CHEM CH24Metabolic Pathways and Energy Utilization

Glucose and Glycolysis

• Glycolysis is the most common pathway for glucose metabolism.

• However, other pathways exist, such as the lactate pathway.

Lactate Pathway

• The lactate pathway occurs when there is a lack of oxygen (anaerobic conditions).

• Lactate utilization increases during oxygen deficits.

Glucose and Lactate Importance in the Quiz

• Glucose and lactate are heavily emphasized in the quiz.

• Around half the test focuses on glucose and lactate.

Glycolysis Products

• Glucose converts to pyruvate during glycolysis.

• Pyruvate then metabolizes to acetyl CoA.

• Three major products of glycolysis:

  • Pyruvate

  • Acetyl CoA

  • Lactate

• Glucose is NOT a product of glycolysis; it's the starting reactant.

Gluconeogenesis

• Gluconeogenesis: A pathway where glucose is synthesized, essentially reversing glycolysis.

Glycolysis Explained

• When you eat sugar, you get glucose.

• Glucose goes through glycolysis (breaking down of sugar).

• Glycolysis yields pyruvate, acetyl CoA, and sometimes lactate, depending on conditions.

Glucose Storage

• Excess glucose is stored as glycogen in the liver.

• During starvation or low glucose levels, glycogen is converted back to glucose via gluconeogenesis.

Regulation by Hormones

• Glycogen storage and release are carefully regulated by insulin and glucagon.

• Insulin increases when you eat, while glucagon is low.

• When hungry (starvation mode), insulin is low, and glucagon is high (to convert glycogen back to glucose).

• Insulin and glucagon are inversely proportional.

• Insulin carries glucose into the cell.

Brain's Glucose Uptake

• Insulin is NOT needed to transport glucose to the brain; glucose diffuses freely.

Gluconeogenesis Explained

• Gluconeogenesis synthesizes glucose when there aren't enough carbohydrates available.

• It can utilize lactate, amino acids (from protein), and fats to make glucose.

Cori Cycle

• The Cori cycle occurs when muscles are at rest, contributing to glucose levels at a lesser rate.

Fatty Acids for Energy

• Fatty acids are used to burn fats and obtain energy.

• The fatty acids are broken down, producing acetyl CoA units.

• ATP is converted to AMP during fatty acid breakdown, losing two phosphate groups (burning more energy).

  • ATP \rightarrow AMP (loss of two phosphate groups)

• Burning fats requires a lot of energy.

• Fatty acids are long chains, and their catabolic breakdown produces acetyl CoA, which helps make ATP.

Utilization of Fatty Acids

• Fatty acids are used as energy when there are no more carbohydrates to burn.

Ketone Bodies and Ketogenesis

• When not enough carbohydrates are available, the body turns to triglycerides (fats).

• Beta oxidation in fatty acids produces a large amount of acetyl CoA.

• The beta chain of fatty acids has a large amount of acetylcholine. For example, it produces nine acetyl CoA compared to 2 from glucose.

• If the citric acid cycle cannot process all the extra acetyl CoA, it turns into ketone bodies (ketogenesis).

• Small amounts of ketone bodies are fine, but large amounts cause problems.

• Acetyl acetate is a ketone body, and it can turn into acetone.

• Acetone breath is a byproduct of ketone bodies.

• Ketone bodies are soluble in blood and urine. High levels in urine indicate ketosis and starvation.

Keto Diets

• Keto diets are generally safe because you're still eating something; the body isn't pushed to extreme acidosis.

• In pure ketoacidosis (long-term starvation), acid builds up, lowering blood and urine pH.

• Low blood pH denatures proteins and damages organs like kidneys.

• Low pH can also affect the brain, leading to a coma as a protective mechanism.

Diabetic Ketoacidosis

• Diabetic ketoacidosis occurs because, in diabetics, glucose doesn't enter the cell, causing cellular starvation.

• This leads to ketogenesis and acid buildup.

• The brain has enough glucose but shuts down due to acidity in the blood, not lack of glucose.

• Diabetic ketoacidosis is more common in type 1 diabetes.

• Treatment focuses on addressing the acidity with IV fluids.

Metabolic Fates of Glucose Breakdown Products

• Three pathways from glucose breakdown:

  • Pyruvate

  • Acetyl CoA

  • Intermediate pathway (e.g., lactate)

• Remember, these pathways break down glucose, not create it, unless it's gluconeogenesis.