2 energy metabolism presentation1 final nut &fitness

2-Energy Metabolism During Rest and Exercise

Nutrition and Fitness semester V

Dr. Siham Gritly

Dr. Siham Gritly

Human cell

Dr. Siham Gritly

Definitions related to the subject

• -Adenosine Triphosphate (ATP), a chemical compound found in all cells that store energy

• *ATP or adenosine tri-phosphate is intermediary compound that has the ability to enter in many reactions. it is nucleotide compound composed of adenine (nitrogen base), ribose (pentose sugar) and three phosphate radicals.

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• -Adenosine Diphosphate ADP, a nucleotide involved in energy metabolism it is produced by hydrolysis of ATP and converted back to ATP by the process of oxidative phosphrylation

• -Creatine Phosphate CP, an important storage form of high energy phosphate in muscle cells

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Objective; By the end of this lecture students should be understand the following terms;

• glycolysis, citric acid cycle, oxidative phospholylation

• (electron transport system)• The ATP-CP system (phosphagen)

• Glycogenolysis

• Glycogenesis

• Gluconeogenesis

• Pentose phosphate pathway.

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Energy in nutrition

• *In nutrition, energy deals with chemical energy that locked in food staff by chemical bonding present in nutrients. energy is derived from energy producing nutrients CHO, fats and proteins.

• *All living cells need energy to continue living. The main source of energy derived from solar energy or sun energy. Human body obtains energy by indirect way from the sun through the process of photosynthesis.

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Uses of energy

• 1-muscular secretion • 2-secretion of the glands • 3-synthesis of new substances • 4-regulation of body temperature • 5-absorption of food from gastro-intestinal

tract • 6-for the basal metabolism e.g. heart beat,

respiration etc.

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Sources of energy (ATP)

• Sources of ATP

• 1- glycolysis,

• 2- citric acid cycle • 3-oxidative phospholylation (electron

transport system)

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1-Glycolysis pathway;

• *Glycolysis is the process of energy releasing from glucose molecules in cytoplasm of cells. in the cytoplasm glucose bind with 6 phosphate radicals this occur by the action of specific enzymes.

• *Glycolysis is splitting of glucose molecule to form 2 molecules of pyruvic acid (pyruvate). This process occurs by 10 steps of chemical reactions, each reaction is catalysed by one specific protein enzyme. It has 2 phases in the first phase energy is needed and the second phase energy is released (ATP),

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• *Glycolysis also define as; the net formation of 2 high energy phosphate result from formation of lactate or lactic acid from one molecule of glucose under an-aerobic condition.

• *Glucose---------oxidation-------------2lactic acid (the

end product of glycolysis under anaerobic condition) or

• *pyruvate (under aerobic condition) + 2ATP (net

formation of glucose oxidation).

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• *pyruvic acid is the second main phase or step in glycolysis process for production of ATP, then enter the mitochondria (power house of the cell)for total oxidation of glucose molecules to water, carbon dioxide and energy.

• *in the fist phase of glycolysis energy is required. energy obtained directly from the chemical compound ATP

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Glycolysis is a central pathway are important part of glucose metabolism because;

• -It produces large amount of energy,

• -occur in all cells,

• -common pathway in breaking down all macro-nutrients (proteins, fats and carbohydrates)

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Glycolysis Pathway

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2-Citric acid cycle;

• *It is known also by Kerb's cycle or tri-carboxylic acid cycle. it represent the second and final process in glucose metabolism. The cycle is discovered by kerb in 1937.

• *Under anaerobic condition mainly in muscle cells, pyruvic acid is converted into lactic acid.

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• *Under aerobic conditions, pyruvic acid is oxidized through kerb's or tri-carboxylic acid cycle in the mitochondria of the cell to energy, carbon dioxide and water.

• *kerb's cycle is a series of reactions in the Mitochondria that bring about the catabolism of acetyl residues, liberating hydrogen equivalent (2H) which on oxidation lead to the release of most of the free energy of tissue fuels. The acetyl residues are in the form of acetyl Co-enzyme A (active acetate).

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Citric acid cycle

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• *the cycle is the major route for the generation of ATP and is located in the matrix of mitochondria adjacent to the enzymes of respiratory chain.

• *It is the final pathway for oxidation of glucose, lipids and protein.

