BIO 111 Lecture 2: Energy Production and Utilization PDF

BIO 111 GENERAL BIOLOGY I Topic: ENERGY PRODUCTION AND UTILIZATION Prepared by Dr. B.P Olatunji  Food in, energy out? It’s not as simple as that. How do cells meet our bodies’ ever changing energy needs?  #The energy needs of the human body must be fulfilled d...

BIO 111 GENERAL BIOLOGY I Topic: ENERGY PRODUCTION AND UTILIZATION Prepared by Dr. B.P Olatunji  Food in, energy out? It’s not as simple as that. How do cells meet our bodies’ ever changing energy needs?  #The energy needs of the human body must be fulfilled despite the fluctuations in nutrient availability that the body experiences on a daily basis.#  GENERAL OBJECTIVES Students should be able to identify different cells that requires energy Students should be able to explain the process of energy utilization and production of substrates in different cells Students should be able to explain how blood glucose is maintained at a constant level  Metabolism of Carbohydrates Organisms break down carbohydrates to produce energy for cellular processes, and photosynthetic plants produce carbohydrates. Key Points The breakdown of glucose living organisms utilize to produce energy is described by the equation: C6H12O6+6O2→6CO2+6H2O+energy The photosynthetic process plants utilize to synthesize glucose is described by the equation: 6CO2+6H2O+energy→C6H12O6+6O2. Glucose that is consumed is used to make energy in the form of ATP, which is used to perform work and power chemical reactions in the cell. During photosynthesis, plants convert light energy into chemical energy that is used to build molecules of glucose. Key Terms adenosine triphosphate: a multifunctional nucleoside triphosphate used in cells as a coenzyme, often called the “molecular unit of energy currency” in intracellular energy transfer glucose: a simple monosaccharide (sugar) with a molecular formula of C6H12O6; it is a principal source of energy for cellular metabolism  Carbohydrates Carbohydrates are major sources of energy for living organisms. The chief source of carbohydrate in human food is starch, which is the storage form of glucose in plants. Plants may store relatively large amounts of starch within their own cells in time of abundant supply, to be used later by the plant itself when there is a demand for energy production. Glycogen is the glucose storage polysaccharide of animals. It accounts for up to 10% of the mass of the liver and one percent of the mass of the muscle.  Tips on carbohydrates Glycogen is larger and highly branched than amylopectin. By the action of several enzymes, such as α -amylase, α-amylase, amylo α(1→6) glucosidase and α(1→4) glucosidase, starch and glycogen from dietary intake are degraded finally to glucose. Carbohydrate is utilized by cells mainly in the form of glucose.  Tips on carbohydrates The three principal monosaccharides resulting from the digestive processes are glucose, fructose and galactose. Both fructose and galactose are readily converted to glucose by the liver. Pentose sugars such as xylose, arabinose and ribose may be present in the diet, but their fate after absorption is obscure. Since glucose is the compound formed from starch and glycogen, the carbohydrate metabolism commences with this monosaccharide  Metabolism of Carbohydrates Carbohydrates are one of the major forms of energy for animals and plants. Plants build carbohydrates using light energy from the sun (during the process of photosynthesis), while animals eat plants or other animals to obtain carbohydrates. Plants store carbohydrates in long polysaccharides chains called starch, while animals store carbohydrates as the molecule glycogen.  Metabolism of Carbohydrates I. Glycolysis is the sequence of reactions that convert glucose into pyruvate with the concomitant trapping of the energy as ATP. ii. The citric acid cycle It is the final common oxidative pathway for carbohydrates, fats and proteins. It is also a source of precursors for biosynthesis of various biomolecules. The acetyl CoA that enters in this pathway is completely oxidised to carbon dioxide and water with concomitant production of reducing equivalents, namely NADH and FADH2. READ MORE ON The citric acid cycle  Energy Production from Carbohydrates (Cellular Respiration ) The metabolism of any monosaccharide (simple sugar) can produce energy for the cell to use. Excess carbohydrates are stored as starch in plants and as glycogen in animals, ready for metabolism if the energy demands of the organism suddenly increase. The breakdown of glucose during metabolism is call cellular respiration can be described by the equation: C6H12O6+6O2→6CO2+6H2O+energy iii. The hexose monophosphate shunt It is an alternative pathway to the glycolytic pathway and the citric acid cycle for the oxidation of glucose to carbon dioxide and water with the generation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) molecules and ribose 5- phosphate. iv. Gluconeogenesis It is a biosynthetic pathway that generates glucose from non- carbohydrate