Term
| Describe the conversion of glucose to pyruvic acid, and the reduction of NAD in glycolysis: |
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Definition
| It is when glucose (a 6-carbon sugar) is converted into 2 molecules of pyruvic acid. Each pyruvic acid molecule contains 3 carbons, 3 oxygens and 4 hydrogens (from glucose C6H12O6). 4 hydrogens are removed from the intermediates, and each pair is used to reduce 2 molecules of NAD, resulting in 2 molecules of NADH+H. This is the overall equation for glycolysis: Glucose + 2 NAD + 2 ADP + Pi---> 2 pyruvic acid + 2 NADH+H + 2 ATP |
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Term
| Describe how glycolysis results in 4 ATP molecules: |
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Definition
| The activation of glucose (needed to obtain energy) at the beginning of glycolysis requires the addition of 2 phosphate groups derived from 2 molecules of ATP (ATP-->ADP + Pi), this is phosphorylation. It is an "upstairs" motion, which is like an energy investment. After glucose is phosphorylated (and glucose is trapped within the cell) into glucose 6-phosphate from 1 ATP, another ATP is used to form glucose 6-phosphate into fructose 1,6-biphosphate. Then, it splits and the 6-carbon molecule is split into 2 3-carbon long molecules, which is phosphoglyceraldehyde. Then, 2 pairs of hydrogens are removed, and a phosphate is added, reducing 2 NAD into 2 NADH+H. This turns 3-phosphoglyceraldehyde into 1,3 biphosphoglygeric acid. Then, a phosphate is removed, turning each 1,3 biphosphoglygeric acid into 2 ATP and 2 molecules of 3-phosphoglyceric acid. Finally, after some isomerizations, the last phosphate group is removed from each intermediate, forming another 2 ATP (net gain of 2) and 2 molecules of pyruvic acid. |
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Term
| Describe the lactic acid pathway: |
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Definition
| This is when the NADH+H produced in glycolysis is oxidized by donating its electrons to pyruvic acid. This results in the re-formation of NAD, and the addition of 2 hydrogen atoms to pyruvic acid--reducing it. The addition of 2 hydrogen atoms to pyruvic acid produces lactic acid. |
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Term
| Describe the physiological significance of the lactic acid pathway: |
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Definition
| It is a type of anaerobic metabolism, meaning oxygen is not used in the process, and an organic molecule is the last electron acceptor. This yields a net gain of 2 ATP, and can only keep a cell alive as long as lactic acid concentrations are not excessive. |
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Term
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Definition
| It is the process in which glucose 6-phosphate (which is converted from pyruvic acid) in liver cells can be converted to free glucose that is secreted into the blood. It is the conversion of noncarbohydrate molecules through pyruvic acid to glucose. |
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Term
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Definition
| It is the process by which exercise turns glycogen into glucose 6-phosphate, which is then turned into pyruvic acid, which becomes lactic acid. This leaves the skeletal muscles, and enters the blood. Lactic acid enters the liver, then it and reverses back to pyruvic acid, glucose 6-phosphate, then leaves the liver as glucose. Glucose enters the blood, and then combined with rest, is converted back (interconverted) to glycogen in the skeletal muscles. |
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Term
| Describe the formation of acetyl CoA: |
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Definition
C6H12O6+O2--->6 CO2 + 6 H2O It begins with glycolysis, resulting in production of 2 molecules pyruvic acid, 2 ATP and 2 NADH+H per glucose molecule. However, the electrons in NADH+H are not donated to pyruvic acid, and lactic acid is not formed. The pyruvic acids move to a different location, and NADH+H are eventually oxidized. Pyruvic acid moves from the cytoplasm into a mitochondrion, and CO2 is enzymatically removed from each 3-carbon long pyruvic acid, which forms a 2-carbon long acetic acid. The enzyme that catalyzes the reaction combines acetic acid with a coenzyme called coenzyme A. The combination of coenzyme A with acetic acid forms acetyl coA. Coenzyme A acts only as a transporter of acetic acid from one enzyme to another. Since 1 glucose is converted into 2 molecules of pyruvic acid, 2 molecules of acetyl coA and 2 molecules of CO2 are thus derived from each glucose. Acetyl coA serves as a substrate for mitochondrial enzymes in the aerobic pathway while the CO2 is eliminated as waste. |
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Term
| Describe aerobic cell respiration of glucose through the Krebs cycle: |
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Definition
| Once acetyl coA is formed, the acetic acid subunit (2 carbons long) combines with the oxaloacetic acid (4 carbons long). This forms citric acid (6 carbons long). 2 hydrogens are donated from citric acid, and oxidizes NAD, forming NADH+H. CO2 is released as waste, which forms a-ketoglutaric acid (5 carbons long). Another CO2 is released, and another 2 hydrogens are donated from a-ketoglutaric acid, and oxidizes NAD, forming NADH+H. An H2O is added and GTP phosphorylates ADP into ATP, and 2 hydrogens are donated from succinic acid (4 carbons long) oxidizing FAD, forming FADH2. Succinic acid becomes fumaric acid (4 carbons long) which accepts H2O, becoming maltic acid (4 carbons long). This donates 2 hydrogens to oxidize NAD forming NADH+H, turning maltic acid into oxaloacetic acid (4 carbons long) completeing the turn of the Krebs cycle. |
