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

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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

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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

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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 compoundsInto smaller units.

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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

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ADENOSINE TRIPHOSPHATE

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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.

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OXIDATION-REDUCTION

OxidizedLoses electrons by gaining oxygen or losing hydrogen.

ReducedGains electrons by losing oxygen or gaining hydrogen.

Electrons are the currency that are passed around to make energy for the cell.

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CARBOHYDRATES

Aerobic and Anaerobic pathways are used to make energy. When oxygen is present our

bodies can make 30-32 ATPs. Our bodies can still make ATP when there is no oxygen

available but only 2 ATPs are produced for every molecule of glucose.

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ATP PRODUCTION VIA CARBOHYDRATES (AEROBIC)

1. Glycolysis2. Synthesis of acetyl CoA3. Citric Acid Cycle (CAC)

• Acetyl CoA enters cycle producing ATP4. 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 1Glycolysis- “breaking down glucose”This happens in the cytoplasm of the cell. Pyruvate is produced from glucose.

Depends on B vitamins

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Step 2Now we are in the mitochondria.

Pyruvate is oxidized (loses electrons) and forms Acetyl-CoA andNADH +2H+.

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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 FADH2

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ATP PRODUCTION VIA CARBOHYDRATES (AEROBIC)

CITRIC ACID CYCLE

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Step 4- The Electron Transport Chain. These byproducts (NADH + H+ and FADH2) 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.

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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

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• 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

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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).

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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 FADH2 are also produced.

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ATP PRODUCTION VIA FATS

3. Acetyl CoA, NADH + H+ and FADH2 enter the Citric Acid cycle and under co the same process that the Acetyl CoA, NADH + H+ and FADH2 derived from carbohydrates goes through.

One molecule of glucose can provide 30-22 ATPs. One 16-cardon fatty acid can produce 106 ATPs.

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CITRIC ACID CYCLE

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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.”

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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.

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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).

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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

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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

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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.

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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)

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FASTING AND FEASTING

• Fasting encourages:• Glycogen breakdown• Fat breakdown• Gluconeogenesis• Synthesis of ketone bodies

• Feasting encourages:• Glycogen synthesis• Fat synthesis• Protein synthesis• Urea synthesis

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