Lipids
Question 1. Classify lipids, and give examples. Give an account of essential fatty acids. (or) Classification of lipids with two examples for each. (or) Essential fatty acids
Answer:
Lipids:
Lipids are organic substances relatively insoluble in water, soluble in organic solvents, actually or potentially related to fatty acids, and utilized by living cells.
Classification:
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Essential fatty acids:
Definition:
The fatty acids that cannot be synthesized by the body and therefore, should be supplied in the diet are known as essential fatty acids.
Chemical nature:
- They are polyunsaturated fatty acids.
- They are linoleic acid and linolenic acid.
Functions:
Required for
- Membrane structure and function
- Transport of cholesterol
- Formation of lipoproteins
- Prevention of fatty liver
- Synthesize of eicosanoids.
Structure:
Deficiency:
- The deficiency of essential fatty acids leads to phrynoderma or toad skin.
- Its clinical features are:
- Horny eruptions on the posterior and lateral parts of limbs, on the back and buttocks.
- Loss of hair.
- Poor wound healing.
Question 2. Give an account of the beta-oxidation of fatty acids and mention its energetic, (or) Explain beta-oxidation of fatty acids. What is the importance of this process, (or)
Describe in detail the beta-oxidation of fatty acids. Indicate the sites at which ATPs are formed. (or) Write in brief on the β-oxidation of palmitic acid. Name the other types of fatty acid oxidation. Add a note on the functions of cholesterol. (or) Beta oxidation of saturated fatty acids
Answer:
Beta-oxidation of fatty acids:
Definition:
- It is the oxidation of fatty acids on the p-carbon atom.
- It results in the sequential removal of a two-carbon fragment, acetyl CoA.
Stages:
β-oxidation involves three stages.
1. Fatty acid activation:
- It occurs in two steps.
- Fatty acid reacts with ATP to form acyl adenylate
- Acyladenylate combines with coenzyme A to produce acyl CoA.
- The enzyme involved in it is thiokinase or acyl CoA synthetases.
- In it, two high-energy phosphates are utilized.
- ATP is converted to pyrophosphate.
- Pyrophosphate is hydrolyzed to phosphate by inorganic pyrophosphatase.
Fatty acid + ATP → acyl adenylate
Acyladenylate + coenzyme A → acyl CoA
2. Transport of acyl CoA:
- And a group of acyl CoA is transferred to carnitine by carnitine acyltransferase I on the outer surface of the mitochondrial membrane.
- Next, this acyl-carnitine is transported across the membrane to the mitochondrial matrix.
- On the inner surface of the mitochondrial matrix, carnitine acyl transferase II converts acylcarnitine to acyl CoA.
3. β-Oxidation proper:
- The cycle continues till fatty acids are completely oxidized.
Energetics:
- Palmitoyl CoA undergoes 7 cycles of p-oxidation to yield 8 acetyl CoA.
- Actyl CoA can enter citric acid cycle.
Importance:
- It results in the removal of acetyl CoA.
- This acetyl CoA can enter into the TCA cycle.
- It occurs in most of the tissues in the body.
- It continues till the fatty acid is completely oxidized.
- It occurs predominantly in biological systems.
- Its main aim is to generate energy.
- It produces metabolic water which has great importance in animals like camels and kangaroo rats.
- Due to metabolic water, these animals can live for long periods even without food and water.
Question 3. Write in brief on the β-oxidation of palmitic acid. Name the other types of fatty acid oxidation. Add a note on the functions of cholesterol. (or) Cholesterol (or) Functions of cholesterol.
Answer:
β-Oxidation:
Types of fatty acid oxidation:
1. β-oxidation of fatty acids in peroxisomes.
- Occurs in eukaryotic cells.
- In it, acyl CoA dehydrogenase leads to the formation of FADH2.
- 9 The reducing equivalent from FADH2 reacts with O2.
- Results in the formation of H2O2
- .This H2O2 is cleared by the catalase enzyme.
- Acyl CoA dehydrogenase \(\stackrel{\text { Leads to }}{\longrightarrow} \mathrm{FADH}_2\)
- Reducing equivalent FADH2 + O2→
Reducing equivalent FAD + H2O2 - \(\mathrm{H}_2 \mathrm{O}_2 \stackrel{\text { Catalase }}{\longrightarrow} \mathrm{H}_2 \mathrm{O}+\frac{1}{2} \mathrm{O}_2\)
- No energy is produced in this process but heat is liberated.