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Term
| Describe the electron transport system: |
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Definition
| Built into the inner membrane of the mitochondrial cristae are a series of fixed molecules, which serve as the electron transport system. The chain of molecules consists of a protein, flavin mononucleotide (FMN), coenzyme Q and cytochromes (iron-caontaining pigments). They transport electrons from NADH+H and FADH2, which acts as an oxidizing agent for NAD and FAD. The oxidized forms of NAD and FAD are thus regenerated, shuttling electrons from the Krebs cycle to the electron transport chain. |
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Term
| Describe oxidative phosphorylation: |
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Definition
| When the electron transport system acts as an oxidizing agent for NADH+H and FADH2, each element in the chain functions as a reducing agent; one reduced cytochrome transfers its electron to the next cytochrome in the chain, alternatively reducing cytochromes (Fe3+ to Fe2+) and oxidizing (Fe2+ to Fe3+). This exergonic process uses the energy derived to phosphorylate ADP to ATP. The production of ATP through the coupling of this transport system with the phosphorylation of ADP is oxidative phosphorylation. |
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Term
| Explain the role of oxygen in the process of oxidative phosphorylation: |
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Definition
Oxygen is the final electron acceptor of the electron transport chain. It oxidizes cytochrome a3, which allows electron transport and oxidative phosphorylation to continue, because if the last electron remained in a reduced state, it wouldn't be able to accept any more electrons. This would end ATP production in the mitochondria and it could only continue anaerobically. At the very last step of aerobic respiration, oxygen becomes reduced by the 2 electrons that were passed down the chain from NADH+H and FADH2. This reduced oxygen binds 2 protons and an H2O molecule is formed-- O2 + 4e- + 4H+ ---> 2 H2O |
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Term
| Explain how glucose can be produced from glycogen, and how the liver produces free glucose for secretion: |
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Definition
| The enzyme glycogen phosphorylase catalyzes the breakdown of gycogen to glucose 1-phosphate, which is then converted to glucose 6-phosphate. This conversion is glycogenolysis. Glucose 6-phosphate cannot leak out of the cell, but the liver produces and enzyme called glucose 6 phosphatase, which removes the phosphate groups and produces free glucose, which can be secreted into the blood. |
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Term
| How can trigycerides be used in aerobic cell respiration? |
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Definition
| During the process of lipolysis, lipase enzymes hydrolyze trigycerides into glycerol and fatty acids. This results in free fatty acids, which are a long hydrocarbon chain with a carboxyl group on one end. In the process of b-oxidation, enzymes remove 2-carbon acetic acid molecules from the end of a fatty acid chain. This results in the formation of acetyl coA, as the third carbon from the end becomes oxidized to produce a new carboxyl group. Acetyl coA is then converted into citric acid in the Krebs cycle. |
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Term
| What is the nature of ketone bodies? |
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Definition
| If lipolysis exceeds the rate of fatty acid utilization, the blood concentration of fatty acids increase. If the liver contains sufficient amounts of ATP so that further production is not needed, some of the acetyl coA is channeled into an alternate pathway. This involves the conversion of 2 molecules of acetyl coA into 4-carbon long acetoacetic acid and b-hydroxybutyric acid. This, combined with acetone, forms ketone bodies. Increased production of ketone bodies may indicate signs of disease, such as diabetes. |
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Term
| How can amino acids be metabolized for energy? |
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Definition
| Many amino acids can be converted into glutamic acid by transanimation. Since glutamic acid can donate amine groupsto urea (through deanimation) it serves as a channel through which other amino acids can be used to produce keto acids (pyruvic acids and Krebs cycle acids). These keto acids and then be used in the Krebs cycle as an energy source. |
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Term
| Explain how proteins, fats and carbohydrates can be interconverted: |
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Definition
Trigycerides- convert to glycerol and fatty acids, which eventually can be converted to acetyl coA. Proteins- can be broken down into amino acids, which can then be converted into acetyl coA or be directly deanimated and go into Krebs cycle Carbohydrate- turns into pyruvic acid and then acetyl coA. Almost all conversions are reversible, but pyruvic acid to acetyl coA is not, because a CO2 was removed in the process. |
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Term
| In which tissue(s) is anaerobic metabolism normal? In which tissues is it abnormal? |
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Definition
