Energy Metabolism

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energy metabolism

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an elaborate multiset series of energy-transforming chemical reactions

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Metabolism

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The entire network of chemical processes involved in maintaining life. It covers all the sequences of chemical reactions that occur in the body. Theses reactions enable us to release and use energy from carbs, fats, protein, and alcohol. They allow use to synthesize one substance from another and prepare waste products for excretion

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Metabolic pathway

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a group of biochemical reactions that occur in a progression from beginning to end

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Intermediates

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Compounds formed in one of the many steps in a metabolic pathway

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Catabolic Pathways

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these breakdown compounds into small units. The glycogen molecule is broken down into many glucose molecules.

Energy is released during catabolism: some is trapped for cell use and the rest is lost to heat

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Anabolic Pathways

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they use small, simpler compounds to build larger more complex compounds

This process takes energy

ex: Glycogen formation

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Anabolic and Catabolic Pathways

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the body strives for balance between these two processes. There are times however when some process are more important than others.

Ex: growth - anabolic increases

weight loss - catabolic increases

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Energy for the cell

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Cells use energy to build compounds, contract muscles, conduct nerve impulses, or pump ions

Energy comes from catabolic reactions which break the chemical bonds between the atoms in carbs, fat, protein, and alcohol.

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Adenosine Triphosphate (ATP)

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the main form of energy the body uses

only the energy in ATP and related compounds can be used directly by the cell.

ATP consists of adenosine (adenine and sugar ribose) bound to 3 phosphate groups.

ATP can be rebuilt and broken down throughout the body

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Adenosine diphosphate (ADP)

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the release of energy in ATP, cells break the a high-energy phosphate bond, which creates adenosine diphosphate

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Adenosine Monophosphate (AMP)

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Hydrolysis of ADP results in AMP in a reaction muscles are capable of performing during intense exercise when ATP is in short supply

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Oxidation-Reduction reactions in Energy Metabolism

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Synthesis of ATP from ADP and Pi involves the transfer of energy from energy-yielding compounds (proteins, carbohydrate, fat, and alcohol). Electrons (hydrogen ions) are transferred to oxygen. These reactions release a lot of energy which can be used to produce ATP.

Enzymes control oxidation-reduction reactions in the body.

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Dehydrogenases

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One type of enzyme

Removes hydrogens from energy-yielding compounds or their breakdown products.

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Coenzyme

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compound that combines with an inactive protein called apoenzyme to form a catalytically active protein, called a holoenzyme. In this manner coenymes aid in enzyme function.

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Nicotinamide adenine dinulceotide (NAD)

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Found in cells as both its oxidized form (NAD) or its reduced form (NADH).

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Cellular respiration

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Oxidizes (removes e-) food molecules to obtain energy (ATP). Oxygen is the final electron acceptor. When oxygen is readily available it is aerobic when oxygen is not present it is anerobic

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Aerobic

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Requiring oxygen

Much more efficient than anaerobic respiration

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Anaerobic

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Not requiring oxygen

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Stages of aerobic cellular respiration

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1. Glycolysis

2. Transition reaction

3. Citric acid cycle

4. Electron transport chain

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Glycolysis

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In this pathway glucose is oxidized and forms 2 molecule sof the 3 carbon compound pyruvate, produces NADH + H+, and generates a net of 2 molecules of ATP.

Occurs in the cytosol of the cell

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Cytosol

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Water based phase of a cell's cytoplasm, excludes organelles, such as mitochondria.

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Transition Reaction

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In this stage, pyruvate is further oxidized and joine with coenzyme A (CoA) to form acetyle-CoA. The transition reaction also produces NADH + H+, and releases CO2 as waste.

Takes place in the mitochondria of cells

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Mitochondria

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Main sites of energy production in a cell. They also contain the pathway for oxidizing fat for fuel, among other metabolic pathways.

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Citric acid cycle

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In this pathway, acetyl-CoA enters the citric acid cycle, resulting in the production of NADH + H+, FADH2, and ATP. Carbon dioxide is released as waste

Take place in the mitochondria

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Glycolysis

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"breakdown of glucose"

breaks down carbs to generate energy to provide building blocks for synthesizing other needed substances

convert into pyruvate

only requires B-vitamin niacinas NAD

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Transition Reaction: synthesis of Acetyl CoA

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Pyruvate passes from cytosol into the mitochondria, where the pyruvate dehydrogenase enzyme complex converts pyruvate into the compound acetyl-CoA in the process called a transition rxn.

Irreversible. Requires 4 B-vitamins - thiamin, riboflavin, niacin, and pantotheic acid.

each glucose yields 2 acetyl- CoA. The 2 NADH + H+ will enter the electron transport chain

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Citric Acid Cycle

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The acetyl-CoA molecules produced by the transition rxn enters the citric acid cycle. Converts the carbons of an acetyl group to carbon dioxide while harvesting energy to produce ATP.

Takes 2 turns around the citric acid to process 1 glucose molecule because glycolysis and the transition rxn yield 2 acetyl-CoA. Each tun around produces 2 CO2, and 1 ATP ( in the form of GTP), an 3 molecules of NADH + H+, and 1 molecule of FADH2.

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Electron Transport Chain

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The final pathway of aerobic respiration is the electron transport chain located in the mitochondria.

Involves the passage of electrons along a series of electron carriers. As e- are passed energy is released.

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Oxidative Phosphorylation

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metabolic process

way in which energy is derived from the NADH + H+, and FADH 2 is transferred to ADP + Pi to form ATP.

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Importance of Oxygen

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NADH + H+ & FADH2 produced during the citric acid cycle can be regenerated into NAD+ and FAD only by the eventual transfer of their electrons and hydrogen ions to oxygen, as occurs in the electron transport chain.