• *It catalyzed the combination of their common metabolite----acetyl Co-enzyme A with oxaloacetate to form citrate by series of dehydrogenation and decarboxylation

• *citrate or citric acid is degraded (break down) releasing

reducing equivalent (energy in the form of H molecules) and 2 carbon dioxide and regenerating oxaloacetate

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3-Electron transport system

• Electron transport chains;

• *are the cellular mechanisms used for extracting energy through redox (reduction –oxidation ) reactions, such as the oxidation of sugars (glucose to water, carbon dioxide and ATP) during the process of cellular respiration in mitochondria (Kerb cycle).

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• *In a simple words it is the oxidation of glucose (C6H12O6) in the human body through a series of complex electron transfer processes (transfer of electrons between spaces) by specific electrons receptors NAD and FAD.

• -Electron transport chains are redox reactions that is; that transfer electrons from an electron donor (NADH) to an electron acceptor (O2) with the transfer of H ions (proton) across a cell membrane releasing energy.

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Electron transport system

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• Reduced electron carriers NADH & FADH2 reduce oxygen to water via the electron transport chain.

• The energy released is used to set up a proton gradient

across the inner mitochondrial membrane.

• The protons flow down this concentration gradient back

across the inner mitochondrial membrane through the ATPase .The energy released is used to generate ATP.

• The citric acid cycle and fatty acid oxidation supply NADH

and FADH2 for production of more through electron

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Glycogenesis

• *Glycogenesis is the formation of glycogen from glucose. Glycogen synthesize is depending on the demand for glucose and ATP (energy).

• *If both are present in relatively high amounts, then the excess of insulin promotes the glucose conversion into glycogen for storage in liver and muscle cells.

• *Glycogen is a large polymer of glucose it is the storage form of glucose. Several enzymes involved in conversions of extra glucose to glycogen

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glucose after absorption can be used immediately for release of energy to the cell or it can be stored in the form of glycogen

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Glycogenolysis

• Glycogenolysis• *is the process of breakdown of glycogen to re-form

glucose in the cells

• *glycogen stored in the liver and muscles, is

converted first to glucose-1- phosphate and then into glucose-6-phosphate.

• *Two hormones which control glycogenolysis are a

peptide, glucagon from the pancreas and epinephrine from the adrenal glands.

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• *Glucagon is released from the pancreas in response to low blood glucose and epinephrine is released in response to a threat or stress.

• Both hormones act upon enzymes to stimulate glycogen phosphorylase to begin glycogenolysis and inhibit glycogen synthetase (to stop glycogenesis)

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• *In the next step the phosphate is moved to the C-6 position to give glucose 6-phosphate, a cross road compound or intermediate compound.

• *Glucose-6-phosphate is the first step of the glycolysis pathway if glycogen is the carbohydrate source and further energy is needed. If energy is not immediately needed, the glucose-6-phosphate is converted to glucose for distribution in the blood to various cells such as brain cells

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Glycogenolysis; break down of glycogen to release glucose

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Gluconeogenesis

• *Gluconeogenesis is the process or mechanisms of synthesizing glucose from non-carbohydrate sources.

• *The starting point of gluconeogenesis is pyruvic acid, although oxaloacetic acid and dihydroxyacetone phosphate also provide entry points.

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• * Lactic acid, some amino acids from protein and glycerol from fat can be converted into glucose.

• Gluconeogenesis is similar but not the exact reverse of glycolysis, some of the steps are the identical in reverse direction and three of them are new ones

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Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate sources

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• Energy and Exercises

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Energy and Exercises

• The energy needs of endurance athletes are high. Every athlete’s calorie needs are different mainly depend on;-

• - gender,• - age, • -body composition,• -types of training• - daily activities. • During heavy training and racing cycles, extreme

changes in weight should be avoided

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• Younger athletes in light training may need fewer than 1,600 calories per day; larger athletes and those in heavy training may need well over 5,000 calories per day. Calories should come from a variety of sources.

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Energy metabolism in rest and exercise

• in the resting state• energy expenditure varies according to physical

activity among individuals• -in the resting state energy is expended in

mechanical activities necessary to sustain life (respiration, circulation, synthesis, nervous system

• - when body at rest energy used is known as basal energy expenditure (BEE) or resting energy expenditure (REE)

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• -exercise and physical activity, muscle exercise increase heat production of the body and thus increase metabolic rate

• -body size and composition• -daily activity

-metabolic rate MR-is the rate of heat liberation during the chemical reaction (metabolism)

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During heavy exercise and activity energy is derived from;

During heavy exercise

1- ATP present in muscle cells

2-storedd creatine phosphate in the cells

3-anaerobic energy released by glycolytic breakdown of glycogen to lactic acid

4-by oxidative process in the cells (glycolysis)

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1- ATP present in muscle cells

• * ATP is a source of high-energy phosphate present everywhere in the cytoplasm and nucleoplasma of all cells and essentially for all the physiological mechanisms that required energy.

