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Questions and Answers
What is the main product of glycolysis?
What is the main product of glycolysis?
Pyruvate
Which of the following is NOT a monosaccharide that can be broken down into glucose during glycolysis?
Which of the following is NOT a monosaccharide that can be broken down into glucose during glycolysis?
Glycolysis takes place in the mitochondria.
Glycolysis takes place in the mitochondria.
False
Name one key enzyme that regulates the rate of glycolysis.
Name one key enzyme that regulates the rate of glycolysis.
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Which of the following is NOT one of the possible fates of pyruvate under anaerobic conditions?
Which of the following is NOT one of the possible fates of pyruvate under anaerobic conditions?
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What are the two main types of fermentation?
What are the two main types of fermentation?
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Gluconeogenesis can be considered a complete reversal of glycolysis.
Gluconeogenesis can be considered a complete reversal of glycolysis.
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What is the primary fuel for the brain and the only fuel for red blood cells?
What is the primary fuel for the brain and the only fuel for red blood cells?
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Which of the following is not a precursor for gluconeogenesis?
Which of the following is not a precursor for gluconeogenesis?
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The Warburg effect refers to cancer cells using glycolysis under aerobic conditions.
The Warburg effect refers to cancer cells using glycolysis under aerobic conditions.
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What is the name of the cycle that describes the interplay between glycolysis in muscle and gluconeogenesis in the liver?
What is the name of the cycle that describes the interplay between glycolysis in muscle and gluconeogenesis in the liver?
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How many NTPs are required to form one glucose molecule from pyruvate during gluconeogenesis?
How many NTPs are required to form one glucose molecule from pyruvate during gluconeogenesis?
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Which statement best describes the relationship between glycolysis and gluconeogenesis?
Which statement best describes the relationship between glycolysis and gluconeogenesis?
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What role does hexokinase play in the glycolysis pathway?
What role does hexokinase play in the glycolysis pathway?
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Why is glucose considered a stable source of energy for biochemical processes?
Why is glucose considered a stable source of energy for biochemical processes?
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Which phase of glycolysis involves the conversion of glucose to glyceraldehyde-3-phosphate?
Which phase of glycolysis involves the conversion of glucose to glyceraldehyde-3-phosphate?
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What is the main function of induced fit in the enzyme hexokinase?
What is the main function of induced fit in the enzyme hexokinase?
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What potential outcomes can result from the metabolism of pyruvate?
What potential outcomes can result from the metabolism of pyruvate?
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What key advantage does glucose have in the context of prebiotic conditions?
What key advantage does glucose have in the context of prebiotic conditions?
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How do different cell types respond to glycolysis?
How do different cell types respond to glycolysis?
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What compound forms when galactose is converted in the lens of the eye?
What compound forms when galactose is converted in the lens of the eye?
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During gluconeogenesis, which of the following is NOT a common precursor used to generate glucose?
During gluconeogenesis, which of the following is NOT a common precursor used to generate glucose?
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Which organ is primarily responsible for gluconeogenesis?
Which organ is primarily responsible for gluconeogenesis?
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What is the primary carbohydrate utilized by the brain each day?
What is the primary carbohydrate utilized by the brain each day?
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What causes water to diffuse into the lens of the eye, leading to cataract formation?
What causes water to diffuse into the lens of the eye, leading to cataract formation?
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What is the role of debranching enzymes in glycogen metabolism?
What is the role of debranching enzymes in glycogen metabolism?
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Which statement about gluconeogenesis during fasting is true?
Which statement about gluconeogenesis during fasting is true?
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Which of the following statements about energy yields from glycogen is incorrect?
Which of the following statements about energy yields from glycogen is incorrect?
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What percentage of glucose is typically consumed by the brain each day out of the total glucose requirement?
What percentage of glucose is typically consumed by the brain each day out of the total glucose requirement?
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What is the final outcome of glycolysis when starting with 1 molecule of glucose?
What is the final outcome of glycolysis when starting with 1 molecule of glucose?
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What is the role of NAD+ in anaerobic conditions during glycolysis?
What is the role of NAD+ in anaerobic conditions during glycolysis?