Oxygen is the final acceptor of the electrons and hydrogen ions generated from the breakdown of energy-yielding nutrients. Without oxygen most of our cells are unable to extract enough energy from energy-yielding nutrients to sustain life.

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Anaerobic Metabolism

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Some cells lack mitochondria and are unable to do aerobic respiration. Other cells are capable of turning to anaerobic metabolism when oxygen is lacking.

When oxygen is absent, pyruvate that is produced through glycolysis is converted into lactate or lactic acid.

It is not as efficient because it only converts about 5% of glucose into ATP.

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Synthesis of Lactate

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Pyruvate + NADH + H+ --> Lactate + NAD+

Catalyzed by the enzyme pyruvate dehydrogenase

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ATP production from fats

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Cells can releases and trap energy in triglyceride molecules.

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Lipolysis

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the breakdown of triglycerides into free fatty acids and glycerol.

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Fatty acid oxidation

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breakdown of fatty acids for energy production

electrons are donated from fatty acids to oxygen to yield ATP

Happens in mitochondria

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Carnitine

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helps shuttle free fatty acids in the cytosol into mitochondria

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Process of creating ATP from Fatty Acids

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1. cleave carbons 2 at a time and convert into acetyl-CoA (beta-oxidation). NADH + H+ and FADH2 are produced. Fatty acid is degraded into a number of 2 carbon compound acetyl-CoA

2. The acetyl-CoA enters the citric acid cycle. 2 CO2 are released and acetyl-CoA is produced. Each fatty acid results in the production of 7 ATP>

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Carbohydrate Aids Fat Metabolism

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the citric acid cycle provides compounds that leave the cycle to enter biosynthetic pathways.

This slows the cycle as eventually not enough oxaloacetate is formed to combine with the acetyl-CoA entering the cell. Cells are able to compensate by synthesizing additional oxaloacetate. This is done by using pyruvate (from glucose)

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Ketone bodies

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incomplete breakdown products of fat, containing 3 or 4 carbons. Most contain a chemical group called a ketone. An example is acetoacetic acid.

they are the product of incomplete fatty acid oxidation.

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Ketosis

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condition of having high concentrations of ketone bodies and related breakdown products in the bloodstream and tissues.

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Ketosis in Diabetes

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in type 1 diabetes, little to no insulin is produced. This lack does not allow for normal carbohydrate and fat metabolism. Cells cannot utilize glucose whcih leads to excess production of ketone bodies.

Diabetic Ketoacidosis- leads to coma or death

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Ketosis in semistarvation or Fasting

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when a person starves the amount of glucose falls. The fall in blood insuling causes fatty acids to flood into the bloodstream and eventually form ketone bodies in the liver. The heart, muscles, and some parts of the kidney then use ketone bodies for fuel. This adaptive response is important to semistarvation or fasting. As more body cells begin to use ketone bodies for fuel the need for glucose diminishes. Allowing the maintenance of protein mass is key to survival.

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Protein Metabolism

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takes place in the liver. amino acids that are branched are metabolized mostly at other sites (muscles).

Protein metabolism begins after proteins are degraded into amino acids. To use these as fuel cells must first deaminate them (remove the amino group). These require vitamin B-6 to function. Remove of the amino group produces carbon skeletons which enter the citric cycle. Some carbon skeletons also yield acetyl-CoA or pyruvate.

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Glucogenic amino aids

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these carbons can become the carbons of glucose

ex: isoleucine, methionine, proline etc.

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ketogenic amino acids

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these carbons cannot become parts of glucose molecules

ex: leucine and lysine

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Gluconeogensis

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Generation of new glucose from certain amino acids

occurs in the liver and certain kidney cells.

1. mitochondria produces oxaloacetate.

2. Returns to cytosol where it loses 1 CO2, forming phosphoenolpyruvate

3. Reverses path back through glycolysis to glucose.

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Why is gluconeogensis from typical fatty acids not possible

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because those with an even number of carbons break down into acetyl-CoA molecules. They never re-form into pyruvate. the step between pyruvate and acetyl-CoA is irreversible.

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Disposal of Exess Amino Groups from Amino Acid Metabolism

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Catabolism of amino acids makes ammonia this must be excreted because it is toxic to the cells. The liver prepares the amino groups for excretion int he urine with the urea cycle.

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Alcohol Metabolism

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the alcohol dehydrogenase (ADH) pathway is the main pathway for alcohol metabolism. Alcohol is converted in the cytosol to acetaldehyde by the action of the enzyme alcohol dehydrogenase and the coenzyme NAD+

NAD+ picks up 2 hydrogen ions and 2 electrons to form NADH+ H+ and produces the intermediate acetaldehyde. This is then converted to acetyl COA yielding NADH+H+

Occurs in the liver

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Regulating the Energy Metabolism

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1. Liver- many nutrient interconversions

2. ATP concentrations

3. Enzyme, Hormones, Vitamins, and Minerals- presence and their rate of activity are critical to chemical reactions in the body

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Fasting

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During the first few hours the body with fuel itself with stored liver glycogen and fatty acids from adipose tissue. The body at continues to be broken down and liver glycogen becomes exhausted. The nervous system and the red blood cells use only glucose for energy. The body breaks down lean body tissue and converts to glucose. Blood urea levels increase because of the breakdown of protein.

death would occur in 7-10 weeks

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Feasting

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increase insulin production by the pancreas which encourages the burning of glucose for energy as well as the synthesis of glycogen an protein and fat.

Fat consumed in excess immediately goes into storage as adipose cells.