human nutrition exam 3
The other B 12 -requiring enzyme is methionine synthase see the Cysteine Synthesis section above. Aspartate can be formed in a transamination reaction or via the deamination of asparagine. Lipogenesis creates triglycerides from excess carbohydrates, proteins, and fats, which are stored during the later stages of the fasting state. This enzyme is a member of the family of one-carbon transferases and is also known as glycine hydroxymethyltransferase. The primary role of many B-vitamins is to act as coenzymes in metabolic processes. Phenylalanine serves as the precursor for tyrosine. Asparagine is synthesized from aspartate via an amidotransferase reaction catalyzed by asparagine synthetase.
Its mechanism of action is not clearly understood but probably involves inhibition of VLDL secretion, which in turn decreases the production of LDL. Patient reported no rash or skin changes. A definitive molecular defect has not been established. There are four enzyme complexes involved in the electron transport chain. Immediately following experimental hypothalamic damage in rodents, insulin secretion and autonomic nervous system stimulation of fat cells increase, redirecting calories to fat tissue at the expense of lean body mass before overeating has developed [ Friedman , Bray , Penicaud ]. Published December 6, By Dr.
He was without complaints and was feeling well on his subsequent follow-up visit. On repeat serum cholesterol screening, a decrease in the cholesterol level was noted. The patients had an episode of IHD Ischemic heart disease , and had hyperlipidemia.
Hyperlipidemia is one of the most treatable risk factors of coronary heart disease. Initially, when the fasting low-density lipoprotein LDL cholesterol is found elevated, life style modification is recommended such as dietary adjustments, exercise, and weight loss. If the LDL cholesterol level is again found above threshold, pharmacological therapy is initiated.
Since the patient in the given case had a mild attack of IHD, hence without trial he had been put on low-fat diet and statins. Virtually all tissues containing nucleated cells are capable of cholesterol synthesis, which occurs in the endoplasmic reticulum and the cytosol. LDL-C is a transporter of cholesterol from liver to peripheral tissues, while HDL is a transporter of cholesterol from peripheral tissues to liver for degradation. Atherosclerosisis characterized by the deposition of cholesterol and cholesteryl ester fromthe plasma lipoproteins into the artery wall.
HDL cholesterol ratio a good predictive parameter. This is consistent with the function of HDL in reverse cholesterol transport. Plant oils such as corn oil and sunflower seed oil contain a high proportion of polyunsaturated fatty acids, while olive oil contains a high concentration of monounsaturated fatty acids. On the other hand, butter fat, beef fat, and palm oil contain a high proportion of saturated fatty acids.
Sucrose and fructose have a greater effect in raising blood lipids, particularly triacylglycerols, than do other carbohydrates. The reason for the cholesterol-lowering effect of polyunsaturated fatty acids is still not fully understood.
It is clear, however, that one of the mechanisms involved is the up-regulation of LDL receptors by poly- and monounsaturated ascompared with saturated fatty acids, causing an increase in the catabolic rate of LDL, the main atherogenic lipoprotein. In addition, saturated fatty acids cause the formation of smaller VLDL particles that contain relatively more cholesterol, and they are utilized by extrahepatic tissues at a slower rate than are larger particles—tendencies that may be regarded as atherogenic.
Additional factors considered to play a part in coronary heart disease include high bloodpressure, smoking, male gender, obesity particularly abdominal obesity , lack of exercise, and drinking soft as opposed to hard water.
Premenopausal women appear to be protected against many of these deleterious factors, and this is thought to be related to the beneficial effects of estrogen. There is an association between moderate alcohol consumption and a lower incidence of coronary heart disease. It has been claimed that redwine is particularly beneficial, perhaps because of its content of antioxidants. Few of the commonly used drugs to lower cholesterol level are as follows-.
A family of drugs known as statins, have proved highly efficacious in lowering plasma cholesterol and preventing heart disease. These molecules mimic the structure of the normal substrate of the enzyme HMG-CoA and act as transition state analogues.
While the statins arebound to the enzyme, HMG-CoA cannot be converted to mevalonic acid, thus inhibiting the whole cholesterol biosynthetic process.
