Muscular System: Muscle Metabolism Essay

Muscular System: Muscle Metabolism 1. List the three roles of ATP in muscle contraction: 1. _Energize the power stroke of the myosin cross bridge. 2. _Disconnecting the myosin head from the binding site on actin at the conclusion of a power stroke. 3. _Energizing the calcium ion pump. 2. The potential energy in ATP is released when the terminal high-energy bond is broken by a process called hydrolysis. Write the end products of this process: ATP (+ H2O) ( ADP 3. Rebuilding ADP into ATP with a new source of energy is carried out by a process called dehydration synthesis. Muscular System: Muscle Metabolism Essay.

Write the equation for this process: ADP ( ATP (+ H2O) 4. List the three processes used to synthesize additional ATP when ATP supplies are low: 1. Hydrolysis of creatine phosphate 2. Glycolysis 3. The Krebs cycle and oxidative phosphorylation 5. An immediate source of energy is creatine phosphate (CP), but the supplies are limited and rapidly depleted. One molecule of CP produces one ATP. 6. Glucose is a major source of energy for synthesizing ATP. List the two sources of glucose: 1. Glucose enters the muscle cell directly from the blood. . Glucose is produced by hydrolysis of glycogen stored in the muscle cell. 7. Glycolysis is the process that breaks down glucose. Name two products of the breakdown of glucose: 1. Two ATP molecules 2. Pyruvic acid If oxygen is not available, pyruvic acid is converted to lactic acid, which is the end product of anaerobic respiration. 8. If oxygen is available, the process is known as ___aerobic_ respiration. Name two sources of oxygen: 1. Oxygen enters the muscle cell directly from the blood. 2. Oxygen is stored in myoglobin, an oxygen-binding protein.

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The aerobic pathway consists of glycolysis + krebs cycle + oxidative phosphorylation. The net result of one glucose molecule is 36 ATP. 9. The process of restoring depleted energy reserves after exercise is called repaying the oxygen debt. Name four processes that occur during this time: 1. Lactic acid is converted back to pyruvic acid, which enters the Krebs cycle, producing ATP. 2. This ATP is used to rephosphorylate creatine into creatine phosphate. 3. Glycogen is synthesized from glucose molecules. 4. Muscular System: Muscle Metabolism Essay. Additional oxygen re-builds to myoglobin. 0. Put the following characteristics under the correct fiber type in the table below: Krebs cycle and oxidative phosphorylationuses glycolysis fatigue rapidlyhigh endurance few capillariesmany capillaries much myoglobinlittle myoglobin long-distance runnersprinter Krebs cycle and oxidative phosphorylation uses glycolysis fatigue rapidly high endurance few capillaries many capillaries much myoglobin little myoglobin long-distance runner sprinter light in color, large diameter red in color, small diameter Red Slow-Twitch Fibers |White Fast-Twitch Fibers | |Krebs cycle and oxidative phosphorylation |Uses glycolysis | |Many capillaries |Little myoglobin | |Red in color, small diameter |Few capillaries | |High endurance |Light in color, large diameter | |Long-distance runner |Fatigue rapidly | |Much myoglobin |Sprinter |

Did you know our muscles use billions of molecules every second to contract? This lesson describes the different metabolic processes by which ATP is generated by the muscle cell. Examples are utilized to define glycolysis, the citric acid cycle and oxidative phosphorylation.

ATP is the Energy Source

Believe it or not, I rode my bike from St. Louis, MO, to Chicago, IL, when I was in college. One of my favorite parts of that trip (as well as training for the trip) was eating as much as I wanted. I ate as much of whatever I felt like eating, and I was still fit as a fiddle. Our muscles comprise a large amount of our body mass, and they require enormous amounts of energy to contract. As my muscles were contracting a lot while riding my bike, they needed a lot of energy. Even at rest, our muscles require a lot of energy. Where does the energy come from? Muscular System: Muscle Metabolism Essay.

ATP (adenosine triphosphate) provides the energy for muscular contraction.

Ultimately, energy comes from the food we eat. Muscle cells, however, don’t use sugar, fats or proteins to contract. Rather, our cells convert the energy stored in those nutrient molecules into energy stored within ATP(adenosine triphosphate). That’s the universal energy molecule for living cells. ATP, in turn, provides the energy needed for muscular contraction. Exercising muscle gobbles up billions of ATP molecules every second. In this lesson, we’ll describe how our muscle cells utilize energy from nutrients to make ATP and, therefore, contract.

ATP and Creatine Phosphate

While resting, skeletal muscle makes more ATP than it needs. As ATP is not very stable, the excess ATP transfers energy to creatine. That’s a molecule made by our muscles from amino acids. This is the reaction: ATP + Creatine -> ADP + Creatine Phosphate (CP).

So, you see, the phosphate is transferred from ATP to creatine to make creatine phosphate. As creatine phosphate, or phosphocreatine, is more stable than ATP, it provides an effective way to store energy. During contraction, the contractile protein myosin breaks down ATP producing ADP and phosphate. The energy stored in creatine phosphate is then used to recharge the ADP as follows: CP + ADP -> Creatine + ATP.

So, you see, the phosphate is now transferred back to ADP to make ATP, and the ATP can be used for contraction. These reactions are catalyzed by the enzyme we call creatine phosphokinase (or CPK), and it’s located in the muscle cell. CPK leaks into the bloodstream when muscles are damaged. For example, this happens with a myocardial infarction, or a heart attack, that results in heart muscle damage. Clinical tests are used to measure circulating levels of CPK and thus, assess the level of muscle damage. Muscular System: Muscle Metabolism Essay.

