Why does the body need a constant supply of glucose?
Because glucose is essential for survival:
The body uses ~180 g of glucose per day
The brain depends heavily on glucose
Red blood cells rely only on glucose for energy
Why can’t the body rely only on stored glucose?
Because storage is limited:
Blood glucose ≈ 20 g
Glycogen ≈ 200 g (about 1 day’s supply)
Once glycogen is depleted, new glucose must be made
What is gluconeogenesis?
It is the process of synthesizing glucose from non-carbohydrate sources, allowing blood glucose to be maintained during fasting or starvation
When is gluconeogenesis especially important?
During fasting or starvation
After prolonged exercise
When glycogen stores are depleted
What substances can be used to make glucose?
Lactate and pyruvate
Most amino acids
Glycerol
TCA cycle intermediates
Why can’t fatty acids be converted into glucose in humans?
Because fatty acids are broken down into acetyl-CoA, which cannot be converted back into glucose in animal
Where does gluconeogenesis mainly occur?
Liver (major site)
Kidney (minor site
Why don’t brain, muscle, heart, and RBCs perform gluconeogenesis?
These tissues consume glucose for energy but lack key enzymes needed to produce and release glucose
Why must glucose continue to be produced even during fasting?
Brain and RBC energy
Glycogen synthesis
Pentose phosphate pathway (NADPH production)
Biosynthesis of fatty acids, amino acids, and nucleotides
What is the Cori cycle?
A glucose–lactate recycling system between muscle and liver
Cork Cycle steps?
Muscle converts glucose → lactate during intense exercise
Lactate enters blood
Liver takes up lactate
Liver converts lactate → glucose
Glucose returns to muscle
Why is the Cori cycle important?
Prevents lactate accumulation
Maintains blood glucose during exercise
: Why is gluconeogenesis not simply the reverse of glycolysis?
Because glycolysis is highly exergonic; reversing it would require too much energy and would not occur spontaneously
How does gluconeogenesis bypass irreversible glycolysis steps?
It uses different enzymes to bypass the irreversible reactions
Which glycolysis enzymes are irreversible?
Hexokinase
PFK-1
Pyruvate kinase
What enzymes bypass these steps in gluconeogenesis?
Glucose-6-phosphatase
Fructose-1,6-bisphosphatase
Pyruvate carboxylase + PEP carboxykinase
What is the role of glucose-6-phosphatase?
It converts glucose-6-phosphate into free glucose that can be released into the blood
Why can only liver and kidney release glucose into blood?
Because only they contain glucose-6-phosphatase
Why must glycolysis and gluconeogenesis not occur simultaneously?
Running both together would waste energy in a futile cycle
How does the body prevent futile cycling?
Allosteric regulation
Energy charge
Hormonal contro
How does cellular energy status affect gluconeogenesis?
High ATP and acetyl-CoA → gluconeogenesis favored
Low energy → glycolysis favored
What activates pyruvate carboxylase?
High acetyl-CoA, signaling abundant energy and need for glucose production
How does insulin affect gluconeogenesis?
Inhibits gluconeogenesis
Stimulates glycolysis and glucose storage
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1 - Glycolysis104
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1 - Gluconeogenesis36
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1 - Glossary49
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1 - Evolution Concepts And Vocabulary65
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2 - Life Cycle Of Protein Funcation45
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2 - Protein Regulation (Covalent)61
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2 - Protein Regulation (Non-Covalent)72
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3 - Citric Acid Cycle (TCA / Krebs / CAC)58
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3 - Pyruvate Dehydrogenase Complex (PDC)56
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3 - Oxidative Phosphorylation76
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4 - Protein Turnover and Amino Acid Catabolism71
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4 - Fatty Acid Synthesis & Ketone Bodies105
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4 - Fatty Acid Oxidation (β-Oxidation)112
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5 - Glycogen Metabolsim142
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5 - Integration of Energy Metabolism I0
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5 - Integration of Energy Metabolism II0
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7 - Light Reactions I1
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7 - Light Reactions II1
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7 - Light Reactions III1
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8 - Plant Metabolism and Global Food Security1
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8 - C3 Photosynthesis (Calvin Cycle, Sucrose, Starch)1
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8 - Enhanced CO₂ Assimilation (C4, CAM, CCMs)1
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8 - Crassulacean Acid Metabolism Vocabulary1
