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Physiology Exam 1 (Part 2) Energy Metabolism
Terms in this set (28)
78. State the First Law of Thermodynamics.
"In all energy transformations, energy is neither created nor destroyed, it only changes form."
79. State the Second Law of Thermodynamics.
"In all spontaneous energy transformations, the energy of the final state will be less than the energy of the initial state"
80. In biochemistry, what is a 'downhill' reaction? An 'uphill' reaction? Which type of reaction will occur spontaneously and releases energy? Which type of reaction does NOT occur spontaneously and will require energy to be put added to the reactant side of the equation in order for the reaction to occur? Explain 'spontaneous' chemical reactions and 'non-spontaneous' chemical reactions in terms of the second law of thermodynamics.
Downhill reaction: A spontaneous reaction where the products will have less energy than the reactants due to energy being lost to the environment.
Uphill reactions: A reaction that where the products will have more energy than the reactants. This doesn't occur naturally (non-spontaneous), so the body turns uphill reactions into downhill reactions by putting in energy in the form of ATP.
81. Is the hydrolysis (breakdown) of ATP an uphill (non-spontaneous) or downhill(spontaneous) reaction? Does the hydrolysis of ATP require energy or does it release energy? Is the dehydration synthesis of ATP an uphill or downhill reaction? Does the dehydration synthesis of ATP require energy or release energy?
Hydrolysis (breakdown using water) of ATP is a downhill reaction (non-spontaneous). The breakdown of ATP to ADP releases 7.30 kcal/mol of energy. Dehydration synthesis of ATP is an uphill reaction because it requires energy to attach Pi to ADP.
82. The breakdown of ATP provides energy for the uphill (energy requiring) biochemical reactions of life. By adding enough ATP to the reactant side of an equation, the cell is able to turn an uphill reaction into a downhill reaction. Thus, energy demanding reactions can be made possible. The only limitation to this concept is that the uphill reactions must occur as a series of small steps. A steep downhill reaction is, itself, irreversible.
83. Where does the energy come from to make ATP? Draw the structure of ATP and identify the adenine nucleotide, the ribose sugar, and the three phosphate bonds. Is ATP used for uphill or downhill reactions in the cell? Is ATP needed for ALL chemical reactions in the body? See the glycolysis reaction pathway.
ATP (adenosine triphosphate) is made up of a ribose sugar, an adenine base, and three phosphate groups. ATP is needed to provide the energy for uphill reactions, but not needed for all chemical reactions in the body (a lot of downhill reactions actually produce ATP).
84. In a single sentence, what is Aerobic Cellular Respiration? Write the overall chemical equation, reactants to products, for aerobic cellular respiration? In a single sentence, what is Anaerobic Cellular Respiration? Write the overall equation for anaerobic cellular respiration. What is the total useful energetic yield (ie. how much ATP) from each of these two respiration reaction pathways?
Aerobic Cellular Respiration: The process by which the body generates ATP.
C6H12O6 + 6 O2 ===> 6 CO2 + 6 H2O + 38 ATP
Anaerobic Cellular Respiration: The process by which the body generates ATP in the absence of oxygen.
C6H12O6 ===> 2 lactic acid + 2 ATP
85. What major chemical events occur during each of the four stages of aerobic cellular respiration: Glycolysis, Transitional Step, Kreb's Cycle, and Electron Transport Chain? For each stage, determine the following: What basically happens in each stage? What is produced that is useful? What is produced that is waste? What chemicals are recycled? How many different enzymes are required for glycolysis, transitional step, Kreb's cycle, ETC?
Where, specifically, does each stage occur in the cell? What might be the chemical consequences for the cell if any one of the many enzymes in these four reaction pathways was produced by mutated genes and and thereby structurally altered?
