Ch.3 Energy Systems & Exercise

The purpose of the three energy systems...

(creatine phosphate, anaerobic glycolysis, and oxidative phosphorylation)—is to use chemical energy to re-form ATP, the direct source of energy used by cells in the body.

Explain glycolysis

*Beginning with glucose, two out of the first three reactions require ATP; that is, they require the input of energy for the reaction to proceed. *The complete process of glycolysis involves 18 chemical reactions but only 12 chemical compounds because 6 reactions are repeated or duplicated. 1) Energy and a phosphate group from an ATP is added to glucose to form glucose-6-phosphate (G-6-P) 4) Glucose is a compound that contains six carbon molecules, and in the fourth step it is split into 2 three-carbon molecules 5) After a side step reaction to dihydroxyacetone phosphate (DHAP) the three-carbon molecules are identical, so the remaining reactions of glycolysis are duplicated 6) In the sixth chemical reaction, sufficient energy is released to phosphorylate ADP into ATP. This is one of the reactions that is repeated, so two ATP are produced at this point. In the ninth reaction, the same thing occurs, so two additional ATP are produced 9) The result of this ninth reaction is the production of pyruvate, another important intermediate compound. In anaerobic glycolysis, pyruvate then proceeds through the final chemical reaction to lactate. *Glycolysis produces four ATP, but two ATP are used in the process, so the final (net) ATP production from anaerobic glycolysis is two ATP.

Creatine levels in vegetarians

- Although research is limited in this area, there is some consistent evidence that the total amount of creatine in the muscles of vegetarians is lower than for nonvegetarians - Vegetarians are not creatine deficient (they may be on the lower end of the normal range), but they do have relatively less creatine than nonvegetarians who complement the production of creatine in the body with creatine found in meat and fish.

Creatine Supplementation Recommendations:

- Application is very specific to strength and power activities. - Creatine is not a "magic pill"— it is only effective in conjunction with vigorous training. - Response may be related to initial creatine levels. - Do not use if kidney disease or dysfunction is present. - Supplement dose is typically 3 to 5 grams per day. - Loading dose is typically 20 to 25 grams per day in four to five doses for 5 to 7 days. - Loading is not necessary unless time urgent. - Consume with carbohydrates to enhance uptake. - Be well hydrated. - Document any adverse effects and reevaluate use.

Exercise and fuel usage (increasing intensity)

- As exercise intensity increases, the percentage of kilocalories derived from fat metabolism decreases, and the percentage from carbohydrate oxidation increases but the total fuel used increases overall

Creatine transport and storage

- Creatine is transported in the bloodstream to tissues throughout the body. - Tissues such as skeletal muscle take up creatine from the blood and store it, approximately one-third as creatine (Cr) and two-thirds as creatine phosphate (CrP).

Why is carbohydrate oxidation preferred by the body during exercise?

- Fewer chemical steps are involved in carbohydrate oxidation, and less oxygen consumption is required for the amount of ATP produced, making carbohydrates the preferred fuel source at higher intensities of exercise. - The chronic consumption (that is, over a period of days or weeks) of a high-carbohydrate diet influences the body to rely more heavily on carbohydrate metabolism to a certain degree, even at rest.

Duration can also affect the fuel utilized in moderate to higher exercise intensity if the exercise continues for long periods of time

- If the body is relying predominantly on carbohydrates, eventually the carbohydrate stores are reduced to the point that fat oxidation may become the predominant fuel source.

An athlete's training status also affects the mixture of fuels utilized during exercise.

- Individuals who have engaged in extensive endurance training improve their ability to metabolize fat. - At the same absolute exercise intensity (for example, the same running pace), they will utilize a higher percentage of fat and a lesser percentage of carbohydrate than lesser-trained athletes.

Characteristics of the creatine phosphate energy system

- One chemical step - Catalyzed by CK - Very fast reaction - One ATP per CrP molecule - 5- to 10-second duration - Anaerobic - Fatigue associated with CrP depletion - Predominant energy system in very high-intensity exercise, for example, "power" events

How can our diet influence what our body uses as fuel during exercise?