Effective treatment with Lovastatin, along with low fat diet, decreases levels of blood cholesterol. The lowering of cholesterol also lowers the amounts of the lipoproteins that transport cholesterol to peripheral tissues i.
Side effects of therapy — The potential side effects include elevated liver function tests,increased muscle creatine phosphokinase CPK secondary to Myopathy and rarely rhabdomyolysis. Its mechanism of action is not clearly understood but probably involves inhibition of VLDL secretion, which in turn decreases the production of LDL.
Niacin inhibits the release of free fatty acids from adipose tissue which leads to a decrease of free fatty acids entering the liver and decreased VLDL synthesis in the liver. Ezetimibe belongs to the azetidinone class of cholesterol absorption inhibitors. To maintain the bile acid pool size, the liver diverts cholesterol to bile acid synthesis. The decreased hepatic intracellular cholesterol content results in up regulation of the LDL receptor and enhanced LDL clearance from the plasma.
Fish oils can result in an increase in plasma LDL-C levels in some patients. Fish oil supplements can be used in combination with Fibrates,niacin, or statins to treat hypertriglyceridemia.
In general, fish oils are well tolerated and appear to be safe, at least at doses up to 3—4 g. A lower dose of omega 3 about 1 g has been associated with reduction in cardiovascular events in CHD Chronic Heart Disease patients and is used by some clinicians for this purpose. A year-old female at 32 weeks of gestation presented to the clinic with complaints of generalized itching.
Patient reported no rash or skin changes. She denied any change in detergent, soaps, or perfumes. She denied nausea and vomiting. There was no history of any drug intake or previous allergies. There was no fever or any other medical illness. On physical examination, there were no rashes apparent on her skin and only some excoriations were there from itching.
The patient is most probably having intrahepatic cholestasis ofpregnancy. High alkaline phosphatase is a marker of cholestasis. It is also high late in normal pregnancy due to the influx of placental alkaline phosphatase, But in cholestasis the level may be 4 times the normal reference range. Slightly high transaminases differentiate it from viral hepatitis in which very high levels are found and the high levels In the present case are due to bile salts induced toxic damage to the liver cells.
Bilirubin is high due to intrahepatic obstruction as a result of cholestasis. This is conjugated type. Increased serum bile salts and accumulation of bile salts in the dermis of the skin are responsible for generalized itching.
Cholestasis of pregnancy is a condition in which the normal flow of bile from the gallbladder is impeded, leading to accumulation of bile salts in the body. Bile salt molecules secreted by the gallbladder are essential for the emulsification and absorption of fats.
Bile salts perform important functions and are recycled by the body. The body produces mg of bile salts per day from cholesterol; this represents the fate of half of the cholesterol used daily in metabolism mg. Bile salts are produced in both the fetal and maternal liver. The fetus transfers the bile salts across the placenta for disposal.
When the function of the maternal gallbladder is slowed, bile salts can accumulate in the liver and bloodstream, ultimately resulting in the classical pruritus symptoms. It is believed that pregnancy-related hormones may slow bile salt excretion from the gallbladder.
It is speculated that the hormones such as estrogen and progesterone, which are elevated in pregnancy, cause a slowing of the gallbladder function, leading to this disorder.
Generalized pruritus is the main symptom of intrahepatic cholestasis of pregnancy. The itching may be more intense over the palms and soles but can extend to the trunk, extremities,eyelids, and, in rare cases, the oral cavity.
The pruritus is worse at night. The serum bilirubin levelis usually lower than 6 times the upper limit of reference range and is usually conjugated. Steatorrhea may be present, which may lead to deficiency of fat-soluble vitamins, especially vitamin K. Interestingly, gamma-glutamyltranspeptidase levels are within the reference range or only mildly elevated. Liver biopsy is rarely needed for diagnosis but reveals cholestasis with minimal hepatocellular necrosis. Medical treatment is directed at relieving maternal symptoms and improving fetal outcome.
Pruritus can be controlled with antihistaminics, and ursodeoxycholic acid. More severe cases may require bile salt binders such as Cholestyramine or corticosteroids. Fetal outcome is improved with early diagnosis and prompt treatment. Ursodeoxycholicacid is recycled through the enterohepatic circulation.