2. α-oxidation of fatty acids.
- Involves the removal of one carbon unit at a time.
- No binding of fatty acid occurs
- No energy is produced.
3. ω-oxidation of fatty acids.
- It involves hydroxylation followed by oxidation of o-carbon present as a methyl group.
- It requires cytochrome P450 NADPH, O2, and enzymes.
Functions of Cholesterol:
- It is a structural component of the cell membrane.
- Precursor for the synthesis of all other steroids in the body like vitamin D, bile acids, and steroid hormones.
- An essential ingredient in the structure of lipoproteins.
- Fatty acids are transported to the liver as cholesteryl esters for oxidation.
Question 4. What are ketone bodies? Describe their synthesis and utilization. (or) Briefly give the pathway of Ketogenesis. How is the presence of Ketone bodies in urine detected?
Answer:
Ketone bodies:
- Acetone, acetoacetate and (β-hydroxybutyrate are known as ketone bodies.
- They are water-soluble and energy-yielding.
Ketogenesis:
- Acetone, acetoacetate and (β-hydroxybutyrate are known as ketone bodies.
- They are water-soluble and energy-yielding.
Ketogenesis:
- It is the synthesis of ketone bodies.
- It occurs in the liver while the enzymes required for it are present in the mitochondrial matrix.
Reactions:
Acetyl CoA +Acetyl CoA
↓thiolase
Acetocetyl CoA
↓HMG CoA Iyase
Acetoacetate
↓
Spontaneous decarboxylation acetone
Reduction by dehydrogenase β-hydroxybutyrate
Utilization:
- Ketone bodies can be easily transported.
- Acetoacetate and (β-hydroxy butyrate serve as important energy sources for peripheral tissues
- Utilized in starvation and diabetes mellitus as there is glucose deficiency in these conditions.
- Ketone bodies meet 50 – 70% of the energy requirement by the brain.
Question 5. Ketosis.
Answer:
- When ketone bodies synthesis is more than its utilization, its concentration in the blood increases.
- This condition is called ketonemia.
- The excretion of ketone bodies in urine is called ketonuria.
- Ketonemia along with ketonuria is referred to as ketosis.
Features:
- The smell of acetone is a characteristic feature of ketosis.
- It is associated with starvation and severe uncontrolled diabetes mellitus.
1. Starvation:
2. Diabetes mellitus:
Question 6. Define lipoproteins. Classify lipoproteins and explain their function.
Answer:
Lipoproteins:
- Lipoproteins are molecular complexes consisting of lipids and proteins
Classification:
Functions:
- Lipids are hydrophobic in nature while proteins are hydrophilic
- Thus lipoproteins consisting of both hydrophobic and hydrophilic portion helps in the transport of lipids through the bloodstream
- Lipids get broken down into triglycerides in the body
- These triglycerides are transported from mucosal cells of the small intestine to the body cells
- Thus chylomicrons from the first stage of transport of lipids
- Lipids are also synthesized in the liver
- VLDL transports these lipids containing high content of triglycerides from the liver to body cells
- The remaining triglycerides from VLDL either return to the liver or are transformed into LDL
- LDL transports cholesterol from the liver to body cells
- Thus,
- VLDL contains high content of triglycerides
- LDL contains high content of cholesterol
- High VLDL increases the risk of coronary artery disease
Question 7. Phospholipids.
Answer: These are compound lipids containing phosphoric acid along with fatty acids, nitrogenous bases, and alcohol.
Types:
Structure:
Functions:
- Along with proteins forms a structural component of the membrane and regulates its permeability.
- Maintain conformation of the electron transport chain.
- Help in the absorption of fat from the intestine.
- Required for transport of lipids.
- Prevents the occurrence of fatty liver.
- Arachidonic acid which is libera led from phospholipids ads as a person loi Urn syllabus of eicosanoids.
- Help in cholesterol removal from the body by reversal of cholesterol transport.
- Act as surfactants.
- Involvement in signal transmission across membranes.
- Cephalin help in blood clotting.
Question 8. Polyunsaturated fatty acids.
