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USMLE
New FA Biochem 6
| Question | Answer |
|---|---|
| Name the complexes and important coenzymes and cytochromes in the electron transport chain. | 1. Complex I 2. Coenzyme Q 3. Complex III 4. Cytochrome C 5. Complex IV 6. Complex V |
| Where in the electron transport chain do NADH and FADH2 release their electrons? | Complex I |
| Where in the electron transport chain is O2 reduced to 2H2O? | Complex IV |
| Where in the electron transport chain is ADP converted to ATP? | Complex V aka ATP synthase aka mitochondrial ATPase |
| Name three classes of oxidative phosphorylation poisons. | 1. Electron transport inhibitors 2. ATPase inhibitors 3. Uncoupling agents |
| What is the mechanism of electron transport inhibitors? | 1. Directly inhibit electron transport causing: 2. Decreased protein gradient and decrease in O2 consumption, thereby: 3. Blocking ATP synthesis |
| What is the mechanism of ATPase inhibitors? | 1. Directly inhibit mitochondrial ATPase causing: 2. Increased protein gradient and increased oxygen consumption, but no ATP is produced because electron transport stops. |
| What is the mechanism of uncoupling agents? | "Uncouples" ATP synthesis from gradient production 1. Increase permeability of membrane 2. Proton gradient decreases, but oxygen consumption increases, as the gradient is not being maintained. 3. ATP synthesis stops, but electron transport continue |
| What is rotenone? | An electron transport inhibitor. |
| What is the mechanism of CN? | Electron transport inhibition |
| What is the mechanism of CO? | Electron transport inhibition |
| What is antimycin A? | An electron transport inhibitor. |
| What is the mechanism of oligomycin? | ATPase inhibition |
| What is the mechanism of thermogenin? | Uncoupling protein OR UCP which is an uncoupling agent |
| Where is thermogenin found? | Brown adipose tissue |
| What is the mechanism of 2,4-dinitrophenol? | Uncoupling agent |
| Name three uncoupling agents | 1. UCPs (such as Thermogenin) 2. 2,4-dinitrophenol 3. aspirin |
| Name the irreversible enzymes in gluconeogenesis, and where they are found. | Pathway Produces Fresh Glucose All the enzymes are found only in the liver, kidney, and intestinal epithelium 1. Pyruvate carboxylase in the mitochondria 2. PEP carboxykinase in the cytosol 3. Fructose-1,6-bisphosphatase in the cytosol 4. Glucose-6 |
| Name the irreversible enzymes in glycolysis. | 1. Hexokinase 2. Phosphofructokinase-1 3. Pyruvate kinase 4. Pyruvate dehydrogenase |
| What are the requirements of PEP carboxykinase? | GTP |
| Where does the pentose phosphate pathway happen? | Cytoplasm of Red Blood Cells, and in lactating mammary glands, liver, and adrenal cortex (all sites of fatty acid or steroid synthesis except RBCs) |
| How much ATP is used in the pentose phosphate shunt? | None |
| What are the main products of the pentose phosphate shunt and their uses? | 1. NADPH (for fatty acid and steroid synthesis, glutathione reduction, and cytochrome P-450) 2. Ribose-5-phosphate (for nucleotide synthesis) 3. G3P and F6P (glycolytic intermediates) |
| What are the key enzymes of the pentose phosphate shunt and are the reactions reversible or irreversible? | 1. Glucose-6-phosphate dehydrogenase (irreversible) 2. Transketolase (reversible) |
| What does transketolase require? | Thiamine (Vitamin B1) |
| What is the rate-limiting enzyme in the Pentose phosphate pathway? | Glucose-6-Phosphate Dehydrogenase |
| What is glutathione used for? | Detoxification of free radicals and peroxides. |
| What does NADPH deficiency in RBCs result in? | Hemolytic anemia |
| Name some oxidizing agents that someone with a G6PD deficiency is vulnerable to. | 1. Fava beans 2. Sulfonamides 3. Primaquine 4. Antituberculosis drugs |
| What protection does G6PD deficiency provide? | Protection against malaria |
| Which group is more likely to have G6PD deficiency? | Blacks |
| What are Heinz bodies? | altered Hemoglobin precipitates within RBCs, found in G6PD deficiency |
| What histologic change is seen in G6PD deficiency | Heinz bodies within red blood cells |
| What is the etiology of fructose intolerance? | 1. Lack of aldolase B 2. Build up of Fructose-1-Phosphate 3. Decrease in available phosphate 4. Inhibition of glycogenolysis and gluconeogenesis |
| What is the clinical presentation of fructose intolerance? | hypoglycemia, jaundice, cirrhosis, and vomiting |
| What is the difference in presentation between von Gierke's disease and fructose intolerance? | Both have hypoglycemia, jaundice, cirrhosis and vomiting. von Gierke's disease also has lactic acidosis whereas fructose intolerance does not. |
| What is the treatment for fructose intolerance? | Decreased intake of both fructose and sucrose. |
| What is the etiology of essential fructosuria? | Defect in fructokinase leading to lack of metabolism of fructose. Benign and asymptomatic |
| What is the clinical presentation of essential fructosuria? | Fructose appears in the blood and urine |
| Which is more serious, essential fructosuria or fructose intolerance? | Fructose intolerance, because it depletes the cells of phosphate. |
| What is the etiology of classic galactosemia? | 1. Absence of galactose-1-phosphate uridyl transferase 2. Build up of toxic substances including galactitol |
| What is the presentation of classic galactosemia? | Early: 1. Galactosemia 2. Galactosuria 3. Vomiting 4. Diarrhea 5. Jaundice Late: 1. Cataracts 2. Hepatosplenomegaly 3. Mental retardation |
| How does galactokinase deficiency present? | 1. Galactosemia 2. Galactosuria More severe symptoms such as cataracts, hepatosplenomegaly and mental retardation can follow. |
| What is the treatment for classic galactosemia? | Exclude galactose and lactose from the diet. |
| What enzyme converts galactose to galactitol? | Aldose reductase |
| What does aldose reductase do? | Converts galactose to galactitol |
| What enzyme converts Galactose to galactose-1-phosphate? | Galactokinase |
| What enzyme converts Galactose-1-Phosphate to Glucose-1-Phosphate? | Uridyl transferase |
| What enzyme converts UDP-galactose to UDP-glucose? | 4-epimerase |
| What does galactokinase do? | converts Galactose to galactose-1-phosphate |
| What does 4-epimerase do? | converts between UDP-galactose and UDP-glucose |
| What does Uridyl transferase do? | 1. converts UDP-glucose to UDP-galactose 2. converts Galactose-1-Phosphate to Glucose-1-Phosphate |
| What enzyme converts UDP-glucose to UDP-galactose? | Uridyl transferase |
| Which groups are more likely to be lactose intolerant? | 1. Blacks 2. Asians |
| What is the etiology of lactose intolerance? | Loss of brush-border lactase |
| How does lactose intolerance present? | 1. Bloating 2. Cramps 3. Osmotic diarrhea |
| What is the treatment for lactose intolerance? | Avoid milk or add lactase pills to the diet |
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Asclepius
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