• *ATP is known as energy currency of the cells

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• * Anaerobic energy in the muscle produces energy for short, high-intensity bursts of activity lasting no more than several minutes before the lactic acid build-up reaches a threshold known as the lactate threshold.

• *The lactic acid or anaerobic glycolysis system

converts glycogen of the muscles to glucose. Then, with the action of enzymes glucose is broken down an-aerobically to produce lactic acid;

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• *this process creates enough energy to reform ATP molecules, but due to the detrimental effects of lactic acid and H+ ions building up and causing the pH of the blood to become more acidic,

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2-storedd creatine phosphate in the cells

The ATP-CP system (phosphagen)• *creatine phosphate (CP) is another high

energy rich compound and is considered the reservoir of high energy phosphate. this compound is stored in the body in large quantities than ATP.

• - Creatine phosphate, also known as ATP-PC or ATP-CP system, is the first source of energy used;

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• -The ATP-CP system is related system in muscle cells by using high-energy phosphate bond of creatine phosphate together with ATP

• -it works by forming ATP and then by breaking down a creatine phosphate which creates and which then will reform ATP.

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• This is not used for muscle contraction, but is mainly used for resynthesising ATP and to maintain a constant supply of energy.

• These reactions occur very rapidly and only

last up to high intensity (this only lasts for a short period of time).

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• The ATP-CP energy pathway do not require any oxygen to create ATP. It first uses up any ATP stored in the muscle (about 2-3 seconds) and then it uses creatine phosphate (CP) to resynthesize ATP until the CP runs out (another 6-8 seconds).

• • After the ATP and CP are used the body will

move on to either aerobic or anaerobic metabolism (glycolysis) to continue to create ATP to fuel exercise.

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3-anaerobic energy released by glycolytic breakdown of glycogen to lactic acid

• *During physical activity the energy is met by the presence of ATP

• *Most of extra energy required during strenuous activity derived from anaerobic glycolysis

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• *The anaerobic energy pathway, or glycolysis, creates ATP exclusively from carbohydrates, with lactic acid being a by-product.

• *Anaerobic glycolysis provides energy by the (partial) breakdown of glucose without the need for oxygen.

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4-by oxidative process in the cells (Aerobic glycolysis)

• * Aerobic metabolism is used primarily during moderate exercise, which is generally less intense and can continue for long periods of time.

• *within the cells the nutrients amino acids, fatty acids and glucose react with oxygen (oxidation) to form carbon dioxide, water, pyruvate and energy. Energy produced used to form adenosine tri-phosphate

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• Aerobic metabolism fuels most of the energy needed for long duration activity. It uses oxygen to convert nutrients (carbohydrates, fats, and protein) to ATP.

• This system is a bit slower than the anaerobic

systems because it relies on the circulatory system to transport oxygen to the working muscles before it creates ATP.

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• During exercise, ATP is produced via anaerobic metabolism. With an increase in breathing and heart rate, there is more oxygen available and aerobic metabolism begins and continues until the lactate threshold is reached.

• If this level is exceed, the body can not deliver oxygen quickly enough to generate ATP and anaerobic metabolism kick in again.

• Since this system is short-lived and lactic acid levels rise, the intensity can not be sustained and the athlete will need to decrease intensity to remove lactic acid build-up.

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References

• Sareen Gropper, Jack Smith and James Groff, Advanced Nutrition and Human Metabolism, fifth ed. WADSWORTH

• Melvin H Williams 2010; Nutrition for Health, Fitness and Sport. 9th

ed, McGraw Hill• • Heymsfield, SB.; Baumgartner N.; Richard and Sheau-Fang P. 1999.

Modern Nutrition in Health and Disease; Shils E Maurice, Olson A. James, Shike Moshe and Ross A. Catharine eds. 9th edition

• Guyton, C. Arthur. 1985. Textbook of Medical Physiology. 6th edition, W.B. Company