KIN 211 Metabolism

The sum total of all chemical reactions that go on in the living cells. Energy Metabolism-the reactions by which the body obtains energy from food.

Two Categories of Metabolism Metabolism is usually divided into two categories. – Catabolism – Anabolism

Anabolism Anabolism- when small molecules are used to build larger compounds. Examples: – Glucose to Glycogen – Glycerol and Fatty Acids to Triglycerides – Amino Acids to Proteins – Refer to Figure 7-2.

Catabolism Breaking down of compounds to release energy. – Examples: Glycogen to Glucose to Energy Triglycerides to Glycerol and Fatty Acids to Energy Protein to Amino Acids to Energy

ATP (Adenosine Triphosphate) body uses a high energy compound in which to trap energy released from glucose, glycerol, fatty acids, and amino acids. The body converts chemical energy of food to the chemical energy of ATP at about 50% efficiency.

Helpers in Metabolic Reactions Enzymes and co-enzymes are used as co- workers in metabolic reactions. Several B vitamins act as co-enzymes in the process of energy metabolism.

Following Digestion and Absorption of Nutrients After the body has broken down the energy units and absorbed into the bloodstream, these energy nutrients can be used to fuel the body with energy. The body turns to carbohydrates and fats primarily to provide the energy needs, while protein is used for building body compounds.

Carbohydrate Metabolism The first pathway glucose takes in order to yield energy is called Glycolysis: – The 6 carbon glucose is converted into other 6 carbon compounds and eventually is split in half. The results is two three-carbon compounds called pyruvate.

Glycolosis Is reversable, anaerobic, and occurs in the cytosole of the cells.

Fate of Pyruvate Pyruvate may enter either an anaerobic or aerobic pathway: – Anaerobic: energy is needed quickly (in the absence of sufficient oxygen), pyruvate is converted to lactate. – In high intensity work, the body uses lactate to provide energy. – Lactate is eventually transported from the muscles to the liver. The liver then uses it to produce glucose, which can be returned to the muscle. This process if called the Cori Cycle.

Fate of Pyruvate Aerobic: – If the cells need energy and enough oxygen is available, pyruvate then enters the mitochondria of the cells. – The three-carbon pyruvate drops off a carbon group (COOH), leaving a two-carbon compound. – The two-carbon compound combines with a molecule of CoA, resulting in Acetyl CoA. Refer to Figure 7-7.

Pyruvate to Acetyl CoA This step is irreversable. Acetyl CoA has two main functions: – Making Fats(when ATP’s are in abundance) – Generate ATP(When the body needs ATP, the acetyl CoA proceeds to the TCA cycle.

TCA Cycle Tricarboxylic Acid Cycle Occurs in the Mitochondria of the Cells Oxaloacetate- a 4-carbon compound, carbohydrate intermediate. Oxaloacetate can be made from either pyruvate (from glucose) or amino acids, but cannot be made from fat.

Fate of Oxaloacetate As oxaloacetate enters the TCA cycle, it picks up Acetyl CoA, then drops off a carbon, then another. (These carbons mix with oxygen, form carbon dioxide and are breathed out) and then goes back to get another acetyl CoA. When the acetyl CoA breaks down to carbon dioxide, hydrogen atoms are removed, and each turn of the TCA cycle releases 8 electrons.

Coenzymes: B Vitamins and The Electron Transport Chain The coenzymes then pick up the hydrogen atoms and their electrons and transfer them to the electron transport chain. Electron Transport Chain- a series of proteins that serve as electron carriers.

Results of The Electron Transport Chain Oxygen combines with hydrogen and forms water Energy is trapped in the high energy bonds of ATP: ATP then enters the cyroplasm of the cells and is used for energy. Refer to Fiber 7-19

Where Fat and Amino Acids Enter the Energy Metabolism Pathway Refer to Figure 7-21

Feasting and Fasting In a state of feasting when we eat too much, the body will allow fat formation, whether the calories come from carbohydrates, protein or fat.

Excess Carbohydrates Carbohydrates are first converted into glycogen, which has limited space. Excess glucose is then converted into fat. Excess glucose can then contribute to obesity.

Excess Fat Excess fat moves efficiently into the body’s fat stores, contributing to obesity.

Excess Protein Remember that the body cannot grow extra muscles simply by eating extra protein. When a person eats too much protein, the body will first replace daily losses. The remaining protein is deaminated and the remaining carbons are made into fatty acids, then stored at triglycerides in the adipose tissues. Excess protein builds fat in the body.

Fasting During fasting at some point, carbohydrates, protein and fat is all used as energy.

Fast Begins The body will turn to glucose from the stored glycogen. Cells of the nervous system and red blood cells need glucose for energy. Red Blood cells do not contain a mitochondria (Where energy is extracted from fatty acids, ketone bodies, or oxidative phosphorylation).

What happens to Protein? Remember that the brain and red blood cells require glucose for energy. Fatty Acids cannot be made into glucose, while amino acids that yield pyruvate can be used to make glucose. The breakdown of body protein is an expensive way to make glucose, and in the first days of the fast the body will use protein to make about 90 percent of the needed glucose. The muscles begin to atrophy quickly and continued fasting will eventually result in death.

Fats and Ketosis The body will eventually find a way to use fat to fuel the brain in an emergency fasting state. The body will begin to combine fragments of acetyl CoA (from fatty acids) to produce ketone bodies.

Ketosis Ketone body production continues to rise, until they are meeting most of energy needs of the nervous system. Many areas of the brain will continue to rely on glucose to function. The body will still turn to body proteins to make this glucose. Elevated ketones results in an increase of the PH of the blood, making it very acidic.

The End