Answer:
Definitions:
Fatty acids with 2 or more double bonds are collectively known as polyunsaturated fatty acids (PUFFA),
Examples:
- Linoleic acid – CH3(CH2)4CH – CHCH2CH = CH(CH2)7COOH
- Linolenic acid CH3CH2CH = CHCH2CH = CHCH2CH = CH(CH2)7COOH
- Arachidonic acid – CH3(CH2)4CH – CHCH2CH = CHCH2CH = CHCH2CH= CH (CH2)3COOH
Clinical importance:
- Reduces the plasma cholesterol level.
- Help in the transport of cholesterol and its excretion from the body.
Sources:
1. Oils rich in PUFA content.
- Cotton seed oil
- Soyabean oil
- Sunflower oil
- Fish oil
2. Oils poor in PUFA content.
- Ghee and coconut oil.
Question 9. Saturated and unsaturated fatty acids. (or) Unsaturated fatty acids
Answer:
Saturated fatty acids:
- Do not contain a double bond
Example:
- Acetic acid – CH3 – COOH
- Propionic acid – CH2 – CH2 – COOH
- Butyric acid – CH3 (CH2)2 – COOH
- Valeric acid-CH3(CH2)3-COOH
- They are reduced to a great extent by (3-oxidation.
- By it, it provides a good amount of energy.
Unsaturated fat acids:
- They contain one or more double bonds.
- They exhibit geometric isomerism depending on the orientation of the groups around the double bond.
- If the atoms/acyl groups are present on the same side of the double bond it is a Cis configuration.
- If the groups are present on the opposite side of the double bond – it is a trans configuration.
- Cis isomers are less stable.
- Commonly occurring isomers are Cis isomers
- The (β-oxidation of unsaturated fatty acids requires isomerizing and epimerase enzymes.
Types:
1. Monounsaturated fatty acids.
- Contains one double bond.
- Examples:
- Palmitoleic acid – CH3(CH2)5CH = CH(CH2)7COOH
- Oleic acid – CH3(CH2)7 CH = CH(CH2)7COOH
2. Polyunsaturated fatty acids.
- Contains two or more double bonds.
- Examples:
- Linoleic acid – CH3(CH2)4CH – CHCH2CH = CH(CH2)7COOH
- Linolenic acid CH3CH2CH = CHCH2CH = CHCH2CH = CH(CH2)7COOH
- Arachidonic acid – CH3(CH2)4CH – CHCH2CH = CHCH2CH = CHCH2CH
= CH (CH2)3COOH
Question 10. Lipoproteins.
Answer:
- They are molecular complexes consisting of lipids and proteins.
Functions:
Transport of lipids in blood plasma.
- Delivers lipid components to various tissues for utilization.
Structure:
- It consists of
1. Neutral lipid core containing.
- Triglycerol
- Cholesterol ester.
2. Surrounded by coat shell of
- Phospholipids
- Apoproteins
- Cholesterol.
Classification:
- Deffccls are of two types.
- Hyperlipoproteinemias.
- Hyperlipoproteinemia.
1. Hyperlipoproteinemias:
2. Hyperlipoproteinemia:
Question 11. Cholesterol.
Answer:
- It is found exclusively in animals and hence also called animal sterol
- It is amphipathic in nature since it possesses both hydrophilic and hydrophobic regions.
Values:
Total cholesterol -150-200 mg/dl -80
- LDL fraction – 150 mg/til
- I IDL fraction -30 – 60 mg/ill
- VLDL fraction -20 – 40 mg/dl
Question 12. Good and bad cholesterol.
Answer:
Good cholesterol:
- HDL cholesterol is referred to as good cholesterol as its high concentration counteracts atherogenesis.
- It can be considered a highly desirable lipoprotein.
- It is synthesized in the liver.
- It transports cholesterol from the liver to peripheral tissues.
Bad cholesterol:
- LDL cholesterol is considered as bad cholesterol due to its involvement in atherosclerosis.
- It can be considered as lethally dangerous lipoproteins.
- It is formed from very low-density lipoprotein.
- It helps in the transport of cholesterol from peripheral tissues to the liver.
Question 13. Degradation of cholesterol.
Answer:
- Cholesterol is converted to bile acids, excreted in feces.
- Serves as a precursor for the synthesis of.
- Steroid hormones.
- Vitamin D
- Fecal sterols – coprostanol and cholestanol.
