Metabolism and Glucose Catabolism Quiz

Metabolism

• Metabolism encompasses all chemical processes within an organism to sustain life, involving converting food to energy and the life-sustaining chemical reactions.
• It involves two main processes: catabolism and anabolism.
  • Catabolism breaks down complex organic compounds to release energy.
  • Anabolism uses energy to synthesize complex molecules from simpler ones.
• ATP (adenosine triphosphate) plays a central role in energy exchange.
• Cells have billions of ATP molecules to quickly produce energy.
• Half the energy released is lost as heat.
• Energy is found in bonds between atoms. Oxidation is a decrease in a molecule's energy content (electron loss and H+). Reduction is an increase (electron gain and H+).
  • Oxidation-reduction (redox) reactions are always coupled in the body.

Four Steps of Glucose Catabolism

• Glycolysis, the breakdown of glucose (in cytosol).

• Formation of acetyl coenzyme A (in mitochondrial matrix)

• Krebs cycle (in mitochondrial matrix)

• Electron transport chain (ETC) (in inner mitochondrial membrane)

• One glucose molecule produces 36 or 38 ATP.

The Respiratory Quotient (RQ)

• RQ measures the rate of CO₂ production to O₂ consumption.
• RQ values vary with different food types (carbohydrates, fats, and proteins).

Direct and Indirect Calorimetry

• Direct calorimetry measures heat production, while indirect calorimetry measures O₂ consumption and CO₂ production.

The Electron Transport Chain (ETC)

• A series of membrane proteins in the inner mitochondrial membrane.
• The ETC facilitates oxidation-reduction reactions, transferring electrons to make an H+ gradient.
• The H+ gradient is used to produce ATP through chemiosmosis.

Liver Functions

• Metabolism and storage of carbohydrates, proteins, and fats
• Detoxifies blood by removing or altering drugs and hormones (including thyroid and estrogen).
• Removes bilirubin from the breakdown of red blood cells.
• Releases bile salts for digestion.
• Stores fat-soluble vitamins (A, D3, E, and K).
• Stores iron and vitamin B12.
• Removes worn-out blood cells and bacteria (phagocytosis).
• Plays a role in vitamin D activation.

Overview of Glucose Metabolism

• Glycolysis: Breakdown of glucose to pyruvate or lactate.
• Glycogenolysis: Breakdown of glycogen to glucose.
• Glycogenesis: Formation of glycogen from glucose.
• Gluconeogenesis: Formation of new glucose from other substances (e.g., amino acids, glycerol).

Glycogenesis vs. Glycogenolysis

• Glycogenesis (stimulated by insulin): glucose to glycogen synthesis
• Glycogenolysis (stimulated by glucagon and epinephrine): glycogen to glucose breakdown

Glycolysis vs. Gluconeogenesis

• Glycolysis is the breakdown of glucose, while gluconeogenesis is the formation of glucose from other metabolites.
• Glycolysis uses glucose to produce pyruvate, while gluconeogenesis creates glucose from pyruvate and other sources.

Transport of Lipids by Lipoproteins

• Lipids are transported in the blood as lipoproteins, which combine with proteins.
• Lipoproteins are categorized by density.
• Lipoproteins include chylomicrons, VLDLs, LDLs, and HDLs.

Fate of Lipids

• Oxidation for ATP production.
• Storage in adipose tissue or the liver.
• Synthesis of structural molecules (phospholipids, lipoproteins, thromboplastin, myelin sheaths).
• Synthesis of bile salts and steroid hormones .

Overview of Lipid Metabolism

• Lipolysis: breakdown of triglycerides into glycerol and fatty acids.
• Beta Oxidation: Fatty acids are broken down into acetyl-CoA.
• Lipogenesis: synthesis of triglycerides from fatty acids and glycerol, amino acids.

Lipolysis

• Lipids undergo beta oxidation, breaking them down to produce acetyl-CoA.
• Ketogenesis: occurs in liver cells and produces ketone bodies, which are used by heart muscle and the kidney cortex for energy production.

Lipogenesis

• Synthesis of triglycerides from fatty acids and glycerol.
• Uses fuel sources like amino acids, glycolysis metabolites, and ketone bodies.

Fate of Proteins

• Proteins are broken down into amino acids.
• Amino acids can be deaminated to enter the Krebs cycle.
• Amino acids can be used to synthesize new proteins throughout the body.
• Excess amino acids may be converted to glucose or triglycerides.
• Absorption of amino acids into body cells is stimulated by insulin-like growth factors (IGFs) and insulin.

Metabolic Functions of the Liver – Part 1

• Carbohydrate Metabolism:
  • Converts amino acids to glucose (gluconeogenesis).
  • Converts triglycerides to glucose (gluconeogenesis).
  • Stores excess glucose as glycogen (glycogenesis).
  • Converts glycogen back to glucose (glycogenolysis) as needed.
• Lipid Metabolism:
  • Synthesizes cholesterol.
  • Synthesizes lipoproteins (e.g., HDL and LDL) to transport fatty acids and cholesterol.
  • Stores fat (lipogenesis).
  • Breaks down fatty acids (beta-oxidation).

Metabolic Functions of the Liver – Part 2

• Protein Metabolism:
  • Deamination: Removes an amino group from amino acids to create urea for excretion.
  • Transamination: Transfer of an amino group from one amino acid to another.
  • Synthesizes plasma proteins needed for clotting and the immune system.

Absorptive State

• The time after a meal when nutrients enter the bloodstream and need to be stored.
• The hepatic portal system is used for the absorption of glucose and amino acids.
• Lacteals are used for the absorption of dietary fats.

Absorptive State Summary

• Storage of excess fuels (glucose, lipids, and amino acids)
• Glucose converted to glycogen or triglycerides.
• Dietary lipids are stored in adipose tissue.
• Amino acids are deaminated or converted to glucose/fatty acids.
• Excess amino acids are used by other cells for protein synthesis.

Postabsorptive State

• The state after a few hours after absorbing nutrients.
• The body relies on stored fuels to maintain blood glucose levels.
• Liver's role is crucial as it converts glycogen back into glucose.
• Glucose is also produced through gluconeogenesis from glycerol, amino acids and lactic acid.
• Fatty acids and ketone bodies become important sources of energy.

Postabsorptive State Summary

• Glucose enters the bloodstream from the liver via glycogenolysis and gluconeogenesis.
• Amino acids and lactic acid from muscle are also used for glucose production.
• Alternative fuel source: fatty acids fed into Krebs cycle and ketone body oxidation.