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Which statement is correct regarding the fates of pyruvate?
Which statement is correct regarding the fates of pyruvate?
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What is the essential step following the isomerization of 3-phosphoglycerate in glycolysis?
What is the essential step following the isomerization of 3-phosphoglycerate in glycolysis?
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In aerobic metabolism, how is NAD+ restored after glycolysis?
In aerobic metabolism, how is NAD+ restored after glycolysis?
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Which of the following accurately describes the produced gas in alcoholic fermentation?
Which of the following accurately describes the produced gas in alcoholic fermentation?
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What key intermediate is involved in the transition of pyruvate to the citric acid cycle?
What key intermediate is involved in the transition of pyruvate to the citric acid cycle?
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What type of organisms primarily utilize lactic acid fermentation?
What type of organisms primarily utilize lactic acid fermentation?
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What is the function of the electron transport chain in aerobic metabolism?
What is the function of the electron transport chain in aerobic metabolism?
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Which enzyme is responsible for replacing the pyruvate kinase reaction in gluconeogenesis?
Which enzyme is responsible for replacing the pyruvate kinase reaction in gluconeogenesis?
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What is the overall Gibbs free energy change ($ΔG$) for gluconeogenesis?
What is the overall Gibbs free energy change ($ΔG$) for gluconeogenesis?
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In which cellular location does pyruvate carboxylase operate?
In which cellular location does pyruvate carboxylase operate?
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Which of the following statements about gluconeogenesis is true?
Which of the following statements about gluconeogenesis is true?
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What is the role of biotin in the action of pyruvate carboxylase?
What is the role of biotin in the action of pyruvate carboxylase?
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Which step of gluconeogenesis involves fructose-1,6-bisphosphatase?
Which step of gluconeogenesis involves fructose-1,6-bisphosphatase?
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What important function does glucose-6-phosphatase serve in gluconeogenesis?
What important function does glucose-6-phosphatase serve in gluconeogenesis?
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Which of the following correctly describes gluconeogenesis in relation to glycolysis?
Which of the following correctly describes gluconeogenesis in relation to glycolysis?
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What is necessary for the conversion of pyruvate to oxaloacetate?
What is necessary for the conversion of pyruvate to oxaloacetate?
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How does the Gibbs free energy change ($ΔG$) for glycolysis compare to that for gluconeogenesis?
How does the Gibbs free energy change ($ΔG$) for glycolysis compare to that for gluconeogenesis?
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Study Notes
Carbohydrate Metabolism
- Carbohydrates are a crucial energy source for most organisms
- Glucose is the primary fuel for the brain and red blood cells
- Glucose metabolism involves glycolysis, a ten-step process, converting glucose into pyruvate, generating ATP and NADH.
- Three possible fates of pyruvate: reduction to lactate, reduction to ethanol, or oxidation to form CO2 and H2O.
- Anaerobic conditions lead to fermentation (producing lactate or ethanol)
- Aerobic conditions lead to the citric acid cycle and electron transport chain for complete oxidation of pyruvate.
- Glycogen breakdown releases glucose for energy use.
- Glycogen is stored in the liver and muscle.
- Other monosaccharides (galactose, fructose, mannose) enter glycolysis via conversion to glycolytic intermediates.
- Polysaccharides are digested to form monosaccharides before entering the metabolic pathways.
Glucose Metabolism
- Glycolysis occurs in the cytosol. It is a ten-step process. The process is also called the Embden-Meyerhof pathway.
- It converts one glucose molecule to two pyruvate molecules.
- Essentially all cells carry out glycolysis but with differing rates.
- Glycolysis has two phases: the investment phase that converts glucose to glyceraldehyde-3-P, and the paid-off phase that produces two pyruvates.
- The products are pyruvate, ATP and NADH.
- This process has three possible fates for the produced pyruvate.
Lipid Metabolism
- Lipids are also essential for energy storage and cellular processes.
- Fatty acids are broken down through beta-oxidation to generate acetyl-CoA for energy production.
- The citric acid cycle plays a role in both carbohydrate and lipid metabolism.
Pentose Phosphate Pathway
- This pathway has two phases, an oxidative and a non-oxidative phase.