1. Synthesis of bile acids:
- It takes place in the liver
- First cholesterol is dehydrogenase to 7-hydroxy-choIesterd by 7 a-hydroxylase.
- Following it, primary bile acids – cholic acid and chenodeoxycholic acid are formed.
- Cholic acid gets conjugated with glycine and taurine to form conjugated bile acids glycocholic acid and taurocholic acid.
- In the intestine, primary bile acids undergo deconjugation and dehydroxylation to form secondary bile acids namely deoxycholic aid and lithocholic acid.
Enterohepatic circulation:
Bile salts synthesize in the liver.
- This is called enterohepatic circulation.
2. Synthesis of steroid hormones.
3. Synthesis of vitamin D.
7-Dehydrocholesterol, intermediate in cholesterol synthesis.
↓
Cholecalciferol by ultraviolet rays.
Question 14. Name the Ketone bodies, how are they formed? Mention two causes of Ketosis. (or) Formation of ketone bodies/ketogenesis
Answer:
Ketone bodies:
- Acetone
- Acetoacetate
- β – hydroxybutyrate.
Formation of ketone bodies/ketogenesis:
2 moles of acetyl CoA
↓ Thiolase
Acetoacetyl CoA
↓ HMG CoA synthase
β-hydroxyl β -methyl glutaryl CoA [HMG CoA]
↓ HMG CoA lyase
Acetoacetate
↓
Spontaneous decarboxylation → Acetone
Reduction be dehydrogenase → β- hydroxybutyrate
Causes of Ketosis:
- Starvation
- Severe uncontrolled diabetes mellitus.
Question 15. Briefly give the pathway of Ketogenesis. How is the presence of Ketone bodies in urine detected?
Answer:
Urine Detection of Ketone Bodies:
- Ketone bodies are detected in urine by Rothera’s test.
- Nitroprusside in an alkaline medium reacts with the keto group of ketone bodies.
- Results in the formation of a purple ring.
- It detects acetone and acetoacetate in urine but not (3-hydroxybutyrate.
Question 16. Role of carnitine in beta-oxidation.
Answer:
- Carnitine helps in the transport of fatty acids from cytosol to the mitochondrial matrix.
- The Acyl group of acyl CoA is transferred to carnitine by carnitine acyltransferase I.
- The acyl-carnitine thus formed is transported to the mitochondrial matrix.
- Carnitine acyl transferase II converts acyl-carnitine to acyl CoA and carnitine is released.
- This carnitine returns to the cytosol for reuse.
Question 17. Fatty liver.
Answer:
Excessive accumulation of lipids especially triacylglycerols in the liver results in fatty liver.
Features:
- Occurrence of droplets of triacylglycerols in the entire cytoplasm of hepatic cells.
- Impairment in metabolic functions of the liver.
- Fibrotic changes in the liver.
- Cirrhosis of the liver.
Causes:
1. Increased synthesis of triacylglycerols.
- It occurs due to
- High mobilization of free fatty acids from adipose tissue and their influx into the liver.
- Diabetes mellitus
- Starvation
- Alcoholism
- High-fat diet.
2. Impaired synthesis of lipoproteins – This may be due to.
- Defect in phospholipid synthesis.
- Block in apoprotein formation.
- Failure in the formation/ secretion of lipoprotein.
- Certain chemicals like carbon tetrachloride.
- This inhibits protein synthesis.
- Decreases ATP availability.
- Deficiency of vitamin E.
3. Endocrine factors
- Certain hormones like ACTH, insulin, thyroid hormones, adrenocortiocoids promote fatty liver.
Question 18. Digestion and absorption of tirglycerols.
Answer:
- Triglycerols undergo stepwise enzymatic hydrolysis to finally liberate free fatty acids.
- Initially, pancreatic lipase cleaves treacly glycerols at positions 1 and 3.
- This result information of 2 – monoacylglycerol and free fatty acids.
- Triacylglycerol →2-monoacylgIycerol + free fatty acids.
- Next, lipid esterase acts on monoacylglycerol, cholesteryl esters, and vitamins,s, etc. to liberate free fatty acids.
- It requires the presence of bile acids.
Inhibition:
- Pancreatic lipase is inhibited by bile acids.
- This is overcome by colipase.