It is important to note that ATP and CP reserves are exhausted within about 15 seconds of exercise. That’s not very long. Therefore, the cell must be able to generate, or synthesize, ATP if it is to continue working.

Glycolysis

The process of breaking down sugar used to make ATP is called glycolysis.

The beginning of ATP synthesis in the cell is termed glycolysis. During glycolysis, energy is released from the breakdown of sugar, and it’s used to make ATP. Specifically, glucose is broken down to pyruvic acid (or pyruvate) in the cell’s cytoplasm. Glycolysis is an anaerobicprocess, as it does not require molecular oxygen. Let me quickly note that glycolysis can occur in the presence of oxygen, it simply doesn’t need it.

In the absence of molecular oxygen, however, glycolysis is the only source of ATP. During glycolysis, each glucose molecule is broken down into two pyruvic acid molecules. This is a multi-step process, and it produces four ATP molecules. However, two ATP molecules are used early in the process of glycolysis, and that yields a net gain of only two ATP per glucose going through glycolysis. That’s not very much. Let me quickly note that pyruvic acid is converted into lactic acid in the absence of oxygen. Lactic acid, at least in part, is responsible for muscle cramping.

Because only two ATP molecules are gained for each glucose molecule, we need a lot of glucose to support anaerobic metabolism. Glycogen is a large molecule made up of a whole bunch of individual glucose molecules, and it provides a store of glucose for the muscle cells. Eventually, however, our glycogen stores run out and aerobic synthesis of ATP is needed, which we’ll talk about next. Muscular System: Muscle Metabolism Essay.

In order for muscles to contract, ATP must be available in the muscle fiber. ATP is available from the following sources:

• Within the muscle fiber. ATP available within the muscle fiber can maintain muscle contraction for several seconds.
• Creatine phosphate. Creatine phosphate, a high‐energy molecule stored in muscle cells, transfers its high‐energy phosphate group to ADP to form ATP. The creatine phosphate in muscle cells is able to generate enough ATP to maintain muscle contraction for about 15 seconds.
• Glucose stored within the cell. Glucose within the cell is stored in the carbohydrate glycogen. Through the metabolic process of glycogenolysis, glycogen is broken down to release glucose. ATP is then generated from glucose by cellular respiration.
• Glucose and fatty acids obtained from the bloodstream. When energy requirements are high, glucose from glycogen stored in the liver and fatty acids from fat stored in adipose cells and the liver are released into the bloodstream. Glucose and fatty acids are then absorbed from the bloodstream by muscle cells. ATP is then generated from these energy‐rich molecules by cellular respiration.

Cellular respiration is the process by which ATP is obtained from energy‐rich molecules. Several major metabolic pathways are involved, some of which require the presence of oxygen. Here’s a summary of the important pathways:

• In glycolysis, glucose is broken down to pyruvic acid, and two ATP molecules are generated even though oxygen is not present. The production of ATP without the use of oxygen is called anaerobic respiration, and, because no oxygen is used during the various metabolic steps of this pathway, glycolysis is called an anaerobic process. Muscular System: Muscle Metabolism Essay.
• During anaerobic respiration, pyruvic acid is converted to lactic acid. Lactic acid (via liver enzymes) can be converted back to pyru‐vic acid and, with the presence of oxygen, pyruvic acid can enter the mitochondria.
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Anaerobic respiration has advantages and disadvantages:

• Advantages: Anaerobic respiration is relatively rapid, and it does not require oxygen.
• Disadvantages: Anaerobic respiration generates only two ATPs and produces lactic acid. Most lactic acid diffuses out of the cell and into the bloodstream and is subsequently absorbed by the liver. Some of the lactic acid remains in the muscle fibers, where it contributes to muscle fatigue. During strenuous exercise, a lot of ATP needs to be produced. Since a person is exercising faster than they are bringing in oxygen, the body tries to make ATP using the anaerobic pathway. This results in the production of ATP and lots of lactic acid. After exercise, the liver and muscles need to convert the lactic acid back to pyruvic acid. In order to do that, a lot of the oxygen the body is now taking in does the conversion instead of being used elsewhere. This is known as “repaying the debt,” hence the term “oxygen debt.”
• In aerobic respiration, pyruvic acid (from glycolysis) and fatty acids (from the bloodstream) are broken down, producing H ₂O and CO ₂ (carbon dioxide) and regenerating the coenzymes for glycolysis. A total of 36 ATP molecules are produced (including the two from glycolysis). However, oxygen is required for this pathway.

Aerobic respiration also has advantages and disadvantages:

• Advantages: Aerobic respiration generates a large amount of ATP.
• Disadvantages: Aerobic respiration is relatively slow and requires oxygen. Muscular System: Muscle Metabolism Essay.

When the ATP generated from creatine phosphate is depleted, the immediate requirements of contracting muscle fibers force anaerobic respiration to begin. Anaerobic respiration can supply ATP for about 30 seconds. If muscle contraction continues, aerobic respiration, the slower ATP‐producing pathway, begins and produces large amounts of ATP as long as oxygen is available. Eventually, oxygen is depleted, and aerobic respiration stops. However, ATP production by anaerobic respiration may still support some further muscle contraction. Ultimately, the accumulation of lactic acid from anaerobic respiration and the depletion of resources (ATP, oxygen, and glycogen) lead to muscle fatigue, and muscle contraction stops. Muscular System: Muscle Metabolism Essay.