It is an oral medication that binds bile salts in the intestine and promotes their excretion in the feces. As this drug is not absorbed, it most likely has little effect on the fetus. Effects on the fetus are still under evaluation. In rare cases, drug-induced vitamin K deficiency is believed to contribute to hemorrhages during childbirth. Hypertriglyceridemia in Type I Diabetes Mellitus. Published December 6, By Dr. Deficiency in apoprotein C-II B.
Increased hepatic triglyceride synthesis C. Decreased lipoprotein lipase activity D. Deficiency in LDL receptors E.
Absence of hormone-sensitive lipase. Lipoprotein lipase Occurrence Lipoprotein lipase is located on the walls of blood capillaries, anchored to the endothelium by negatively charged proteoglycan chains of Heparan sulfate.
Figure Action of lipoprotein lipase LpL. Hypertriglyceridemia in Type 1 Diabetes Mellitus Dyslipidemia is a common metabolic abnormality in uncontrolled diabetes mellitus. Biochemical basis of dyslipidemia in uncontrolled DM One major role of insulin is to stimulate the storage of food energy following the consumption of a meal. Increased fatty acid oxidation Normally, the levels of malonyl-CoA are high in the presence of insulin.
Basis of hypertriglyceridemia Normally, plasma triglycerides are acted upon by lipoprotein lipase LPL. Clinical pearls In type 1 diabetes, moderately deficient control of hyperglycemia is associated with only a slight elevation of LDL cholesterol and serum triglycerides and little if any change in HDL cholesterol. As regards other options Deficiency in apoprotein C-II Apo CII is an activator of lipoprotein lipase, but its concentration is not decreased in diabetes mellitus.
Increased hepatic triglyceride synthesis The Acetyl Co A carboxylase, the key regulatory enzyme of fatty acid biosynthetic pathway, is activated by insulin, thus, de novo fatty acid synthesis is decreased in insulin deficiency. Deficiency in LDL receptors LDL receptors internalize LDL, their deficiency cannot cause hypertriglyceridemia, and otherwise also, they are not deficient in diabetes mellitus.
Absence of hormone-sensitive lipase Hormone- sensitive lipase catalyzes the breakdown of triglycerides in adipose cells. Published September 27, By Dr. The correct answer is- D — Oxaloacetate. Two facts demand attention here- 1 TCA cycle suppression and 2 Basis of ketogenesis In Diabetes mellitus, TCA cycle is in a state of suppression due to diminished availability of oxaloacetate which is channeled towards the pathway of gluconeogenesis.
Acetone, acetoacetate and beta hydroxy butyrate are the three ketone bodies d Accumulated ketone bodies, being acidic in nature and also as they deplete the alkali reserve cause acidosis.
As regards other options: Published July 9, By Dr. Case Details A 40 -year-old man presents with chest pain that radiates to his left jaw and shoulder. The correct answer is B- Mevalonate. Basic concept Biosynthesis of cholesterol The biosynthesis of cholesterol may be divided into five steps: HMG Co A reductase is inhibited by Statins by the mechanism of competitive inhibition and by bile acid, cholesterol and Mevalonate by feedback inhibition Significance The synthesis of Mevalonate is the committed step in cholesterol formation.
The newly formed cyclized structure is Lanosterol. Finally, the double bond of the side chain is reduced, producing cholesterol. Figure Steps of cholesterol biosynthesis As regards other options A. Geranyl pyrophosphate C10 is formed by condensation of Isopentenyl pyrophosphate and Dimethyl allyl pyrophosphate D. For further reading- Follow the link http: Rate limiting enzyme of fatty acid biosynthesis.
Published July 5, By Dr. Case details A year-old pregnant woman has a sugar craving and consumes a hot fudge sundae. It is activated by carboxylation B. It catalyzes a reaction that condenses an acetyl group with malonyl group C. It catalyzes a reaction that requires biotin and ATP D. It is activated by malonyl Co A. Basic concept Acetyl co A carboxylase is the first enzyme of fatty acid biosynthesis that catalyzes the carboxylation of Acetyl co A to Malonyl CoA.
