Exam 2 Flashcards
Acetyl-CoA. a.) What is its structure? b.) What is its metabolic importance? c.) What is its source? Where does it come from?
- a.) see picture - b.) It is an important intermediate and precursor molecule for TCA, FA biosynthesis, ketone body formation and cholesterol biosynthesis (leading to steroid hormones, bile acids and vit D production) - c.) It is produced as a result of glycolysis, beta-oxidation and AA deamination/oxidation. It is requires presence of vitamin B5.
Pyruvate. a.) What is the fate of pyruvate? b.) What enzyme converts pyruvate to acetyl-CoA? c.) What enzyme converts pyruvate to oxaloacetate? d.) What determines whether pyruvate is used to form acetyl-CoA or oxaloacetate?
- a.) lactate, oxaloacetate, acetyl-CoA and alanine - b.) PDH complex - c.) pyruvate carboxylase - d.) pyruvate carboxylase is allosterically activated by acetyl-CoA. When there is sufficient amount of acetyl-CoA and therefore little need to divert more pyruvate into acetyl-CoA, pyruvate carboxylase converts pyruvate to oxaloacetate.
What is DNP? What is its effect? What symptoms does it cause?
- It is a pesticide and poison that uncouples ETC/ox-phos. It causes sweating, flushing, nausea, inc RR, tachycardia, fever, coma, death in 1-2 days. Treatment with ice baths, oxygen and fluid/electrolyte replacement.
Where are the following glucose transporters found? What are their functions?
- SGLT1: found in small intestine, responsible for actively transporting glucose from lumen into intestinal epithelia. - GLUT1: found in all tissues, responsible for basal glucose uptake - GLUT2: found in liver, intestine and beta-cells of pancreas. In liver: removes glucose from blood. In intestine: releases glucose from epithelia into blood. In pancreas: regulates secretion of insulin. Also able to move fructose. - GLUT3: found in all tissues, responsible for basal glucose uptake - GLUT4: found in muscle and adipose tissue. Increases with endurance training, induced by insulin. - GLUT5: found in small intestine, responsible for uptake of fructose into epithelial cells and movement into blood serum.
Which enzymes of gluconeogenesis are regulated? What factors inhibit and stimulate these enzymes? Which is the main regulated step? Which are reversible/irreversible?
- Pyruvate carboxylase: +: acetyl-CoA; -: insulin - PEP carboxykinase: +: glucagon via cAMP; -: insulin, AMP - Fructose-1,6-bisphosphatase: +: citrate; -: F26BP, AMP (main regulated step) - Glucose-6-phosphatase: +: glucagon; -: insulin
What is MEOS? Explain.
- Microsomal ethanol oxidizing system. This is a P450 cytochrome system that is induced in chronic alcohol abuse and has a higher capacity to process alcohol. Activation of this system causes oxidation of NADPH and weakens the cellular antioxidant defense mechanisms.
Explain how lipids are transported into the mitochondria. Is it in the form of TAGs or FAs?
- FAs are transported into the mitochondria.
Which intermediate during ketone body synthesis can function in another pathway (besides acetyl Co-A)? What pathway? During what environmental conditions will this occur?
- HMG-CoA = beta-hydroxy-beta-methylglutaryl-CoA - This molecule is used in the synthesis of cholesterol. - Will occur in well-fed times
What is the enzyme that commits acetyl-CoA to FA synthesis? What does this reaction do?
- Acetyl-CoA carboxylase, which converts acetyl-CoA to malonyl-CoA
Describe the synthesis of FAs.
Draw function of glucagon presence (insulin absence) in regulation of FA synthesis.
Describe the composition of lipid droplets?
- Lipid droplets are packages containing TAGs. These are surrounding by a protein coat composed of many proteins including perilipin. Perilipin acts as protector of the TAGs stores and prevents lipases, such as hormone sensitive lipases from degrading TAGs into FFA and glycerol. When perilipin is phosphorylated, it allows lipases to do this, but not when dephosphorylated.
What are the three factors that lead to development of fatty liver in chronic alcoholism?
