CHAPTER 9 ENERGY METABOLISM

LEARNING OUTCOMES Explain the differences among metabolism, catabolism and anabolism Describe aerobic and anaerobic metabolism of glucose Illustrate how energy is extracted from glucose, fatty acids, amino acids, and alcohol using metabolic pathways, such as glycolysis, beta oxidation, the citric acid cycle, and the electron transport system Describe the role that acetyl Co-A plays in cell metabolism 2

LEARNING OUTCOMES Identify the conditions that lead to ketogenesis and it’s importance in survival during fasting Describe the process of gluconeogenesis Compare the fate of energy from macronutrients during the fed and fasted state 3

ENERGY METABOLISM All the macronutrients (CHO, FAT, PRO) and EtOH provide energy, but not in the form our bodies can use. What we will learn today is how we change the energy from the food form you the form we can use. We need the micronutrients to help out 4

5 ANABOLIC OR CATABOLIC- IT MUST BE ONE OF THE TW0 Anabolic pathways use small, simpler compound to build larger, more complex compounds. Catabolic pathways Breakdown compounds Into smaller units.

6 ENERGY FOR THE CELL Why do we need energy? Contract muscles (cardiac, smooth, skeletal) Conducting nerve impulses Pumping ions (active diffusion) Heat is a byproduct of catabolism- lucky for us!

ENERGY FOR THE CELL Adenosine tri phosphate (ATP) The only source of energy the cell can use. It is derived from catabolic reactions Adenosine di phosphate (ADP) Cells break high phosphate bond from ATP Adenosine mono phosphate (AMP) Hydrolysis of ADP used when ATP is in short supply 7

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9 ADENOSINE TRIPHOSPHATE

10 ADENOSINE TRIPHOSPHATE Hydrolysis of these high-energy bonds breaks the bond and release energy.

WHERE DOES THIS ATP COME FROM? ATP is made from ADP and Pi. Adding to Pi to the ADP involves transferring energy from energy- yielding compounds (CHO, FAT, PRO and EtOH), The reactions that enable this to happen are called oxidation-reduction reactions. 11

OXIDATION-REDUCTION Oxidized Loses electrons by gaining oxygen or losing hydrogen. Reduced Gains electrons by losing oxygen or gaining hydrogen. Electrons are the currency that are passed around to make energy for the cell. 12

CARBOHYDRATES Aerobic and Anaerobic pathways are used to make energy. When oxygen is present our bodies can make ATPs. Our bodies can still make ATP when there is no oxygen available but only 2 ATPs are produced for every molecule of glucose. 13

ATP PRODUCTION VIA CARBOHYDRATES (AEROBIC) 1.Glycolysis 2.Synthesis of acetyl CoA 3.Citric Acid Cycle (CAC) Acetyl CoA enters cycle producing ATP 4.The byproducts from steps 1-3 are used in a series of oxidation reduction reactions in the mitochondria of cells, this is where most ATP is produced: The electron transport chain

ATP PRODUCTION VIA CARBOHYDRATES (AEROBIC) Step 1 Glycolysis- “breaking down glucose” This happens in the cytoplasm of the cell. Pyruvate is produced from glucose. Depends on B vitamins 15

Step 2 Now we are in the mitochondria. Pyruvate is oxidized (loses electrons) and forms Acetyl-CoA and NADH +2H ATP PRODUCTION VIA CARBOHYDRATES (AEROBIC)

Step 3- The Citric Acid Cycle (we’re still in the mitochondria). Acetyl-CoA enters the citric acid cycle. In this cycle ATP is produced along NADH + H + and FADH 2 17 ATP PRODUCTION VIA CARBOHYDRATES (AEROBIC)

CITRIC ACID CYCLE 18

Step 4- The Electron Transport Chain. These byproducts (NADH + H + and FADH 2 ) that have been made in step 1-3 now enter the electron transport chain and are oxidized. These reactions account for most of the ATP produced and require oxygen. 19 ATP PRODUCTION VIA CARBOHYDRATES (AEROBIC)

