Energy MetabolismEnergy Metabolism

IntroductionIntroduction

• Energy• Heat, mechanical, electrical, chemical

• Photosynthesis• Metabolism

• Release of energy, water, and carbon dioxide

Chemical Reactions in the Chemical Reactions in the BodyBody

• Energy metabolism• How body obtains & uses energy from food

• Cells• Liver cells

• Anabolism • Requires energy

• Catabolism• Releases energy

A Typical CellA Typical Cell

Anabolic and Catabolic Anabolic and Catabolic Reactions ComparedReactions Compared

Chemical Reactions in the Chemical Reactions in the BodyBody

• Transfer of energy in reactions – ATP • Released during breakdown of glucose, fatty

acids, and amino acids

• Form of phosphate groups• Negative charge – vulnerable to hydrolysis

• Provides energy for all cell activities• Coupled reactions

• Efficiency• Heat loss

ATP (Adenosine Triphosphate)

Capture and Release of Energy Capture and Release of Energy by ATPby ATP

Chemical Reactions in the Chemical Reactions in the BodyBody

• Enzymes • Facilitators of metabolic reactions

• Coenzymes• Organic• Associate with enzymes

• Without coenzyme, an enzyme cannot function

Breaking Down Nutrients for Breaking Down Nutrients for EnergyEnergy

• 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 Breaking Down Nutrients for EnergyEnergy

• 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

Simplified Overview of Energy-Simplified Overview of Energy-Yielding PathwaysYielding Pathways

Breaking Down Nutrients for Breaking Down Nutrients for Energy – Glucose 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 Breaking Down Nutrients for Energy – Glucose Energy – Glucose

• Pyruvate’s options• Quick energy needs – anaerobic

• Pyruvate to lactate

• Slower energy needs – aerobic• Pyruvate to acetyl CoA

Breaking Down Nutrients for Breaking Down Nutrients for Energy – Glucose 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

Pyruvate-to-Lactate Pyruvate-to-Lactate

Breaking Down Nutrients for Breaking Down Nutrients for Energy – Glucose 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

• Acetyl CoA pathways

Pyruvate-Acetyl CoA Pyruvate-Acetyl CoA

The Paths of Pyruvate and The Paths of Pyruvate and Acetyl CoA Acetyl CoA

Glucose Enters the Energy Glucose Enters the Energy Pathway Pathway

Breaking Down Nutrients for Breaking Down Nutrients for Energy – Glycerol & Fatty Acids Energy – Glycerol & 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

Fatty Acids-to-Acetyl CoA Fatty Acids-to-Acetyl CoA

Fats Enter the Energy Pathway Fats Enter the Energy Pathway

Breaking Down Nutrients for Breaking Down Nutrients for Energy – Amino AcidsEnergy – 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

Amino Acids Enter the Energy Amino Acids Enter the Energy PathwayPathway

Review of Energy-Yielding Nutrient Endpoints

Final Steps of Energy Final Steps of Energy MetabolismMetabolism

• 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

A Mitochondria

Final Steps of Energy Final Steps of Energy MetabolismMetabolism

• Electron transport chain• Captures energy 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

Electron Transport Chain and Electron Transport Chain and ATP SynthesisATP Synthesis

Final Steps of Energy Metabolism

• kCalorie-per-gram secret• Fat provides most energy per gram

• Carbon-hydrogen bonds • More ATP = more kcalories

Feasting – Excess Energy Feasting – Excess Energy

• Metabolism favors fat formation• Regardless of excess from protein, fat, or

carbohydrates• Excess protein• Excess carbohydrate

• Excess fat – most direct and efficient conversion

• Fuel mix

Transition from Feasting to Transition from Feasting to Fasting Fasting

• Glucose, glycerol, and fatty acids are used then stored• Fasting state draws on these stores