Excessive carbohydrate ingestion promotes triglyceride synthesis through following mechanisms- 1 Glycolysis yields pyruvate and hence Acetyl coA which is a precursor for fatty acid biosynthesis. Malonyl co A, the product of this reaction inhibits this enzyme by feedback inhibition. Impaired beta oxidation of fatty acids. Published July 1, By Dr. Case details An infant presents with lethargy, sweating, and irritability.
Fatty acid synthase B. Acyl co A dehydrogenase C. Enoyl Co A hydratase D. Thiolase The correct answer is- Acyl co A dehydrogenase. As regards other options Fatty acid synthase is a multienzyme complex involved in fatty acid synthesis. Case study- Carnitine deficiency.
Published January 15, By Dr. Published January 5, By Dr. Case Details A 6-year- old child with progressive hearing loss wasbrought for consultation. What is the defectin this disease? Refsum disease Refsum disease RD is a neurocutaneous syndrome that is characterized biochemically by the accumulation of phytanic acid in plasma and tissues. Biochemical defect Refsum disease is an Autosomal recessive disorder characterized by defective alpha-oxidation of phytanic acid.
Metabolism , catabolism , anabolism. Metabolic pathway Metabolic network Primary nutritional groups. Pentose phosphate pathway Fructolysis Galactolysis. Photosynthesis Anoxygenic photosynthesis Chemosynthesis Carbon fixation. Fatty acid degradation Beta oxidation Fatty acid synthesis. Steroid metabolism Sphingolipid metabolism Eicosanoid metabolism Ketosis Reverse cholesterol transport. Amino acid synthesis Urea cycle. Purine metabolism Nucleotide salvage Pyrimidine metabolism.
Metal metabolism Iron metabolism Ethanol metabolism. Retrieved from " https: Amino acids provide energy at a steady pace throughout the fasting state. Beta-oxidation is a series of metabolic reactions in which amino acids are oxidized to yield energy.
Glucogenic amino acids are used to produce glucose through gluconeogenesis during the fasting state. Protein metabolism is halted during the fasting state. Which of the following statements correctly describes carbohydrate metabolism during the fasting state?
Muscle glycogen stores are depleted early in the fasting state. Liver glycogen stores are utilized to supply the blood with glucose even during long-term fasting.
In the later stages of the fasting state, fatty acids can be converted to glucose to supply the brain and red blood cells with fuel. Excess glucose is converted to a fatty acid, attached to a glycerol backbone, and stored as a triglyceride in adipose tissue in the fasting state.
Which of the following statements correctly describes lipid metabolism during the fasting state? Lipogenesis creates triglycerides from excess carbohydrates, proteins, and fats, which are stored during the later stages of the fasting state. Ketogenesis is stimulated by the breakdown of stored muscle glycogen during the early stages of the fasting state.
Fatty acids are rapidly broken down from adipose tissues and converted to ketone bodies during the later stages of the fasting state. During long-term starvation, ketone bodies can be used by the red blood cells but not by the brain, which relies on glucose produced by gluconeogenesis.
Which vitamin can increase absorption of non-heme iron? Which of the following statements applies to BOTH fat-soluble and water-soluble vitamins? Both classes contain essential nutrients. Both classes are easily excreted in urine. Both classes are readily stored so only need to be consumed weekly or monthly.
Both classes are naturally occurring inorganic substances. E ; tocopherols B. C ; antioxidants C. D ; tocopherols D. Which of the following foods contain s primarily non-heme iron? What is an advantage of obtaining nutrients from foods rather than supplements?
Vitamins in supplements are never absorbed into the bloodstream. Eating nutrients in food is the only way to correct a deficiency. Junk food can be converted to health food if vitamin C is added. Foods can provide a wide variety of nutrients, phytochemicals, and other dietary factors. Most minerals are absorbed better from animal food sources than from supplements. Fat-soluble vitamins should be consumed more frequently than water-soluble vitamins. Since vitamins are found in a wide variety of foods, they are considered non-essential.
Even individuals who eat a variety of healthy foods cannot meet their micronutrient needs from food alone and should take a daily supplement.