1.) alcohol metabolism in liver generates NADH and acetyl-CoA. High concentration of NADH blocks TCA cycle enzymes and forces acetyl-CoA into FA synthesis. 2.) Beta-hydroxyacyl dehydrogenase (beta-oxidation enzyme) requires NAD, which is at low concentration during alcohol metabolism. This means that FA breakdown by liver is slowed down and leads to accumulation of fat. 3.) Damaged liver tissue has reduced capacity to synthesize VLDLs to export FAs to adipose tissue
Describe synthesis of prostaglandins, thromboxanes and leukotrienes.
1.) Prostaglandins - AA to PGG2 via COX1/2 - PGG2 to PGH2 via PGH synthase - PGH2 is precursor to other prostaglandins via PGD/PGE/PGF synthase enzymes 2.) Thromboxanes - PGH2 to TXA2 via thromboxane synthase - TXA2 to TXB2 via hydrolysis in blood 3.) Leukotrienes - AA to leukotrienes via lipoxygenase and other enzymes
How can prostaglandin synthesis be inhibited? Explain
- NSAIDs and glucocorticosteroids(aka glucocorticoids) inhibit COX1/2 and prostaglandin synthase (PGH synthase)
Name the sphingolipidoses. Name the enzyme defect, accumulated lipid and presentation.
1.) Tay-Sachs Disease Enzyme defect: beta-hexosaminidase A Accumulated lipid: ganglioside GM2 Presentation: mental retardation, blindness, cherry red spot on macula, death before age 3 2.) Gaucher Disease Enzyme defect: beta-glucosidase (beta-cerebrosidase) Accumulated lipid: glucocerebroside Presentation: liver and spleen enlargement, erosion of long bones 3.) Fabry Disease Enzyme defect: alpha-galactosidase Accumulated lipid: ceramide trihexoside Presentation: skin rash, kidney failure 4.) Niemann-Pick Disease Enzyme defect: sphingomyelinase Accumulated lipid: sphingomyelin Presentation: liver and spleen enlargement, mental retardation 5.) Sandhoff Disease Enzyme defect: beta-hexosaminodase A and B Accumulated lipid: GM2 ganglioside and globosides Presentation: similar to Tay-Sachs, progresses more rapidly 6.) Metachromatic Leukodystrophy Enzyme defect: arylsulfatase Accumulated lipid: sulfatide Presentation: mental retardation
Where is cholesterol synthesized, what is the rate-limiting step/enzyme, what is the precursor used, in what other pathway is this precursor seen? What enzyme is used to make this precursor? Is this the same enzyme used in the previous pathway? Explain. During what environmental conditions is the precursor made in both pathways?
- Cholesterol synthesis takes place in the liver, intestine and reproductive tissues - Rate-limiting step = HMG-CoA reductase - Precursor = HMG-CoA – seen during synthesis of ketone bodies - Precursor synthesized by cytosolic HMG-CoA synthase isoform that is active in well-fed state. Mitochondrial HMG-CoA synthase isoform synthesizes the precursor when in starving/fasting state.
How can cholesterol synthesis be inhibited in a clinical setting? Explain how this works.
- Use of statins - Statins inhibit the HMG-CoA reductase enzyme and prevents synthesis of mevalonic acid, a precursor molecule to farnesyl-PP, a precursor to cholesterol.
T2D patients present with high serum LDL even when serum glucose is well controlled. Where does this lipid abnormality originate? Why does it occur?
- Type 2 diabetics are insulin insensitive - As a result of insulin signaling stating to the body that glucose is in abundance and should be taken up, fatty acids are still being released from adipose tissue and the liver has to repackage large amounts of these, which in turn means that LDL levels are high.
What is the malate-aspartate shuttle? Where does it occur? Draw it.
- It is a shuttle mechanism to move electrons from NADH in cytoplasm to the mitochondrion. It occurs in liver and heart.
What are/is disorder(s) that prevent proper use of galactose? Explain.
