Chapter 7

Introduction Energy Heat Mechanical Electrical Chemical Stored in food and body Metabolism Release of energy(ATP), water, and carbon dioxide

Chemical Reactions in the Body Energy metabolism ways the body obtains & uses energy from food Site of Metabolic rxns Cell (non-stop metabolic work) Liver cells Anabolism [ana= (build) up] Requires energy Catabolism [kata=(break)down] Releases energy

Chemical Reactions in the Body

Transfer of energy in reactions – ATP Released during breakdown of glucose, fatty acids, and amino acids Form of phosphate groups o Negative charge – vulnerable to hydrolysis Provides energy for all cell activities Coupled reactions o Efficiency & Heat loss o 50% from food to ATP; 50% lost as heat

Chemical Reactions in the Body Enzymes Facilitators of metabolic reactions Coenzymes Organic Associate with enzymes Without coenzyme, an enzyme cannot function

Breaking Down Nutrients for Energy Digestion Carbohydrates – glucose (& other monosaccharides) Fats (triglycerides) – glycerol and fatty acids Proteins – amino acids Molecules of glucose, glycerol, amino acids, and fatty acids Catabolism Carbon, nitrogen, oxygen, hydrogen

Breaking Down Nutrients for Energy Two new compounds Pyruvate 3-carbon structure Can be used to make glucose Acetyl CoA 2-carbon structure Cannot be used to make glucose TCA cycle and electron transport chain

Breaking Down Nutrients for Energy – Glucose Glucose-to-pyruvate Glycolysis 2 pyruvate molecules Hydrogen atoms carried to electron transport chain Pyruvate can be converted back to glucose Liver cells and kidneys (to some extent)

Breaking Down Nutrients for Energy – Glucose Pyruvate’s options Quick energy needs – anaerobic Pyruvate-to-lactate Slower energy needs – aerobic Pyruvate-to-acetyl CoA

Breaking Down Nutrients for Energy – Glucose Pyruvate-to-lactate Pyruvate accepts hydrogens Converts pyruvate to lactate Occurs to a limited extent at rest Produces ATP quickly Mitochondrial ability Accumulation of lactate in muscles Effects Cori cycle

Breaking Down Nutrients for Energy – Glucose Pyruvate-to-Acetyl CoA Pyruvate enters mitochondria of cell Carbon removed – becomes carbon dioxide 2-carbon compound joins with CoA becoming acetyl CoA – irreversible

Breaking Down Nutrients for Energy – Glucose Acetyl CoA’s options – 2 functions Synthesize fats Generate ATP through TCA cycle Hydrogens – electron transport chain

Breaking Down Nutrients for Energy – Glucose

Breaking Down Nutrients for Energy – Glycerol and Fatty Acids Glycerol-to-pyruvate Glycerol can be converted Glucose Pyruvate Fatty acids-to-Acetyl CoA Fatty acid oxidation 2-carbon units at a time then join with CoA Hydrogens and electrons carried to electron transport chain

Breaking Down Nutrients for Energy – Amino Acids Deamination of amino acids Amino acids-to-energy Several entry points in energy pathway Converted to pyruvate (glucogenic) Converted to acetyl CoA (ketogenic) Enter TCA cycle directly (glucogenic) Amino acids-to-glucose

Breaking Down Nutrients for Energy – Glucose

Final Steps of Catabolism TCA Cycle Inner compartment of mitochondria Circular path Acetyl CoA Oxaloacetate – made primarily from pyruvate Carbon dioxide release Hydrogen atoms and their electrons Niacin and riboflavin

Final Steps of Catabolism Electron transport chain Energy captures in ATP Series of proteins Electron “carriers” Inner membrane of mitochondria Electrons passed to next carrier Join oxygen at end of chain – water released ATP synthesis

Energy Balance – Feasting Metabolism favors fat formation Regardless of excess from protein, fat, or carbohydrates Dietary fat to body fat is most direct and efficient conversion Carbohydrate and protein have other roles to fulfill before conversion to body fat

Energy Balance – Transition from Feasting to Fasting Glucose, glycerol, and fatty acids are used then stored Fasting state draws on these stores Glycogen and fat are released

Fasting—Inadequate Energy Glucose is needed for the brain and nerve cells. Protein meets glucose needs through amino acids that provide pyruvate. The shift to ketosis occurs when the brain becomes fueled by ketone bodies. Ketones produced when glucose is not available. Ketosis causes a suppression of the appetite. Hormones slow metabolism. Symptoms of Starvation: Muscle wasting. Decreased heart rate, respiratory rate, metabolic rate, and body temperature. Impaired vision, Organ failure, Decreased immunity. Depression, anxiety, and food-related dreams.

Low-Carbohydrate Diets Metabolism similar to fasting Result in changes in metabolism similar to what occurs during fasting. Ketones will be present in the urine when glycogen depletion has occurred. When a dieter returns to a well-balanced diet, the body will retain depleted nutrients.