precursors. v. Glycogenesis: It is a pathway by which glycogen is synthesized from glucose. vi. Glycogenolysis? Define this term. Producing Carbohydrates (Photosynthesis) 6CO2+ 6H2O + energy→ C6H12O6+ 6O2 How Organisms Obtain Energy  Fig 1: Schematic representation of the controlled stepwise oxidation of sugar in a cell, compared with ordinary burning  As shown in fig. 1, In the cell, enzymes catalyze oxidation via a series of small steps in which free energy is transferred in conveniently sized packets to carrier molecules—most often ATP and NADH. At each step, an enzyme controls the reaction by reducing the activation energy barrier that has to be surmounted before the specific reaction can occur. The total free energy released is exactly the same in (A) and (B). But if the sugar was instead oxidized to CO2 and H2O in a single step, as in (B), it would release an amount of energy much larger than could be captured for useful purposes. Fig. 2: Energy Metabolism and ATP Synthesis in Human Cells  The human body uses three types of molecules to yield the necessary energy to drive ATP synthesis: fats, proteins, and carbohydrates. Mitochondria are the main site for ATP synthesis in mammals, although some ATP is also synthesized in the cytoplasm.  Degradation of lipids, proteins, and carbohydrates gives rise to fatty acids, amino acids, and pyruvate respectively. These molecules enter the tricarboxylic acid (TCA) cycle in the mitochondrion to be completely oxidized to CO2 with concomitant reduction of NAD+ and FAD to NADH and FADH2 respectively. The electrons are transported from the reduced coenzymes to O2 in the electron transport system, resulting in ATP synthesis  Food Molecules Are Broken Down in Three Stages to Produce ATP The proteins, lipids, and polysaccharides that make up most of the food we eat. Stage 1 in the enzymatic breakdown of food molecules is therefore digestion. Stage 2 starts in the cytosol and ends in the major energy-converting organelle, the mitochondrion; Stage 3 is entirely confined to the mitochondrion. Fig 3: Three Stages to Produce ATP  Different Cell Types Require Different Fuel Molecules Figure 3: Relationship between the utilization and production of substrates by different cells in the human body.  Relationship between the utilization and production of substrates by different cells in the human body Red blood cells rely on glucose for energy and convert glucose to lactate. The brain uses glucose and ketone bodies for energy. Adipose tissue uses fatty acids and glucose for energy. The liver primarily uses fatty acid oxidation for energy. Muscle cells use fatty acids, glucose, and amino acids as energy source  Indeed, although the oxidation pathways of fatty acids, amino acids, and glucose begin differently, these mechanisms ultimately converge onto a common pathway, the TCA cycle, occurring within the mitochondria. Between meals, cardiac muscle cells meet 90% of their ATP demands by oxidizing fatty acids. Although these proportions may fall to about 60% depending on the nutritional status and the intensity of contractions, fatty acids may be considered the major fuel consumed by cardiac muscle.  Skeletal muscle cells also oxidize lipids. Indeed, fatty acids are the main source of energy in skeletal muscle during rest and mild-intensity exercise. As exercise intensity increases, glucose oxidation surpasses fatty acid oxidation. Other secondary factors that influence the substrate of choice for muscle include exercise duration, gender, and training status.  Since adipose tissue is the storehouse of body fat, one might conclude that, during fasting, the source of fatty acids for adipose tissue cells is their own stock. Skeletal muscle and adipose tissue cells also utilize glucose in significant proportions, but only at the absorptive stage - that is, right after a regular meal.  Other organs that use primarily fatty acid oxidation are the kidney and the liver. The cortex cells of the kidneys need a constant supply of energy for continual blood filtration, and so does the liver to accomplish its important biosynthetic functions. Despite their massive use as fuels, fatty acids are oxidized only in the mitochondria.  Significance of glycolysis Glycolysis is an almost universal central pathway of glucose catabolism occurring in the cytoplasm of all the tissues of biological systems leading to generation of energy in the form of ATP for vital activities. It is the pathway through which the largest flux of carbon occurs in most cells. Some plant tissues which are modified for the storage of starch such as potato tubers and some plants adapted to growth in inundated water such as water cress derive most of their energy from glycolysis  In plants, glycolysis is the key metabolic component of the respiratory process, which generates energy in the form of ATP. Many types of anaerobic microorganisms are entirely dependent on glycolysis Mammalian tissues such as renal medulla and brain solely dependent on glycolysis for major sources of metabolic energy THANK YOU