- Galactosemia - Three types: a.) Classic galactosemia: most common / severe form where there is a galactose-1 phosphate uridyl transferase deficiency b.) Deficiency of galactokinase c.) Deficiency of UDP-galactose epimerase - Results in accumulation of galactose1-phosphate in liver and other tissues (CNS, kidney). Newborns present with milk intolerance and signs of liver failure, cataracts and intellectual disability. Also present with jaundice, lethargy and hepatomegaly. Diagnosis is by detection of galactose or galactose-phosphate in urine. Pts must receive a galactose-free diet (no lactose either, which is a glucose, galactose disaccharide).
Explain how F26BP affects gluconeogenesis. Include details about the enzymes involve, pathways activated and substrates affected.
- Take home message: high concentrations of F26BP inhibit gluconeogenesis, low concentrations of F26BP stimulate gluconeogenesis - F26BP is produced by enzyme PFK2 (produces F26BP from F6P) - Insulin stimulates PFK2 via cAMP leading to increased concentration of F26BP, which causes inhibition of gluconeogenesis via pyruvate carboxylase, PEP carboxykinase and glucose-6-phosphatase - Glucagon inhibits PFK2 via cAMP leading to decreased concentration of F26BP, which causes stimulation of gluconeogenesis via PEP carboxykinase and glucose-6-phosphatase
Explain why NADH concentration increases while NADPH concentration decreases in alcohol-metabolizing cells.
- The main step to handling ethanol in the liver is through two dehydrogenases (alcohol DH and aldehyde DH), both, which produce NADH. - The other way to handle ethanol is through the higher capacity MEOS system, which as a means to process the alcohol, also oxidizes NADPH.
List a few mucopolysaccharidoses. Describe defect and symptoms. Genetics?
- Hunter’s: defect in iduronate sulfatase, accumulation of dermatan sulfate and heparan sulfate. Symptoms = skeletal abnormalities, mental retardation. X-linked recessive. - Hurler-Scheie: defect in alpha-iduronase, accumulation of dermatan sulfate and heparan sulfate. Symptoms = skeletal abnormalities, mental retardation. Autosomal recessive. - Sanfilippo’s: defect of heparan sulfate degradation. Symptoms = mild physical defects, severe mental retardation. Autosomal recessive.
Why aren’t ketone bodies used in liver or kidney?
- These tissues don’t express acetoacetate:succinyl-CoA transferase to generate the intermediate: acetoacetyl-CoA that generates acetyl-CoA.
Describe important of asymmetric distribution of lipids between lipid bilayers. What is typical distribution? Implication in RBCs
- Outer leaflet is rich in PC and sphingomyelin (both have choline) - Inner leaflet is rich in PE and PS - Stress activates enzymes known as flippases that flips lipids between leaflets - Eg. When PS appears in outer leaflet of RBCs, RBCs are destroyed by macrophages.
What are the function of leukotrienes?
- promotion of SM contraction - anaphylaxis
What enzyme(s) require(s) thiamin (B1)?
- Alpha-ketoglutarate dehydrogenase complex and PDH complex.
Explain what reaction(s) the cell can perform when there is a need for NADPH and ATP. Ribose is not required.
Explain the effect of insulin-induced dephosphorylation on glycogen phosphorylase and glycogen synthase.
- Glycogen phosphorylase is inactivated - Glycogen synthase is activated
Explain process of beta-oxidation. Include enzymes, substrates, cofactors and products.
Draw function of insulin in regulation of FA (TAG) synthesis.
Describe role of chylomicron, where synthesized, association with apoproteins, source of apoproteins, destination of contents and formation / fate of chylomicron remnant.
What is biotin? Which vitamin is it?
- Biotin is a B vitamin, also known as vitamine B7. It is required by pyruvate carboxylase.
Describe how xenobiotics are detoxified.
- Example: acetaminophen. - UGT catalyzes conjugation of UDP-glucuronate with acetaminophen, making it water soluble, allowing it to be excreted in urine
How does carnitine deficiency present? What are the consequences?
- Without carnitine, FAs cannot be imported into mitochondria to be used as energy source. - Pts present as fasting non-ketotic hypoglycemia. Ketones are unusually low in blood or / and urine.