Glucose (6C's) ===> 2 pyruvates (3C's) + 2 NADH + 2 ATP
2) Transitional Step:
2 pyruvates (3C's) ===> 2 acetyl-CoA's (2C's) + 2 NADH
3) Kreb's Cycle (net change after reaction happens twice):
2 acetyl-CoA's (2C's) ===> 6 NADH + 2 FADH2 + 2 ATP
4) Electron Transport Chain:
NADH = 3 ATP
FADH2 = 2 ATP
10 NADH + 2 FADH2 = 10(3) + 2(2) = 34 ATP
Total energy: 38 ATP
Glycolysis occurs in the cytoplasm of the cell, the transitional step and Kreb's cycle take place in the mitochondrial matrix, and ETC take place inside the mitochondrial membrane.
86. Why are some biochemical reactions 'reversible' while others are 'irreversible'? Hint: the more energy released by a reaction, the more irreversible it is. Why? If a reaction is reversible, the Law of Mass Action can apply. What is the Law of Mass Action? This will be important to understanding gluconeogenesis.
If you release energy all at once instead of in small steps, you would get a combustion.
Law of Mass Action: In a reversible reaction, an equilibrium between the reactants and products will occur when the concentrations of the reactants and products stabilize and cease to change.
87. Coenzymes and trace metals are known as Cofactors. Many, but not all, enzymes cannot work without cofactors. Don't be confused by the terms Coenzymes and Cofactors. A Coenzyme is one type of Cofactor. Many vitamins are necessary to make Coenzymes. Vitamins cannot be produced by the body and thus must be acquired in the diet. Trace metals are the other type of Cofactor. Calcium, Magnesium, Sodium, Iron, Zinc and many other trace metals must also be consumed in the food we eat. Cofactors, ie vitamins and trace metals, are necessary for normal cell functioning.. Because they are recycled, they are only needed in small amounts.
Coenzymes are necessary for energy metabolism: The coenzymes NAD+, Nicotinamide Adenine Dinucleotide, and FAD+, Flavin Adenine Dinucleotide, are critical to cell respiration and fatty acid metabolism. However, the body cannot make NAD+ without Vitamin B3 (Niacin) in the diet. Similarly, the body cannot make FAD+, without Vitamin B2 (Riboflavin) in the diet. NAD comes in two forms, charged (NAD+) and uncharged, bonded to hydrogen (NADH). Same with FAD, (FAD+ and FADH2). Where and how in the various biochemical reaction pathways does NAD+ become NADH? Give three examples. Where and how in the various biochemical reaction pathways does FAD+ become FADH2? These conversions of NAD+ and FAD+ coenzymes from charged states to NADH and FADH2 are easily reversible. This fact enables vitamins and coenzymes to be easily recycled in the body. Thus, we only need vitamins in small amounts. This raises the question about the usefulness of taking mega-doses of vitamins. Excess doses of water soluble vitamins like the B vitamins, niacin and riboflavin, and vitamin C only come out in the urine as the body excretes the amounts of vitamins it doesn't use. Vitamin B-12 is the exception. It is stored in the liver.
In Glycolysis, NAD+ is converted into NADH twice when the dihydroxyacetone phosphates (broken fragments of fructose ring) are converted into 1,3 bisphosphoglycerate
In the Transitional Step, NAD+ (coenzyme made by Vitamin B3) is made into NADH twice when pyruvic acid (3C's) is converted into acetyl coenzyme A (2C's)
In the Kreb's cycle, 6 NAD+'s are made into 6 NADH's through 2 cycles at 3 instances:
1) isocitric acid (C6) ===> α-Ketoglutaric acid (C5)
2) α-Ketoglutaric acid (C5) ===> Succinic acid (C4)
3) Malic acid (C4) ===> Oxaloacetic acid (C4)
88. Which of the four stages of aerobic cellular respiration will cease to occur in the absence of vitamins B2 and B3?
Vitamins B2 and B3 are used to generate riboflavin for FADH2 and nicotinic acid for NADH respectively. Without NADH or FADH2, ETC would not be able to pump electrons through the ion channels to produce ATP.