| It is normal in the blood cells, because they only can use the lactic acid pathway (because they lack mitochondria). It is normal in skeletal muscles, up to a point, but when the ratio of oxygen supply to oxygen need falls below a critical lecel, and goes into "emergency mode" lactic acid accumulates and causes fatigue and pain. In the heart (which usually only respires aerobically) anaerobic respiration would be considered a real life-threatening emergency, and could only provide a small amount of ATP until oxgen deficeiency has passed. The brain can only function about 4 seconds anaerobically, then conciousness is lost. |
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Term
| Why can only the liver secrete glucose derived from its stored glycogen? |
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Definition
| Because only the liver contains glucose 6-phosphatase, that can remove the phosphate groups in glucose 6-phosphate, which keeps the glucose trapped within a cell. |
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Term
| Compare the fate of pyruvate in aerobic and anaerobic respiration: |
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Definition
In anaerobic respiration, pyruvic acid is reduced by the re-formation of NAD in the cytoplasm (if there is not sufficient oxygen). In aerobic respiration, pyruvic acid leaves the cytoplasm and enters the mitochondria, where CO2 is enzymatically removed from each 3-carbon long pyruvic acid to form a 2-carbon long acetic acid. This,, combined with coenzyme A, forms acetyl CoA, which activates the Krebs cycle. |
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Term
| Draw a simplified Krebs cycle and indicate the high energy products: |
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Definition
| The 3 NADH+H and 1 FADH2 are the high energy products, because they donate their electrons to an energy transferring process that results in the formation of a high number of ATP. |
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Term
| How do NADH+H and FADH2 contribute to oxidative phosphorylation? |
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Definition
| NADH+H and FADH2 become oxidized by transferring their pairs of electrons to the electron transport system of the mitochondrial cristae. The oxidized forms of NAD and FAD are regenerated and can continue to shuttle electrons from the Krebs cycle to the electron transport chain. |
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Term
| How is ATP produced in oxidative phosphorylation? |
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Definition
| The production of ATP is through the coupling of the electron-transport system and the phosphorylation of ADP (oxidative-phosphorylation). The electron transport system is powered by the transport of electrons, and it pumps protons from the mitochondrial matrix into the space between the inner and outer mitochondrial membranes. The electron transport system is grouped into 3 complexes that serve as proton pumps (the first puoms 4, second 4 and third 2). As a result, there is a higher concentration gradient in the intermembrane space than in the matrix, favoring the diffusion of H+ back into the matrix. The membrane can only permit diffusion of H+ through the respiratory assemblies. There is a stem serving as a channel and a globular subunit protruding into the matrix, containing ATP syntase, which catalyzes the reaction ADP + Pi--> ATP when it is activated by the diffusion of protons through the respiratory assemblies and into the matrix. This way, phosphorylation (addition of phosphate to ADP) is coupled to oxidation (transport of electrons) in oxidative phosphoylation. |
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Term
| Construct a flowchart to show the metabolic pathway by which glucose can be converted to fat: |
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Definition
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Term
| List 5 blood-borne energy carriers and explain, in general terms, how these are used as sources of energy: |
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Definition
| Glucose and ketone bodies that come from the liver, fatty acids from adipose tissue, lactic acids and amino acids from the skeletal muscles all can be converted into pyruvic acid or acetyl CoA, which can then enter the Krebs cycle and produce energy. |
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Term
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Definition
| It is when lipase enzymes hydrolyze triglycerides into glycerol and fatty acids. |
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Term
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Definition
| It is a type of reaction where a keto acid (such as pyruvic acid and Krebs cycle acids) are converted into amino acids by the addition of an amine group (NH2). This is usually obtained by "cannibalizing" another amino acid. In this process, a new amino acid is formed, as the one that was cannibalized is converted into a new keto acid. This functions in producing "nonessential" amino acids from "essential" amino acids(ones the body can't produce). |
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Term
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Definition
| If there are more amino acids than are needed for protein synthesis, the amine group can be removed and excreted as urea in the urine. Since an acid can donate amine groups to urea (through deanimation) it can serve as a channel through which other amino acids can be used to produce keto acids (pyruvic acids and Krebs cycle acids). These then can be respired for energy, converted to fat or converted to glucose (gluconeogenesis). |
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