Abnormality:
1. Steatorrhea:
- It is a condition characterized by the loss of lipids in the feces.
- It may be due to:
- Defect in bile secretion.
- Defect in pancreatic juice secretion.
- Impairment in lipid absorption.
2. Cholesterol stones:
- Formed when the liver secretes bile supersaturated with respect to cholesterol.
Question 19. Absorption of fats:
Answer:
Theories:
1. Lipolytic theory by Verzar.
- According to it, fats are completely hydrolyzed to glycerol and free fatty acids.
- These are absorbed either as soaps or in association with bile salts.
2. Partition theory by Frazer.
- States that the digestion of triacylglycerols is partial.
- The partially digested triacylglycerols along with bile salts form emulsions.
3. Bergstrom’s theory
- More recent and comprehensive theory.
- Bile salts form mixed micelles with lipids.
- Micelles have a disk-like shape with lipids at the interior and bile salts at the periphery.
- It helps in the transport of lipids from the intestinal lumen to the membrane of the intestinal mucosal cells which is the site of lipid absorption.
- Absorption is almost complete for mono glycerol and free fatty acids but not for water-insoluble lipids.
Question 20. Explain ketonemia and ketonuria. Describe reactions of ketogenesis.
Answer:
Ketonemia:
- When the rate of synthesis of ketone bodies exceeds the rate of utilization, their concentration in the blood increases
- This condition is called ketonemia.
Ketonuria:
- The excretion of ketone bodies in urine is called ketonuria
- Kelonaemia and ketonuria together are referred to as ketosis
Reactions of ketogenesis:
Two moles of acetyl CoA
↓←Thiolase
Acetyl CoA
↓
Acetyl CoA + Acetyl CoA
↓ ← HMG CoA synthase
B hydroxyl p methyl glutaryl CoA (ITMG CoA)
↓← HMG CoA lyase
Cleavage of HMG CoA
↓
Acetoacetate + acetyl CoA
↓
Acetoacetate
- Undergoes decarboxylation to form acetone
- Reduces by dehydrogenase to form p hydroxybutyrate
- Thus, ketone bodies namely acetone, acetoacetate, and p hydroxybutyrate are formed.
Question 21. Name derivatives of cholesterol. Give biochemical importance of 3 derivatives.
Answer:
Derivatives of Cholesterol:
1. Bile acids
- Primary bile acids
- Cholic acid and chenodeoxycholic acid are primary bile acids
- In the intestine, these acids undergo deconjugation and dehydroxylation to form secondary bile acids
- Conjugated bile acids
- Conjugation with glycine and taurine forms conjugated bile acids – glycocholic add and taurocholic acid
- They function as a surfactant
- In bile, they exist as sodium and potassium salts called bile salts
2. Steroid hormones
- Glucocorticoids – cortisol
- Promotes gluconeogenesis
- Increases circulating free fatty acids
- Exhibits catabolic and anabolic effects on protein and nucleic acid metabolism
- Mineralocorticoids – aldosterone
- Regulate water and electrolyte balance
- Androgen, estrogens, progestrin
- Affects sexual development and function
3. Vitamin D
- 7-dehydrocholesterol is converted into cholecalciferol – vitamin D
- Required for growth and development of bones
Question 22. What are essential fatty acids? Name them.
Answer:
- The fatty acids that cannot be synthesized by the body should be supplied with essential fatty acids.
- They are:
- Linoleic acid
- Linolenic acid
- Arachidonic acid.
Question 23. Functions of lipids.
Answer:
- They are fuel reserves of the body as triacylglycerols.
- Form Constituents of membrane structure.
- Regulate membrane permeability.
- Precursor of fat-soluble vitamins.
- Acts as cellular metabolic regulators.
- Protects internal organs as an insulating medium.
- Give shape and smooth appearance to the body.
Question 24. What are lecithins? Mention their physiological importance.
Answer:
- Lecithins are the glycerophospholipids class of phospholipids.
- Present in the cell membrane.
- It is phosphatidic acid with choline as a base.
- Represent storage form of body’s choline.
Question 25. Cholesterol.
Answer:
- It is exclusively found in animals.
- Widely distributed in all cells.
Structure:
- C27H46 O.
- It has
- One hydroxyl group at Cg
- The double bond between C5 and C5.
