericidal activity
- Involved in lipogenesis, synthesis of steroids and fatty acids
- Participates in respiratory burst in phagocytic cells (NADPH-oxidase)
Glycogen Metabolism
- Glycogenesis: stores glucose as glycogen
- Main stores in liver (up to 10% of liver weight) and skeletal muscle (up to 1% of muscle weight)
- Glycogenolysis: glycogen mobilization from glycogen stores
- Occurs when blood glucose levels are low (i.e., fasting)
- Glycogen synthesis occurs in cell cytosol, each molecule contains around 60,000 glucose residues and is highly hydrophilic
- Important enzymes for synthesis: glycogenin (primer), glycogen synthase (elongate chain), and branching enzyme
- Glycogen storage diseases are associated with enzyme deficiencies
- Prolonged use of steroids can cause glycogen storage abnormalities
- Regulation: insulin (anabolic) stimulates glycogenesis and inhibits glycogenolysis, while glucagon (and epinephrine) (catabolic) stimulates glycogenolysis and inhibits glycogenesis
Cori Cycle and Gluconeogenesis
- Cori cycle: lactate produced by anaerobic glycolysis is transported to the liver and converted to glucose (gluconeogenesis pathway)
- Prevents lactic acidosis during anaerobic conditions in muscle
- Important source of substrate for gluconeogenesis
- Gluconeogenesis: production of glucose from non-sugar molecules
- Supplies plasma glucose needs between meals and during prolonged fasting
- Continuous process in carnivores and ruminants
- Hormone-controlled (stimulated by glucagon and epinephrine, inhibited by insulin)
- Substrates: lactate, pyruvate, glycerol, and glucogenic amino acids (e.g., alanine, arginine, aspartate)
ATP Synthase and Oxidative Phosphorylation Inhibitors and Uncouplers
- ATP synthase: multi-subunit enzyme that rotates to synthesize ATP from ADP and Pi
- Oxidative phosphorylation inhibitors:
- Complex I: barbiturate, insecticide (rotenone)
- Complex II: malonate, carboxin, and TTFA (Fe-chelating agent)
- Complex III: dimercaprol, antimycin
- Complex IV: hydrogen sulfide (H2S), carbon monoxide (CO), and cyanide
- Uncouplers dissociate oxidation from phosphorylation, generating heat instead of ATP
Learn about the significance of the Pentose Phosphate Pathway (PPP) in providing NADPH for reductive biosynthesis of lipids and ribose residues for nucleotide and nucleic acid biosynthesis. Understand where PPP occurs and its high activity in specific tissues such as liver, adipose tissue, and endocrine tissues.
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