Enriching a low-nutrient food with a few vitamins does not turn it into a health food. In general, it is much easier to develop a toxic overload of nutrients from supplements than from foods. Most minerals are better absorbed from supplements than from animal food sources. Recent research has shown that high potency supplements may actually increase rates of death. Which of the following foods are NOT significant sources of vitamin A? Which of the following would be the best source of vitamin D?
Susan had a salad made of dark, leafy greens, oil and vinegar dressing, and cheese. Which of the following vitamins would NOT be found in adequate quantities from this lunch?
Patrick wants to increase his intake of vitamin E. Which of the following foods would provide him with a significant amount of vitamin E? Which of the following foods is considered a poor source of fat-soluble vitamins? Which of the following would be a significant source of potassium? Which of the following would be the best source of calcium? Susan consumed a significant amount of which of the following minerals?
Patrick wants to increase his intake and absorption of iron. He knows that heme iron is absorbed better than non-heme iron. Which of the following foods would provide him with highest amount of heme iron? Which of the following foods is a significant source of non-heme iron? Which of the following would NOT be a significant source of vitamin C? Which of the following would be the best source of vitamin B12?
Susan had a sandwich made with white bread, chicken, dark, leafy greens, and tomatoes. Which vitamins did she consume in significant amounts? All of these are correct. Patrick wants to increase his intake of niacin. Which of the following foods would provide Patrick with a significant amount of niacin? Which of the following foods is a significant source of riboflavin? Which of the following minerals is linked with energy metabolism?
Which of the following minerals is linked with fluid and electrolyte balance? Which of the following minerals is linked with antioxidant function? Which of the following minerals is linked with blood health?
Which of the following minerals is linked with bone health? Which of the following is a common characteristic of ALL vitamins and minerals? They provide no kcalories for the body. They are made up of organic molecules. They are all water soluble. They are destroyed with the cooking of food.
Which of the following is a characteristic of vitamins but NOT minerals? Vitamins tend to have low rates of absorption, while minerals absorb easily. Vitamins can be toxic to the body but minerals cannot. Vitamins provide kcalories for the body, while minerals do not. They can be either water or fat soluble. Which of the following is a characteristic of minerals but NOT vitamins? Minerals frequently function as coenzymes to energy metabolism enzymes, while vitamins are needed for fluid balance.
Minerals are inorganic molecules, while vitamins are organic. Minerals tend to have very high rates of absorption from the gastrointestinal tract, while vitamins are absorbed poorly. Minerals are needed in very small amounts each day, while vitamins are needed in relatively large amounts.
Which of the following vitamins is linked with energy metabolism? Which of the following vitamins is linked with the immune system? Which of the following vitamins is linked with antioxidant function? Which of the following vitamins is linked with bone health? Which of the following vitamins is responsible for red blood cell production?
With nine B-vitamins to choose from, the body almost always has enough of one or two of them to support metabolism. The primary role of many B-vitamins is to act as coenzymes in metabolic processes. B-vitamins are important to synthesize adequate homocysteine. B-vitamins provide the most energy of any of the micronutrients.
Which of the following individuals would be MOST likely to benefit from thiamin supplementation? Which of the following is NOT a good source of niacin? The hypothesis that poor B-vitamin status will reduce physical ability has NOT been supported by research. The FDA mandates the enrichment of refined grains with some of the nutrients lost in the milling process.
Iamges: de novo lipogenesis anabolic or catabolic
Eat more green vegetables. Mutations in the MUT gene are one of the causes of the methylmalonic acidemias.
Pregnant women require less nitrogen than they excrete. Within the small intestine there are two principal pancreatic enzymes involved in protein digestion; trypsin and chymotrypsin. The anionic amino acid transporters were also referred to as the system X transporters.
Glycolysis occurs in the cytoplasm of the cell. The MAT1A gene is located on chromosome 10q Chylomicrons are similarly metabolized and are converted to chylomicron remnants after the action of lipoprotein lipase nkvo, which are diana boldrini parravicini mondomostre through remnant receptors Apo E receptors in to the liver. The enzyme methylmalonyl-CoA databolic also requires B 12 and so a de novo lipogenesis anabolic or catabolic resulting from a deficiency in this vitamin is also associated with methylmalonic academia. It is a carbon-carbon condensation, an energy requiring process.
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