• Glycogen and fat are released

• Basal metabolism • Fasting versus starving

Feasting and Fasting Feasting and Fasting

Fasting – Inadequate EnergyFasting – Inadequate Energy

• Carbohydrate, fat, and protein are all eventually used for energy

• Begin with release of glucose and fatty acids• Acetyl CoA

• Low blood glucose levels signal • Fat breakdown• Release of amino acids from muscles

Fasting – Inadequate EnergyFasting – Inadequate Energy

• Adaptation: making glucose• Nervous system and red blood cells

• Amino acids yielding pyruvate

• Breakdown of body proteins

• Adaptation: creating an alternate fuel• Use fat to fuel brain

• Ketone bodies• Slows the rate of body protein breakdown

• Ketosis induces a loss of appetite

Ketone Body FormationKetone Body Formation

Energy Balance – FastingEnergy Balance – Fasting

• Adaptation: conserving energy• Hormones

• Reduces energy output• Supports weight loss but not fat loss• Symptoms of starvation

• Physical symptoms• Psychological symptoms

Low-Carbohydrate DietsLow-Carbohydrate Diets

• Metabolism similar to fasting• Uses glycogen stores first

• Gluconeogenesis when glycogen is depleted• Body tissues used somewhat even when

protein provided in diet

• Urine monitoring• Ketosis

Adverse Side Effects of Low-Carbohydrate, Ketogenic Diets

Alcohol in the Alcohol in the BodyBody

Highlight 7Highlight 7

Alcohol in the BodyAlcohol in the Body

• Potential health benefits

• Alcohols• Glycerol

• Ethanol

• Lipid solvents• Moderation

• Definition of “drink”• Proof

AlcoholAlcohol’s Influence’s Influence

• Alcohol’s special privileges• No digestion

• Quick absorption• Slowing absorption

• Stomach• Alcohol dehydrogenase

• Small intestine• Priority over nutrients

AlcoholAlcohol’s Influence’s Influence

• In the liver• Liver cells

• First to receive alcohol-laden blood

• Alcohol dehydrogenase• Disrupts liver activity

• Can permanently change liver cell structure

• Rate of alcohol metabolism • Acetaldehyde• Acetate

Alcohol MetabolismAlcohol Metabolism

AlcoholAlcohol’s Influence ’s Influence

• In the liver• Niacin coenzyme

• Glycolysis

• TCA cycle

• Electron transport chain

• Development of fatty liver• Damage to central nervous system

• Inflammation of joints

• Amino acid and protein metabolism

Alternate Route for Acetyl Alternate Route for Acetyl CoA: To FatCoA: To Fat

AlcoholAlcohol’s Influence ’s Influence

• In the liver• Immune system functioning

• Alcohol interferes with drug metabolism• Microsomal ethanol-oxidizing system (MEOS)

AlcoholAlcohol’s Influence’s Influence

• In the brain• Sedates inhibitory nerves

• Acts as central nervous system depressant

• Blood alcohol levels and brain responses• Death of liver and brain cells

• Depression of antidiuretic hormone (ADH)• Loss of body water

• Loss of important minerals

AlcoholAlcohol’s Effects on the Brain’s Effects on the Brain

Alcohol Doses & Approximate Blood Level Percentages for Men & Women

Alcohol Blood Levels and Alcohol Blood Levels and Brain ResponsesBrain Responses

AlcoholAlcohol’s Damage’s Damage

• Dehydration• Antidiuretic hormone (ADH)

• Water loss• Loss of minerals

Alcohol’s Damage

• Malnutrition • Can contribute to body fat and weight gain

• 1 ounce of alcohol represents 0.5 ounce of fat

• Central obesity• Substituted energy

• 7 kcalories per gram

• Nutrient displacement• B vitamins

• Wernicke-Korsakoff syndrome

AlcoholAlcohol’s Effects’s Effects

• Short-term effects• Excessive drinking

• Heavy drinking

• Binge drinking

• Long-term effects• Third leading preventable cause of death in

U.S.

• Sobering up

Signs of Alcoholism