25 Metabolism and Energetics C h a p t e r PowerPoint® Lecture Slides prepared by Jason LaPres Lone Star College - North Harris Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Metabolism Metabolism is all the chemical reactions that occur in an organism Cellular metabolism Cells break down excess carbohydrates first, then lipids Cells conserve amino acids 40% of the energy released in catabolism is captured in ATP Rest is released as heat

Figure 23.1 An Introduction to Cellular Metabolism

Anabolism Performance of structural maintenance and repairs Support of growth Production of secretions Building of nutrient reserves

Figure 23.2 Metabolic Turnover and Cellular ATP Production

Cells and Mitochondria Cells provide small organic molecules for their mitochondria Mitochondria produce ATP used to perform cellular functions

Figure 23.3 Nutrient Use in Cellular Metabolism

Most cells generate ATP through the breakdown of carbohydrates Glycolysis One molecule of glucose = two pyruvate ions, two ATP, two NADH Aerobic metabolism (cellular respiration) Two pyruvates = 34 ATP The chemical formula for this process is C6H12O6 + 6 O2  6 CO2 + 6 H2O

Glycolysis The breakdown of glucose to pyruvic acid This process requires: Glucose molecules Cytoplasmic enzymes ATP and ADP Inorganic phosphate NAD (nicotinamide adenine dinucleotide) The overall reaction is: Glucose + 2 NAD + 2 ADP + 2Pi  2 Pyruvic acid + 2 NADH + 2 ATP

Figure 23.4 Glycolysis Figure 23.4

Mitochondrial ATP Production (cellular respiration) Pyruvic acid molecules enter mitochondria Broken down completely in TCA cycle Decarboxylation Hydrogen atoms passed to coenzymes Oxidative phosphorylation

Figure 23.5 The TCA Cycle PLAY Animation: TCA cycle Figure 23.5a

Figure 23.5 The TCA Cycle Figure 23.5b

Oxidative phosphorylation and the ETS Requires coenzymes and consumes oxygen Key reactions take place in the electron transport system (ETS) Cytochromes of the ETS pass electrons to oxygen, forming water The basic chemical reaction is: 2 H2 + O2  2 H2O

Figure 23.6 Oxidative Phosphorylation PLAY Animation: Chemiosmosis Figure 23.6a

Figure 23.6 Oxidative Phosphorylation Figure 23.6b

Energy yield of glycolysis and cellular respiration Per molecule of glucose entering these pathways Glycolysis – has a net yield of 2 ATP Electron transport system – yields approximately 28 molecules of ATP TCA cycle – yields 2 molecules of ATP

Figure 23.7 A Summary of the Energy Yield of Aerobic Metabolism

Synthesis of glucose and glycogen Gluconeogenesis Synthesis of glucose from noncarbohydrate precursors Lactic acid, glycerol, amino acids Liver cells synthesis glucose when carbohydrates are depleted Glycogenesis Formation of glycogen Glucose stored in liver and skeletal muscle as glycogen Important energy reserve

Figure 23.8 Carbohydrate Breakdown and Synthesis

Lipid catabolism Lipolysis Lipids broken down into pieces that can be converted into pyruvate Triglycerides are split into glycerol and fatty acids Glycerol enters glycolytic pathways Fatty acids enter the mitochondrion

Lipid catabolism Beta-oxidation Breakdown of fatty acid molecules into 2-carbon fragments Enter the TCA Irreversible Lipids and energy production Cannot provide large amounts in ATP in a short amount of time Used when glucose reserves are limited

Figure 23.9 Beta Oxidation Figure 23.9

Lipid synthesis (lipogenesis) Almost any organic molecule can be used to form glycerol Essential fatty acids cannot be synthesized and must be included in diet Linoleic and linolenic acid

Figure 23.10 Lipid Synthesis

Lipid transport and distribution 5 types of lipoprotein Lipid-protein complex that contains large glycerides and cholesterol Chylomicrons Largest lipoproteins composed primarily of triglycerides Very low-density lipoproteins (VLDLs) Contain triglycerides, phospholipids and cholesterol

Lipid transport and distribution 5 types of lipoprotein (continued) Intermediate-density lipoproteins (IDLs) Contain smaller amounts of triglycerides Low-density lipoproteins (LDLs) Contain mostly cholesterol High-density lipoproteins (HDLs) Equal amounts of lipid and protein