- The chronic consumption (that is, over a period of days or weeks) of a high-carbohydrate diet influences the body to rely more heavily on carbohydrate metabolism to a certain degree, even at rest. - Consuming a high-carbohydrate meal before exercise can also influence the body to rely slightly more on carbohydrates at the same exercise intensity compared to not eating or fasting before exercise. - Similarly, chronic consumption of a high-fat diet influences the body to rely more on fat oxidation at rest and during low- and moderate-intensity exercise. - Higher intensities of exercise, however, still rely predominantly on carbohydrates.

Electron Transport Chain

- The electron transport chain is yet another series of chemical reactions that take place within the inner membrane of the mitochondria - Electrons are passed along a series of complexes containing compounds that shuttle the electrons down the chain. Oxygen is the final electron acceptor, picking up electrons in the form of hydrogen to form water. - When NAD is the electron carrier, enough energy is released to re-form 2.5 ATP, and when FAD is the electron carrier, the resulting ATP formation is 1.5.

What's a major disadvantage of using glycolysis?

- The major disadvantage of this energy system is the increasing acidity within the muscle cell that occurs when anaerobic glycolysis is used at a high rate, as occurs during moderately high to high-intensity exercise - Because the acidity is a result of a very high rate of metabolism, it is referred to as metabolic acidosis - If this acidosis occurs in exercising muscle, the drop in pH can result in the decrease in activity of key metabolic enzymes and can interfere directly with the process of force production, resulting in muscle fatigue.

Rephosphorylation of Creatine Phosphate from Creatine depends on aerobic metabolism

- The presence of oxygen is not required when CrP is used to replenish ATP. - However, the recovery of CrP from creatine depends on aerobic metabolism in the cell, in a process referred to as the Creatine Shuttle *Creatine molecules can use the energy from ATP produced aerobically in the mitochondria to restore creatine to creatine phosphate --> Once restored, creatine phosphate is ready as a reservoir of energy for high-intensity exercise.

Fats Are Metabolized Aerobically by the Oxidation of Fatty Acids

- The principal fats metabolized for energy in the body are fatty acids containing chains of either 16 or 18 carbons (palmitate and stearate) 1) These fatty acid chains are stored as triglycerides in fat cells (adipocytes) and in other tissues, such as muscle --> lipolysis where triglycerides are broken down into fatty acid chains 2) The fatty acids are then released from the adipocytes into the blood for transportation throughout the body. At this point, they are usually referred to as free fatty acids (FFA). 3) Fatty acids must be bound to a protein in order to be carried in the blood. to tissues like muscle --> Albumin is the most common plasma protein that binds FFA in the circulation. 4) After an activation step that requires the use of ATP, the fatty acids are transported into the mitochondria for aerobic metabolism 5) B-oxidation is a process comprising four chemical steps that occur in the mitochondrial matrix. The overall function of B-oxidation is to remove 2-carbon segments from the fatty acid chains and convert them to acetyl CoA. 6) The process of B-oxidation also results in FAD and NAD picking up electrons, which can be used in the electron transport chain.

Why are people with diabetes prone to ketoacidosis?

- They have trouble metabolizing carbohydrates so their body metabolizes fats - Excessive reliance on fat metabolism results in the production of keto acids. When produced in excess, keto acids can disturb the acid-base balance in the body.

Creatine amounts (food and supplements)

- Those who eat beef and fish consume approximately 1 to 2 g of creatine daily - Creatine can also be consumed as a dietary supplement, usually 3 to 5 g/d - Creatine as a supplement generally is found as creatine monohydrate in a white powdered form, which is mixed with water for consumption.

How does creatine phosphate usage differ from ATP in terms of amount?