ELECTRON TRANSPORT SYSTEM Final pathway of aerobic respiration- makes almost 90% of ATP produced from catabolism of glucose Passage of electrons along a series of electron carriers (oxygen is waiting at the end to accept the electrons) Minerals involved Copper Iron 20

Occurs in cells with no mitochondria or cells that utilize it when there is no oxygen Pyruvate is converted to lactate (instead of Acetyl- CoA) Lactate is picked up the blood and delivered to the liver Liver synthesizes compounds used in aerobic metabolism from lactate 21 ATP PRODUCTION VIA CARBOHYDRATES (ANAEROBIC)

ATP PRODUCTION VIA FATS 1. Lipolysis Triglycerides broken down into fatty acids and glycerol (this happens in the GI tract). These triglycerides come from the foods we eat or from our fat stores (body fat). 22

ATP PRODUCTION VIA FATS 2.Fatty Acid Oxidation (fatty acids lose electrons) - Takes place in mitochondria -Carnitine shuttles fatty acids from cytosol into mitochondria -In the mitochondria the fatty acids are converted to Acetyl CoA. NADH + H + and FADH 2 are also produced. 23

ATP PRODUCTION VIA FATS 3. Acetyl CoA, NADH + H + and FADH 2 enter the Citric Acid cycle and under co the same process that the Acetyl CoA, NADH + H + and FADH 2 derived from carbohydrates goes through. One molecule of glucose can provide ATPs. One 16-cardon fatty acid can produce 106 ATPs. 24

CITRIC ACID CYCLE 25

FAT METABOLISM Carbohydrates aid fat metabolism by providing enough of key substrates to keep the citric acid cycle going. If there are not enough carbohydrates (glucose molecules) around to keep the citric acid cycle going- fat metabolism cannot function normally. “Fat burns in the flame of carbohydrate.” 26

FAT METABOLISM If the fatty acids cannot enter the citric acid cylce the cannot be completely broken down and form Ketones. Eventually our body can turn these ketones into Acetyl-CoA which can then finally enter the citric acid cycle. This process is called ketogenesis Ketosis in Diabetes Mellitus Ketosis in semistarvation or fasting or very low/no carbohydrate diets. 27

PROTEIN METABOLISM Proteins from food are broken down in to amino acids (there are 20 amino acids) Energy metabolism occurs mostly in the liver (some amino acids are metabolized in muscle tissue). 28

PROTEIN METABOLISM Step 1 Deamination Lose the amine group from the amino acid Requires Vitamin B-6 Carbon skeleton is left to enter CAC These amino groups are Converted to ammonia (toxic) Excreted in the urine 29

PROTEIN METABOLISM The 20 amino acids can fall into two categories: Glucogenic Amino Acid If the carbon skeleton can enter CAC directly or by forming pyruvate –these carbons can eventually become parts of glucose Ketogenic Amino Acid If carbon skeleton can become acetyl CoA, the carbon skeletons do NOT become glucose 30

ALCOHOL METABOLISM Alcohol (EtOH) is 1.The enzyme alcohol dehydrogenase converts EtOH to acetaldehyde and NADH + H + 2.Acetaldehyde is converted to acetyl-CoA which enters the CAC. 31

REGULATION OF ENERGY METABOLISM ATP Concentrations High ATP Anabolic reactions High ADP Catabolic reactions Enzymes (ex. High protein diet increases synthesis of enzymes needed for amino acid catabolism) Hormones (ex. Low insulin would promote gluconeogenesis) Vitamins and Minerals (many needed for metabolic pathways to operate) 32

FASTING AND FEASTING Fasting encourages: Glycogen breakdown Fat breakdown Gluconeogenesis Synthesis of ketone bodies Feasting encourages: Glycogen synthesis Fat synthesis Protein synthesis Urea synthesis 33