Lipoprotein lipase Enzyme that breaks down complex lipids Found in capillary walls of liver, adipose tissue, skeletal and cardiac muscle Releases fatty acids and monglycerides

Figure 23.11 Lipid Transport and Utilization Figure 23.11a

Figure 23.11 Lipid Transport and Utilization Figure 23.11b

Amino acid catabolism If other sources inadequate, mitochondria can break down amino acids TCA cycle Removal of the amino group (-NH2) Transamination – attaches removed amino group to a keto acid Deamination – removes amino group generating NH4+ Proteins are an impractical source of ATP production

Figure 23.12 Amino Acid Catabolism

Protein synthesis Essential amino acids Cannot be synthesized by the body in adequate supply Nonessential amino acids Can be synthesized by the body via amination Addition of the amino group to a carbon framework

Figure 23.13 Amination Figure 23.13

Figure 23.14 A Summary of the Pathways of Catabolism and Anabolism

Nucleic acid metabolism Nuclear DNA is never catabolized for energy RNA catabolism RNA molecules are routinely broken down and replaced Generally recycled as nucleic acids Can be catabolized to simple sugars and nitrogenous bases Do not contribute significantly to energy reserves

Nucleic acid synthesis Most cells synthesis RNA DNA synthesized only when preparing for division

Homeostasis No one cell of the human body can perform all necessary homeostatic functions Metabolic activities must be coordinated

Body has five metabolic components Liver The focal point for metabolic regulation and control Adipose tissue Stores lipids primarily as triglycerides Skeletal muscle Substantial glycogen reserves

Body has five metabolic components Neural tissue Must be supplied with a reliable supply of glucose Other peripheral tissues Able to metabolize substrates under endocrine control

The absorptive state The period following a meal Nutrients enter the blood as intestinal absorption proceeds Liver closely regulates glucose content of blood Lipemia commonly marks the absorptive state Adipocytes remove fatty acids and glycerol from bloodstream Glucose molecule are catabolized and amino acids are used to build proteins

Figure 23.15 The Absorptive State

The Postabsorptive State From the end of the absorptive state to the next meal Body relies on reserves for energy Liver cells break down glycogen, releasing glucose into blood Liver cells synthesize glucose Lipolysis increases and fatty acids released into blood stream Fatty acids undergo beta oxidation and enter TCA

The Postabsorptive State Amino acids either converted to pyruvate or acetyl-CoA Skeletal muscles metabolize ketone bodies and fatty acids Skeletal muscle glycogen reserves broken down to lactic acid Neural tissue continues to be supplied with glucose

Figure 23.16 The Postabsorptive State

Diet and Nutrition Nutrition Absorption of nutrients from food Balanced diet Contains all the ingredients necessary to maintain homeostasis Prevents malnutrition

Food Food groups and food pyramids Used as guides to avoid malnutrition

Food Groups Six basic food groups of a balance diet arranged in a food pyramid Milk, yogurt and cheese Meat, poultry, fish, dry beans, eggs, and nuts Vegetables Fruits Bread, cereal, rice and pasta Base of pyramid Fats, oils and sweets Top of pyramid

Figure 23.17 The Food Pyramid and Dietary Recommendations

Nitrogen balance N compounds contain nitrogen Amino acids, purines, pyrimidines, creatine, porphyrins Body does not maintain large nitrogen reserves Dietary nitrogen is essential Nitrogen balance is an equalization of absorbed and excreted nitrogen

Minerals Act as co-factors in enzymatic reactions Contribute to osmotic concentrations of body fluids Play a role in transmembrane potentials, action potentials Aid in release of neurotransmitters and muscle contraction Assist in skeletal construction and maintenance Important in gas transport and buffer systems Aid in fluid absorption and waste removal

Vitamins Are needed in very small amounts for a variety of vital body activities Fat soluble Vitamins A, D, E, K Taken in excess can lead to hypervitaminosis Water soluble Not stored in the body Lack of adequate dietary intake = avitaminosis

You should now be familiar with: Why cells need to synthesis new organic components The basic steps in glycolysis, the TCA cycle, and the electron transport chain The energy yield of glycolysis and cellular respiration The pathways involved in lipid, protein and nucleic acid metabolismBMR

You should now be familiar with: The characteristics of the absorptive and postabsorptive metabolic states What constitutes a balanced diet and why such a diet is important