89. Coenzyme A is another coenzyme critical to cell respiration. Like the coenzymes, niacin and riboflavin, the body cannot make Coenzyme A without a vitamin in the diet. That vitamin is Vitamin B5 (Pantothenic acid). Check your cereal boxes, you will find vitamins Niacin B2, Riboflavin B3, and Pantothenic acid B5 all listed by name. Note all these B vitamins are involved in energy metabolism, ie. the production of ATP.
90. What are the specific functions of each of the following coenzymes: NAD+, FAD+, and Coenzyme A? What specific chemical role does each perform?
NAD+: Used to carry high energy electrons to the ETC.
FAD+: Used to carry high energy electrons to the ETC.
Coenzyme-A: Used in the Kreb's cycle to produce 3 NADH, 1 FADH2, and 1 ATP
92. Given that each NADH yields 3 ATP at the ETC, and each FADH2 yields 2 ATP, what is the total number of ATP generated from 1 molecule of glucose?
91. What is the energy yield of:
1) glycolysis (2 ATP's)
2) transitional step (0 ATP)
3) Kreb's cycle (2 ATP's)
4) electron transport chain (34 ATP's)
How is the hydrogen ion gradient created between in the inner membrane space and the matrix of the mitochondrion? Specifically, what chemical work is accomplished as electrons move down the electron transport chain? If the hydrogen ion gradient was lost, that is, if the concentrations of hydrogen ions on either side of the inner mitochondrial membrane became equivalent, what could not happen? Where do the electrons traveling down the electron transport chain ultimately end up? At what specific structure is ATP produced, and how does ATP synthesis occur?
NADH and FADH2 pass high energy electrons to power intermembrane protein complexes to pump H+ ions out of the membrane. The higher concentration of H+ ions on the outside creates a gradient through ATP synthase so ADP is attached to a Pi when they're pumped back in. When electrons are done going down the ETC, they're picked up by oxygen to form water. FADH2 joins the ETC later which is why it yields less energy than NADH.
93. How does anaerobic respiration differ from aerobic respiration? What is the energy yield of anaerobic respiration from one molecule of glucose? How does this compare to the energy yield of aerobic respiration?
Anaerobic respiration converts glucose into 2 ATP and 2 lactic acid. This conversion also regenerates NAD+ from NADH to make the transition from fructose fragments into pyruvate into lactic acid repeatable. Lactic acid can then be converted back into pyruvic acid back into fructose 6-phosphate back into glucose.
94. What is the end product of anaerobic respiration pathway? What are the end products of aerobic respiration pathways? In anaerobic respiration, what eventually happens to lactic acid in the liver? See Cori Cycle. Why do we pant after running ? Answer: we need the molecular oxygen from increased ventilation of the lungs to produce the ATP needed to convert the lower energy lactic acid back to the higher energy compounds of glucose and glycogen. This is the Cori Cycle. It occurs in the liver.
The end product of anaerobic respiration pathway is 2 ATP and 2 lactic acid. In the liver, lactic acid is converted back into glucose using ATP through the Cori Cycle. After we run, we pant to regain oxygen to convert the lactic acid produced by anaerobic respiration back into glucose.
95. What is gluconeogenesis? Why is gluconeogenesis so important to the body? In what organ does gluconeogenesis occur? Amino acids and lactic acid can be converted into pyruvate. Pyruvate can be converted into oxaloacetate. Oxaloacetate can be converted into glucose. Why such a circuitous route? Why can't pyruvate be converted directly back into glucose simply by going back up the glycolytic pathway by way of phosphoenolpyruvate?
Gluconeogenesis: Production of glucose from non-carbohydrate sources (lactic acid, amino acids, glycerol).
This occurs in the liver, kidney, and small intestine.
Oxaloacetate can be converted into phosphoenolpyruvate which can be converted back into glucose via a series of reversible reactions. The conversion from phosphoenolpyruvate to pyruvate is an irreversible downhill reaction due to the large energy change, so pyruvate needs to undergo the transitional step and be put into the Kreb's cycle before going back into phosphoenolpyruvate.