Describe synthesis and sulfation of glycosaminoglycans.
- Core proteins are manufactured in ER - Transferred to Golgi where glycosyltransferases add disaccharides to them. - Sulfotransferases add sulfate groups to them (can be unpredictable) - Exported in membrane-bound vesicle, finds linker and attached to polysaccharide backbone
List endogenous uncoupling proteins. What are their functions?
- UCP1-4. These are found in brown fat, skeletal muscle, brain and other parts of the body and function to increase body temperature.
Describe/draw the reactions of glycogen degradation (glycogenolysis).
Explain the process of FA elongation from a 16 carbon molecule. Why is this necessary? Where does it occur?
- Cytoplasm has FA synthase that synthesizes FAs to 16 carbons = palmitate (16:0), which is a saturated molecule. - Many lipid structures in the body are longer than 16 carbons - Elongation occurs in mitochondrial as shown here:
Explain the process of FA desaturation. Why is this necessary? Where does it occur?
- Many lipids in body are not saturated. - Desaturation of FAs occur in endoplasmic reticulum as shown here:
What are the precursors for gluconeogenesis?
- Lactate, - Amino acids - Glycerol
What are the products of the non-oxidative phase of the pentose phosphate pathway? Why are these important?
- 2 F6P and 1 glyceraldehyde-3-phosphate - These are intermediates in the glycolytic / gluconeogenic pathways and can be synthesized from pentoses depending on the need of the cell.
Describe the clinical presentation of pyruvate kinase deficiency.
- In this disorder, RBCs are deprived of ATP (only get 1 ATP instead of 2 from glycolysis), which leads to lysis of the cells (chronic hemolytic anemia) because the membrane potential cannot be maintained. These patients present at pale, jaundiced, fatigued, SOB, tachycardic. They have splenomegaly, excess of iron in blood and have gallstones. Severe cases require pts to have regular blood transfusions.
Draw the glycolytic pathway. Include all the enzymes, where ATP is made or used and where reducing equivalents are produced.
Describe the effect of arsenic on glycolysis.
- Arsenic mimics phosphate. In its presence, Glyceraldehyde-3-phosphate DH reaction yields arsenic product instead of 13BPG. The arsenic product is unstable and hydrolyzes to 3PG. No ATP is gained from the process, where previously the conversion to 3PG yields a single ATP. Net ATP from glycolysis with one molecule of glucose is 0. This is problematic for RBCs who rely solely on glycolysis for their energy production. - Pts present with SOB and dizziness. CBC reveals hemolytic anemia and elevated urine arsenic levels. Treatment includes discontinuation of arsenic and therapeutic red-cell exchange.
Examples of exogenous uncouplers to ETC/ox-phos. Symptoms? Treatment?
- DNP (2,4 dinitrophenol) is a pesticide and poison. It causes sweating, flushing, nausea, inc RR, tachycardia, fever, coma, death in 1-2 days. Treatment with ice baths, oxygen and fluid/electrolyte replacement. - Aspirin in very high doses
Describe role of VLDL, IDL and LDL. Include where each are synthesized/formed, association with apoproteins, source of apoproteins, destination of contents and fate of lipoprotein.
Briefly explain the role of F26BP in gluconeogenesis and glycolysis.
- High F26BP concentrations: glycolysis is stimulated, gluconeogenesis is inhibited - Low F26BP concentrations: glycolysis is inhibited; gluconeogenesis is stimulated
What is the function of diacylglycerol acyltransferase (DGAT) inhibitors?
- Inhibits synthesis of triacylglycerol
How do gallstones form?
- Bile contains cholesterol, bile salts and phospholipids. These aid in emulsification of dietary fats. Cholesterol is prone to precipitating in gallbladder and duct works as its water solubility is low. When in high concentration, it particularly precipitates out causing formation of cholesterol stones known as gallstones, which can obstruct the gallbladder and ducts causing painful backup of bile of pancreatic enzymes.
Describe/Draw how fructose is degraded.