Questions and Answers
What is the function of glycolysis?
To convert glucose to three carbon compounds with the formation of ATP.
Where does glycolysis occur?
In all cells and in the cytosol.
How many reactions are in glycolysis?
Ten.
What does glycolysis do?
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Do you lose ATP in glycolysis?
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How many oxidative steps are there in glycolysis, and what happens in this step?
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What are the several metabolic fates of pyruvate?
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What is the regulation of glycolysis exerted on?
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What is the most important rate limiting step in glycolysis?
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What happens to pyruvate under aerobic and anaerobic conditions?
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What are the two big organs for gluconeogenesis?
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In regards to ATP, what is the difference between glycolysis and gluconeogenesis?
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Why can't we reverse all of glycolysis?
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What is known as the synthesis of glucose from 3-carbon molecules such as pyruvate, lactate, and glycol?
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Where does gluconeogenesis occur?
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How many reactions does it take to convert pyruvate to glucose?
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How many reactions of gluconeogenesis are catalyzed by the same enzymes as glycolysis?
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In glycolysis, what enzyme is used to catalyze pyruvate to phosphoenol, and how is this different from gluconeogenesis?
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Hormonal and dietary regulation is exerted on which enzymes?
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How does activation of pyruvate carboxylase occur?
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Pyruvate to oxaloacetic acid is regulated by which enzyme?
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The conversion of two moles of pyruvate to one mole of glucose requires how many moles of ATP and NADH?
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What are usually the substrates used in gluconeogenesis?
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Liver can oxidize lactate to form what?
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Describe the cori cycle.
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Insulin increases glycolysis and decreases gluconeogenesis.
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What are the levels of glucocorticosteroids and glucagon in the two cycles?
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Several hours after a meal, there is a switch from glycolysis to gluconeogenesis. How is this regulated?
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Study Notes
Glycolysis Overview
- Glycolysis transforms glucose into three-carbon compounds, producing ATP.
- Occurs in all cells within the cytosol.
- Comprises ten reactions, ultimately converting glucose into pyruvate.
- No ATP is lost; there is a net production of ATP.
- One oxidative step takes place, where NAD is reduced to NADH.
Metabolic Fate of Pyruvate
- Pyruvate can be converted to lactate under anaerobic conditions by lactate dehydrogenase.
- It can lose a CO2 molecule to become ethanol.
- Under aerobic conditions, pyruvate forms acetyl coenzyme A through pyruvate dehydrogenase.
- Alternatively, pyruvate can form oxaloacetate via pyruvate carboxylase.
Regulation of Glycolysis
- Regulated at three irreversible steps involving hexokinase, phosphofructokinase, and pyruvate kinase.
- Phosphofructokinase is crucial as the rate-limiting step; influenced by ATP concentrations.
Aerobic vs Anaerobic Conditions
- Anaerobic conditions convert pyruvate to lactate, regenerating NAD from NADH.
- Aerobic conditions oxidize pyruvate to acetyl CoA, which enters the citric acid cycle.
Gluconeogenesis Basics
- Primarily occurs in the liver and kidneys.
- ATP-consuming process to synthesize glucose from three-carbon precursors like pyruvate and lactate.
- Transformation of pyruvate to glucose uses eleven reactions, with seven shared with glycolysis.
Key Enzymes in Gluconeogenesis
- Enzymes specific to gluconeogenesis include pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and fructose-1,6-bisphosphate, among others.
- Pyruvate carboxylase activation requires acetyl CoA.
Energy Requirements
- Converting two moles of pyruvate to one mole of glucose consumes six ATP molecules and two NADH.
- Lactate, pyruvate, and glycerol are common substrates in gluconeogenesis.
Further Insights
- The Cori cycle connects muscle and liver metabolism; lactate produced in muscles during exercise is transported to the liver, where it is converted back to pyruvate.
- Insulin facilitates glycolysis, while gluconeogenesis is promoted by glucocorticoids and glucagon.
Hormonal Regulation
- Glucagon increases gluconeogenesis and decreases glycolysis.
- After meals, there's a regulatory switch from glycolysis to gluconeogenesis facilitated by hormonal changes, particularly glucagon and insulin, through protein phosphorylation.
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Test your knowledge on glycolysis and gluconeogenesis with these flashcards. Each card provides essential functions, locations, and processes involved in glycolysis. Ideal for students looking to strengthen their understanding of carbohydrate metabolism.