- Unlike ATP, CrP can be used to the extent that it will decrease to very low concentrations. *A normal resting level of total creatine (creatine 1 creatine phosphate) in muscle is approximately 120 mmol/kg (millimoles per kilogram of muscle) of which approximately two-thirds, or 80 mmol/kg, is creatine phosphate. - We can't use up all of our ATP b/c it would be really bad for us --> muscle fatigue happens when we are at 70% of ATP levels

Examples of activities where oxidative phosphorylation is the predominant energy system include "aerobic" activities, such as the following:

- Walking - Jogging and distance running - Cycling (longer distances, not sprint cycling) - Swimming (longer distances, not sprints) - Dance aerobics

What happens to lactate in glycolysis?

- When concentrations of lactate are high, lactate can also be converted to pyruvate (b/c pyruvate can be converted to lactate) - When lactate is produced in cells, such as those in exercising muscle, the increase in lactate concentration results in the movement of lactate molecules out of the cell and into the blood. - Once in the blood, lactate molecules can be distributed throughout the body, where they can be taken up by other highly aerobic tissues (for example, heart, liver, kidney) and metabolized aerobically --> The more lactate that needs to be oxidized, the more aerobic metabolism must be increased to accomplish this task. - Highly aerobic tissues in the body (for example, liver, heart muscle, slow-twitch muscle fibers) can take up lactate molecules and use them as a fuel source to produce ATP via aerobic metabolism.

What happens when we use glycogen as a starting product for glycolysis and NOT glucose?

1) If the beginning point of the reaction is glycogen, the pathway skips the first reaction that requires the use of an ATP, and the reaction beginning with glycogen goes directly to glucose-6-phosphate. *glycogenolysis prepares glycogen for aerobic metabolism by producing pyruvate 2) When glycogenolysis (that is the breakdown of glycogen) is used instead of glycolysis (that is, the breakdown of glucose), four ATP are produced, and only one is used in the process, so the final or net ATP production is three ATP *Glycogenolysis is obviously more energetically efficient, and in fact, exercising muscle will generally use stored glycogen in preference to glucose because the energy yield is higher.

What are the phases of the oxidative phosphorylation process?

1) In the first phase, carbohydrates, fats, and proteins are prepared to be metabolized aerobically 2) The second major phase is the Krebs cycle --> produces a very limited amount of ATP directly, so its primary function is to oxidize, or remove electrons from, the compounds produced from the breakdown of carbohydrates, fats, and proteins 3) The electrons removed in the Krebs cycle are used in the final phase, the electron transport chain. Electrons are passed through a series of chemical reactions, which release energy to rephosphorylate ADP into ATP. *As the electrons pass through the electron transport chain, the final electron acceptor is oxygen, making this the aerobic energy system.

If the starting point is glucose, complete aerobic metabolism involves

124 steps, 30 chemical compounds, and 27 enzymes

What do we need ATP for in terms of muscle contraction?

ATP is needed for force production for the muscle and also for the relaxation of the muscle --> failure to replenish ATP in the muscle may result in fatigue and rigor, a persistent contracted state.

Protein metabolism is complex because there are 20 amino acids and a variety of points of entry into the oxidative process

Alanine and isoleucine are amino acids that are readily oxidized, and they are given as examples because each has a slightly different way of being metabolized - Alanine is a 3-carbon amino acid that, when deaminated, can be converted in to a single pyruvate. - Isoleucine, one of the branched chain amino acids, contains six carbons. Each 2-carbon fragment can be converted to acetyl CoA, which can then be oxidized in the Krebs cycle.

Glycolysis is the preferred energy system for exercises lasting how long?

Anaerobic glycolysis is a relatively fast-acting energy system, however, and becomes the preferred or predominant system to supply energy during high-intensity or repeated exercise lasting approximately 1 to 2 minutes.

The Anaerobic Glycolysis Energy System

Anaerobic glycolysis is the process of taking carbohydrate in the body and putting it through a series of chemical reactions that release enough energy to phosphorylate ADP and re-form ATP

How long is the creatine phosphate system?

At very high intensities of exercise, it takes approximately 5 to 10 seconds for CrP in muscle to be depleted and fatigue to occur, so it is said that the duration of the creatine phosphate energy system is approximately 5 to 10 seconds.