96. What is fatty acid catabolism? Calculate the number of ATP's produced by the breakdown of an 18-carbon fatty acid. Use my numbers rather than Fox's. The breakdown of an 18-carbon fatty acid will yield how many acetyl-CoA molecules? To make one acetyl-CoA , how many NADH and FADH2 are made? Each acetyl CoA then enters the Kreb's cycle. Each acetyl-CoA generates how many NADH, FADH2 , and ATP molecules? NADH and FADH2 then enter the Electron Transport Chain. Now calculate the total number of ATP generated from one 18-carbon fatty acid molecule. Compare to the ATP yield of one molecule of glucose? How many ATP's would be generated from a triglyceride containing three 18-carbon fatty acids?
Fatty Acid Catabolism: The breakdown of fatty acids.
For every 2 carbons in a fatty acid chain, one acetyl-coA can be made.
Each acetyl-coA can be converted into:
3 NADH (9 ATP)
1 FADH2 (2 ATP)
An additional NADH (3 ATP) and FADH2 (2 ATP) are produced for each time part of the fatty acid chain is made into acetyl-coA.
Ex. 18 C fatty acid
12(9)= 108 ATP
5(8)= 40 ATP
Total energy yield: 148 ATP
97. ATP is not stored. When ATP production exceeds need, acetyl-CoA is converted to fatty acid. Fatty acids are then combined with glycerol to make fat, ie. triglyceride. From where is the glycerol produced?
Glycerol is produced in the liver during glycolysis from either pyruvate or glucose.
98. What happens in oxidative deamination? What happens in transamination? The intermediates of the Kreb's cycle are ketoacids. What products are produced by these reactions? Why are these reactions important for energy metabolism? Can amino acids be converted to pyruvate? To intermediates in the Kreb's cycle? Which intermediates?
Oxidative deamination: Process by which amino acids can be converted into Kreb's intermediates and be put into the Kreb's cycle.
Amino Acid + Coenzyme => Keto Acid (intermediate) + Ammonia(NH3) + coenzyme
Transamination: Process by which Kreb's intermediates can be converted into amino acids.
Keto acid 2 + Amino Acid 1 => Keto acid 1 + amino acid 2
99. Can amino acids be used for ATP synthesis? How?
Amino acids can be incorporated into the Kreb's cycle as Krebs intermediates via oxidative deamination.
100. Can amino acids be used to produce glucose? How? (hint: get into the gluconeogenesis pathway)
Amino acids can be converted into pyruvate to be converted into oxaloacetate to be converted into phosphoenolpyruvate to be converted into glucose via gluconeogenesis.
101. Can amino acids be used to produce fatty acids? How?
Amino acids can be converted into pyruvate to be converted into acetyl-CoA during the transitional step to be converted into fatty acids (fatty acid synthesis).
102. Can glucose be used to produce fatty acids and ultimately fat. Yes! Describe how that happens.
Glucose goes through glycolysis and the transitional step to get acetyl-CoA which can be directly converted into fatty acids and then fat.
103. Can fatty acids be used to produce glucose? NO! Why not? Glucose that is not needed for ATP production goes straight to triglycerides (fat), but triglycerides (fat) cannot be converted to glucose no matter how badly the body needs glucose! This means if you ingest glucose in amounts exceeding your energy needs, the excess glucose is readily converted to fat. But if you need glucose, all your fat reserves (adipose tissue) cannot be converted back to glucose. Doesn't seem fair, does it?
Fatty acids can't be used to produce glucose because:
1) The conversion of pyruvic acid to acetyl-CoA is an irreversible reaction.
2) In the Kreb's cycle, the two carbons of an acetyl-CoA molecule are lost before any extra oxaloacetate is generated. Without any extra oxaloacetate, the making of glucose through the gluconeogenesis pathway cannot occur.
104. Define 'ligand' and 'substrate'.
Ligand: A molecule that binds to a receptor.
Substrate: A molecule in which an enzyme acts on.
105. What causes ligands and substrates to bind to proteins?
Ligands bind to proteins via ligand affinity. Enzymes will have active sites and electrostatic attractions that differ to accept specific ligands in a "lock and key" formation.
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