- The oxidative part is responsible for NADPH synthesis, a crucial electron carrier for biosynthesis.
- The non-oxidative part interconverts sugars with different numbers of carbons.
- This pathway is important for producing NADPH for reductive biosynthesis in fatty acids and steroids.
- It is also crucial for generating Ribose-5-phosphate, needed for nucleotide synthesis.
Gluconeogenesis
- Gluconeogenesis is the biosynthesis of glucose from non-carbohydrate precursors, essential for maintaining blood glucose levels during fasting or starvation.
- It is almost the opposite process to glycolysis.
- It utilizes several enzymes not found in glycolysis.
- Crucial steps differ from glycolysis with different enzymes and substrates.
- It uses different enzymes in 3 steps. Examples include:
- Pyruvate carboxylase and PEP carboxykinase
- Fructose-1,6-bisphosphatase
- Glucose-6-phosphatase
- The process is energetically unfavorable and requires 6 NTPs (nucleoside triphosphate) for each glucose molecule.
- The process occurs in the liver, with some occurring in the kidneys.
- Relies on alternative pathways of glycolysis.
Fermentation
- Fermentation occurs when oxygen is not available.
- Two main types of fermentation are alcoholic fermentation and lactic acid fermentation.
- These processes regenerate NAD+ from NADH so glycolysis can proceed in the absence of oxygen.
- Fermentation processes happen in different situations including intense exercise.
Important Enzymes (Examples)
- Hexokinase: traps glucose in the cell
- Phosphofructokinase: catalyzes an irreversible reaction in glycolysis
- Lactate dehydrogenase: converts pyruvate to lactate or lactate to pyruvate (in the liver)
- Glucose-6-phosphate dehydrogenase: produces NADPH in the pentose phosphate pathway
- Gluconolactonase / 6-phosphogluconate dehydrogenase
- Pyruvate carboxylase : a key enzyme in gluconeogenesis.
- Phosphopentose isomerase: converts ribulose 5-phosphate to ribose 5-phosphate.
- Phosphopentose epimerase: converts ribulose to xylulose.
- Transketolase: transfers two-carbon units.
- Transaldolase: responsible for transferring three-carbon units.
Roles of Specific Compounds
- NADH: a coenzyme that carries electrons to the electron transport chain. Crucial in both glycolysis and further respiration (aerobic or anaerobic).
- ATP: a high-energy molecule that stores chemical energy from glucose breakdown and fuels cellular processes.
- NADPH: Important in reduction reactions, biosynthesis, especially fatty acids and steriods.
- Ribose 5 phosphate (R5P): crucial for nucleotide synthesis.
- GTP: A key nucleotide triphosphate involved in gluconeogenesis.
Other Important Concepts
- Warburg effect: Cancer cells preferentially metabolize glucose to lactate even in the presence of oxygen.
- This process is due to an increased requirement for NADPH for biosynthesis.
- Cori cycle: The exchange of lactate between muscles and the liver.
- Respiration quotient (RQ): A measurement of the fuel source used during cellular respiration.
- Reactive oxygen species (ROS): Harmful oxygen-containing molecules that are naturally generated in the body.
- Glucose 6-phosphate dehydrogenase (G6PD) deficiency: this deficiency results in a lack of NADPH production and sensitivity to oxidative stress. G6PD deficiency is particularly a protective mechanism against malaria due to the lack of NADPH causing harm to the parasite.
Regulation
- Glycolysis and gluconeogenesis are reciprocally regulated to prevent concurrent activation to prevent futile cycles.
- Cellular levels of glucose/energy levels, and hormones affect the rate of these pathways.
Special Cases
- Red blood cells (RBCs): Lack mitochondria and exclusively rely on glycolysis for ATP production.
- Hummingbirds: High activity requires high NADPH, therefore use the pentose phosphate pathway at higher rates than most other animals.
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Description
Explore the intricate processes of carbohydrate metabolism, focusing on glucose metabolism, glycolysis, and the fate of pyruvate. Understand how anaerobic and aerobic conditions influence energy production through fermentation and the citric acid cycle. This quiz will test your knowledge about energy sources and metabolic pathways.