Anaerobic Glycolysis

Carbohydrates in the form of glucose are broken down through a series of chemical reactions that result in a net formation of ATP --> lactic acid is producted but is a weak acid so readily dissociates into --> lactate + hydrogen ions

How much ATP does fat oxidation yield?

Complete metabolism of the fatty acid palmitate results in the production of 113 ATP - Even a person with a relatively low percentage of body fat has a large number of kilocalories stored as fatty acids in adipocytes, which are accessible for metabolism - The disadvantages of fat metabolism include the increased number of steps required and the amount of oxygen needed for aerobic metabolism.

Characteristics of 3 Energy Systems

Creatine Phosphate- very fast (speed of action), very small (Amount of ATP replenished), very short (duration of action) Anaerobic Glycolysis- fast (speed of action), small (Amount of ATP replenished), short (duration of action) Oxidative Phosphorylation- very slow (speed of action), large (amount of ATP replenished), very long (duration of action) **A better analogy for the operation of the three energy systems might be a series of dimmer switches. All three are "on" all the time, but in certain situations, one of the systems may be "turned up" more than the other two.

What is creatine? Where can you get it?

Creatine is an amine, a nitrogen-containing compound similar to a protein, constructed from the amino acids arginine, glycine, and methionine - It can be either consumed in the diet via food or supplements or produced by the body ex: found in fish or beef

Explain the creatine phosphate energy system

Creatine phosphate + ADP --> Creatine kinase is the enzyme used for the reaction --> ATP + Creatine - If ATP concentrations in a muscle cell start to decline, the drop in ATP and the concomitant rise in ADP in the cell result in an increase in the activity of CK, allowing the reaction to proceed even faster. - The reaction does not depend on the presence of oxygen, so this energy system is considered to be one of the anaerobic ("without oxygen") energy systems - Each molecule of CrP can rephosphorylate 1 molecule of ADP to ATP, so the ratio of ATP energy produced is 1:1.

With intense exercise, what about creatine changes in terms of amount?

Creatine refers to creatine and the form creatine phosphate - With intense exercise, the amount of total creatine doesn't change in the muscle, but creatine phosphate can be reduced to very low levels in as little as 10 seconds. - The term depletion is used, even though the muscle creatine levels do not actually drop to zero

Creatine made in the body

Even if creatine is not consumed directly in the diet, the liver and kidneys can synthesize it in adequate amounts if the amino acids arginine, glycine, and methionine are present in sufficient quantities *A creatine deficiency in humans would be extremely rare.

What happens if we have excess creatine?

Excess creatine is filtered by the kidneys and is excreted as the chemical compound creatinine. - The body's "turnover" of creatine is approximately 2 g per day (an average nonvegetarian who does not use creatine supplements will consume and/or synthesize approximately 2 g of creatine daily, and the body will excrete approximately the same amount as creatinine)

Excessive reliance on fat metabolism results in what?

Excessive reliance on fat metabolism results in the production of keto acids. When produced in excess, keto acids can disturb the acid-base balance in the body. - An example of this can be seen in those who have difficulty metabolizing carbohydrates

At rest what is the preferred fuel source?

Fat b/c even a person with a relatively low percentage of body fat has ample fat stores, and fat oxidation has a very high ATP yield. - Because the rate of energy expenditure at rest is low, and there is no need to replace ATP quickly, there is sufficient time for lipolysis, fat mobilization, and -oxidation. - The body does not rely 100 percent on fat oxidation at rest, however. Some tissues, such as brain cells, rely on carbohydrates (glucose) as their primary source of fuel - Under normal circumstances, at rest, fat is generally the predominant fuel source, making up approximately 85 percent of energy expenditure, whereas carbohydrates make up the balance (15 percent).

How does respiration differ with carbs, fats and proteins

It differs from where it starts but after acetyl CoA is formed, the steps of the Krebs cycle and the electron transport chain are the same regardless of whether the original source was carbohydrates, proteins, or fats.

What other ways can our body make use of lactate?

