Molecular Biology of Energy Metabolism

Course Information

• Course Title: BIO 111 General Biology I
• Topic: Energy Production and Utilization
• Prepared by: Dr. B.P Olatunji
• Institution: University of Medical Sciences, Ondo City, Ondo State, Nigeria

Introduction to Energy Production

• Food provides energy, but the process is complex
• Cells must adjust to fluctuating energy needs of the body

General Objectives

• Identify cells requiring energy
• Explain energy utilization and production in different cells
• Explain how blood glucose levels are maintained

Carbohydrate Metabolism

• Organisms break down carbohydrates for cellular energy
• Photosynthetic plants produce carbohydrates
• Glucose breakdown: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
• Photosynthesis: 6CO₂ + 6H₂O + energy → C₆H₁₂O₆ + 6O₂

Key Terms

• Adenosine triphosphate (ATP): multifunctional molecule, the "molecular unit of energy currency" in intracellular transfer
• Glucose: simple monosaccharide (sugar), C₆H₁₂O₆, major energy source

Carbohydrates

• Major energy source for organisms
• Starch: chief carbohydrate in human food, glucose storage form in plants
• Plants store starch when available, later using it as needed
• Glycogen: glucose storage polysaccharide in animals, up to 10% of liver mass, 1% muscle mass

Carbohydrate Tips

• Glycogen is larger and more branched than amylopectin
• Enzymes like amylase, α(1-4), amylo(1→6) glucosidase, and α(1→4) glucosidase break down starch and glycogen into glucose
• Cells primarily use glucose

Additional Carbohydrate Information

• Glucose, fructose, and galactose are primary monosaccharides from digestion
• Fructose and galactose converted to glucose by the liver
• Pentose sugars (xylose, arabinose, ribose) may be present in the diet, but their fate after absorption is unclear

Metabolism of Carbohydrates in Animals and Plants

• Plants use sunlight to make carbohydrates (photosynthesis)
• Animals get carbohydrates from plants or other animals
• Plants store carbohydrates as starch; animals store as glycogen

Metabolism of Carbohydrates (Glycolysis and Citric Acid Cycle)

• Glycolysis: converts glucose to pyruvate, capturing energy as ATP
• Citric acid cycle: the final common oxidative pathway for carbohydrates, fats, and proteins, also supplying precursors for biosynthesis
• Acetyl CoA is completely oxidized to carbon dioxide and water, producing NADH and FADH₂

Energy Production from Carbohydrates (Cellular Respiration)

• Metabolism of monosaccharides produces energy
• Excess carbohydrates stored as starch (plants) or glycogen (animals) for later use
• Glucose breakdown during cellular respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

Additional Metabolic Pathways

• Hexose monophosphate shunt: alternative pathway for glucose oxidation, producing NADPH and ribose-5-phosphate
• Gluconeogenesis: biosynthetic pathway producing glucose from non-carbohydrate precursors
• Glycogenesis: pathway for synthesizing glycogen from glucose
• Glycogenolysis: defines the pathway for glycogen breakdown

How Organisms Obtain Energy

• Stepwise oxidation (controlled) of sugars in cells produces energy gradually; compared to the uncontrolled burning of sugar which releases energy all at once as heat
• Enzymes reduce activation energy for reactions
• Total energy released is the same, but stepwise oxidation captures more energy effectively

Energy Metabolism and ATP Synthesis

• Human body uses three types (lipids, proteins, carbohydrates) to create ATP
• Mitochondria, and the cytosolic pathways, are ATP production sites in mammals
• The breakdown (degradation) of lipids, proteins, and carbohydrates creates fatty acids, amino acids, and pyruvate, respectively

Food Molecule Breakdown

• Proteins, lipids, polysaccharides in food are broken down in three stages
• Stage 1: digestion
• Stage 2: cytosol to mitochondrion
• Stage 3: entirely in mitochondrion

Different Cell Types and Fuel Molecules

• Different cell types utilize different fuel molecules
• Red blood cells primarily use glucose; converting it to lactate
• Brain uses glucose and ketone bodies
• Adipose tissue uses fatty acids and glucose
• Liver primarily uses fatty acid oxidation
• Muscle cells use fatty acids, glucose, and amino acids

Oxidation Pathways and Cardiac Muscle

• Oxidation pathways for fatty acids, amino acids, and glucose converge into the TCA cycle in the mitochondria
• During fasting, cardiac muscle primarily uses fatty acids for ATP
• Skeletal muscle during rest also uses fatty acids, but glucose oxidation surpasses fatty acid oxidation with increased exercise intensity

Adipose Tissue, Liver, and Other Organs

• Adipose tissue stores body fat and during fasting, it's the source of fatty acids
• Muscle and adipose tissues also use glucose but primarily at the absorptive stage

###Significance and Role of Glycolysis

• Glycolysis is the major pathway for glucose catabolism in the cytoplasm of all biological tissues. This process generates energy in the form of ATP, crucial for vital cellular functions
• The majority of carbon flux in most cells occurs through glycolysis.
• Plants with modified tissues for storing starch (like potato tubers) and plants adapted for inundated water conditions (like water cress) derive much of their energy from glycolysis

This quiz explores the various energy sources utilized by different muscle and tissue types during various metabolic states. It covers key pathways, substrates, and enzymes involved in energy production and utilization within the body. Test your knowledge on muscle cell metabolism and the role of different nutrients in energy conversion.