- 8 carbon aliphatic side chain attached to
- Contains a total of 5 methyl groups.
Properties:
- Weakly amphiphilic.
- Yellowish crystalline solid.
- Microscopically appears notched-shaped.
- Insoluble in water.
- Soluble in organic solvents.
Question 26. Fatty liver.
Answer:
- Accumulation of excessive lipids in the liver results in fatty liver.
Features:
- The appearance of droplets of triacylglycerols in entire cytoplasm of hepatic cells.
- Impaired metabolic functions of the liver.
- Cirrhosis of the liver.
Causes:
- Increased synthesis of triacylglycerols.
- Impairment in lipoprotein synthesis.
Question 27. Name the ketone bodies and two conditions in which they are exerted, (or) What is ketosis? List two causes of ketosis.
Answer:
Ketone bodies:
- Acetone
- Acetoacetate
- β-hydroxybutyrate.
Ketosis:
- Increased concentration of ketone bodies in blood is called ketonemia while excretion of ketone bodies in urine is called ketonuria.
- Ketonemia along with ketonuria is called ketosis.
Causes of ketosis/conditions where ketone bodies are excreted:
- Starvation
- Severe uncontrolled diabetes mellitus.
Question 28. Beta oxidation of fatty acids.
Answer:
Definition:
- Beta oxidation may be defined as the oxidation of fatty acids on the [3-carbon atom.
Results:
- Removal of acetyl CoA.
Stages:
- Activation of fatty acids.
- Transport of fatty acids.
- β-oxidation proper.
Question 29. Derivatives of cholesterol and their importance.
Answer:
Question 30. Normal values of cholesterol.
Answer:
Question 31. Beta oxidation – pathway and energetic.
Answer:
Energetics:
- Palmitoyl CoA undergoes 7 cycles of p-oxidation to yield 8 acetyl CoA.
- Actyl CoA can enter citric acid cycle.
Question 32. In which form are fats stored in our body? Where is fat stored?
Answer:
Form of fat storage:
- Fat is stored as triacylglycerol as a fuel reserve.
Site:
- Fat depots are present in the cytoplasm, cell walls, specialized areas, and nervous tissues.
Question 33. Atherosclerosis.
Answer:
- It is a complex disease characterized by the thickening or hardening of arteries due to the accumulation of lipids.
- It is a progressive disorder that narrows and ultimately blocks the arteries.
Causes:
- Directly correlated to plasma cholesterol and LDL and inversely to HDL.
- Disorders like diabetes mellitus, hypothyroidism, and nephrotic syndrome.
- Factors like obesity, smoking, stress, etc.
Question 34. Saponification.
Answer:
The hydrolysis of triacylglycerols by alkali, to produce glycerol and soaps is known as saponification.
Triacylglycerol + 3NaOH →Glycerol + 3-R – CooNa (Soaps)
Question 35. Name lipotropic substance.
Answer:
- Choline
- Methionine
- Inositol
- Folic acid
- Vitamin B12.
- Glycine
- Serine.
Question 36. List two functions of phospholipids and give two examples of them.
Answer:
Functions:
- Along with proteins forms a structural component of the membrane and regulates its permeability
- Maintains conformation of electron transport chain B Helps in absorption of fats from the intestine and prevents the occurrence of fatty liver
- Helps in cholesterol removal from the body
Examples:
- Glycerophospholipids
-
- Phosphatidic acid
- Lecithins
- Cephalins
- Plasmalogens
- Sphingophospholipids
Question 37. Classify lipoproteins and describe the functions of any two.
Answer:
Question 38. Name the ketone bodies. Mention their clinical significance.
Answer:
Ketone bodies:
- Acetone
- Acetoacetate
- Beta-hydroxybutyrate
Significance:
- Ketone bodies are easily transported from the liver to various tissues
- Acetoacetate and beta-hydroxybutyrate serve as important sources of energy for the peripheral tissues
- During prolonged starvation, ketone bodies are the major fuel source for the brain and other parts of the CNS
Question 39. Rothera’s test.
Answer:
- Rothera test is used for detecting ketone bodies in urine
- Nitroprusside in an alkaline medium reacts with the keto group of ketone bodies
- Results in the formation of a purple ring.
- It detects acetone and acetoacetate in urine but not beta-hydroxybutyrate.
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