Liver- Cori cycle; enzymes convert lactate to make glucose --> glucose is released into the blood to maintain blood glucose concentration and provides carbs to other cells in the body

What are examples of exercises that use the anaerobic glycolysis are the primary energy system?

Long or repeated sprints - Long sprints such as the 400-meter sprint in track - Repeated high-intensity sprints such as the intermittent sprints by a soccer or basketball player - Repeated high-force activities such as 10 to 15 repetitions of weight lifting - Regular, repeated intervals such as 50- to 100-meter swimming intervals

Oxidative phosphorylation is used to fuel what type of physical activity?

Oxidative phosphorylation is the predominant energy system used at rest and to support low- to moderate-intensity exercise - Oxidative Phosphorylation Is the predominant energy System for Endurance Exercise, such as Marathon Running

Oxidative phosphorylation is a process by which carbohydrates, fats, or proteins can be metabolized through a series of chemical reactions to release the energy necessary to phosphorylate ADP to ATP

Oxidative phosphorylation, known as the aerobic energy system, can be used to supply ATP on a continuous basis, as long as oxygen and sources of fuel are available.

Why is it undesirable to use protein as a fuel source?

Protein is not "stored" as an energy source in the same sense as are carbohydrates (as glycogen) and fats (as triglycerides, predominantly in adipose tissue). Proteins are typically incorporated into functional (for example, enzymes) or structural (for example, skeletal muscle) elements in the body. - Along with the additional steps required to remove and dispose of the nitrogen groups, these limitations prevent protein from making up a large portion of the fuel sources for metabolism, particularly during exercise. -Under metabolically stressful conditions, such as starvation or exercise in a glycogen-depleted state (for example, latter stages of a marathon), protein may compose a larger percentage of the fuel utilization, but it rarely exceeds 10 percent of total energy production.

What must happen for an amino acid to be metabolized aerobically?

Proteins are broken down into amino acids ---> Amino acids can be metabolized aerobically after the amino- or nitrogen-containing group has been removed --> Nitrogen groups are typically removed by either being transferred to another compound (transamination) or being removed completely (deamination)

What is a rate limiting enzyme? What the is name of one in glycolysis?

Rate limiting enzyme- In a series of chemical reactions, the enzyme that influences the rate of the entire series of reactions by changes in its activity - ex: there is an enzyme that controls the speed of all the reactions in the same way that the overall speed of an assembly line is governed by the speed of the slowest worker Glycolysis - The rate-limiting enzyme for glycolysis is phosphofructokinase (PFK), which catalyzes the third step. If the activity of PFK increases, the entire reaction speeds up, and if PFK activity decreases, the entire reaction slows down.

Describe the Krebs cycle

The Krebs cycle is a series of 10 chemical reactions that begin with acetyl CoA (a two-carbon compound) joining with oxaloacetate (four carbons) to form a six-carbon compound, citric acid - One of the Krebs cycle reactions is exergonic and releases enough energy to produce a high-energy phosphate compound, guanosine triphosphate (GTP), which is then used to form an ATP. In four of the oxidation-reduction reactions, NAD is the electron acceptor, and in one, FAD is the electron acceptor. - The vitamins niacin (that is, nicotinic acid and nicotinamide) and riboflavin are major components of NAD and FAD, respectively. NAD and FAD shuttle the electrons to the final major component of oxidative phosphorylation, the electron transport chain. *With the two turns of the Krebs cycle, 6 NADH are formed, giving a total of 8 NADH when combined with the 2 formed in the conversion of pyruvate to acetate

What increases the activity of PFK (phosphofructokinase) in glycolysis?

The activity of PFK is dramatically increased, however, by a drop in the concentration of ATP and the concomitant rise in ADP concentration—this is an important signal that ATP is being used up and must be replenished.

How does glycolysis differ from creatine phosphate system in the amounts used and found in the body?

The body has a considerable amount of carbohydrate energy in the form of blood glucose and muscle glycogen, so unlike the creatine phosphate system, the anaerobic glycolytic energy system is rarely limited by depleted energy stores.

What amino acids can be relatively easily metabolized by skeletal muscle?

The branched chain amino acids, leucine, isoleucine, and valine, can be relatively easily metabolized by skeletal muscle.

What energy system is the preferred energy system for high intensity exercise?

The creatine phosphate system; because of the speed with which the CrP can act to replenish ATP, it is the preferred energy system during very high-intensity exercise, during which ATP is utilized very rapidly.

How long is the duration of this energy system?

The duration of this energy system is said to be 1 to 2 minutes. - It begins to function at the onset of high-intensity exercise but becomes the predominant energy system after 5 to 10 seconds when the creatine phosphate energy system begins to reach its limit. **Anaerobic glycolysis utilizes only carbohydrate as a fuel source, and it can replace ATP rapidly during moderately high to high-intensity exercise.

Creatine Phososphate

The most prevalent high-energy phosphate in the body is ATP, but there is another high-energy phosphate compound that is stored in muscle and other tissues—creatine phosphate (CrP, CP or PCr, PC aka phosphocreatine). - Potential energy is stored in the phosphate bond of creatine phosphate --> energy released from the breakdown of creatine phosphate is used to phosphorylate ADP into ATP - Creatine phosphate stored in muscle acts as a readily accessible reservoir of energy for the re-formation of ATP.

Oxidation vs Reduction

The process of giving up electrons is called oxidation, and the compound that has electrons removed has been oxidized. The process of accepting electrons is called reduction, and the compounds that receive the electrons have been reduced.

The Respiratory Exchange Ratio (RER) or Respiratory quotient Indicates Utilization of Carbohydrate and Fat as Fuels

The proportion of energy coming from carbohydrates and fats can be estimated accurately by use of the respiratory exchange ratio (RER), ratio of the amount of carbon dioxide produced to the amount of oxygen consumed RER= Vco2/ Vo2 vco2- carbon dioxide production vo2- oxygen consumption *In the example of palmitate, 23 oxygen molecules are needed for complete oxidation, resulting in the production of 16 carbon dioxide molecules. The resulting (16 produced divided by 23 consumed), indicating that fat is the only source of fuel.

What is the rate limiting enzyme for the electron transport chain?

The rate-limiting enzyme for the electron transport chain is cytochrome oxidase (COX).

What is the rate limiting enzyme for the Krebs cycle?

The rate-limiting enzyme for this series of reactions is isocitrate dehydrogenase (IDH)

What compounds get reduced during respiration?

The two most common electron-accepting compounds are nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD).

How much ATP is produced during aerobic respiration?

Therefore, the net ATP for aerobic metabolism of glucose in skeletal muscle is 30 ATP. In other tissues, the net ATP may be 32. - If the starting point is glycogen rather than glucose, 1 ATP is saved, bringing the total ATP produced to 31 or 33, depending on the type of tissue.

The utilization of carbohydrate, fat, and protein as fuel is complex and depends on a variety of factors

diet composition, activity level, health and/or disease state, hormonal status, and time since the last meal.

In the fed state, the most important hormone is

insulin, and the body's energy priority is delivering glucose from carbohydrate-containing foods - Insulin affects cell membranes so glucose can be taken up by the cells and used immediately for energy. It also favors the storage of glycogen by activating the enzymes that help cells store glycogen and inhibiting the enzymes that break down glycogen. - has an enormous effect on fat storage and creates an environment in which fat from food can be readily stored as body fat. *When nonobese people are in energy balance, carbohydrate is primarily used for immediate energy or glycogen storage. Essentially none is converted to fatty acids and stored as fat.

Why is muscle fatigue considered a protective mechanism?

it is potentially disastrous to a muscle cell to have ATP concentrations drop to very low levels, so the muscle uses fatigue as a protective mechanism to prevent ATP depletion. - Very low levels of CrP in the muscle are also associated with muscle fatigue - When a muscle begins to fatigue, it fails to produce force at the same level or the same rate. Because it is not producing force at the same rate, the requirement for ATP declines, and it is not used up as rapidly.