How many desaturases do mammals have?
Click to see answer
Four desaturases.
Click to see question
How many desaturases do mammals have?
Four desaturases.
What are the initial apoproteins in chylomicrons?
Apo B48 and Apo A.
What are the two main enzymes involved in fatty acid synthesis?
Fatty acid synthase and Acetyl CoA carboxylase.
What is the final product of the cholesterol synthesis pathway?
Cholesterol.
What is the significance of condensation in lipid metabolism?
It is a key step in the synthesis of lipids from precursors.
What role do thioester derivatives play in lipid metabolism?
They are involved in the loading of precursors.
What inhibits Acetyl-CoA carboxylase?
Increased fatty acid concentrations.
What are the fates of cholesterol in the body?
Cholesterol ester, biliary cholesterol, bile acids, hormones, and vitamins.
During prolonged starvation, what percentage of the brain's energy requirements can ketone bodies provide?
About 70%.
What is the first stage of fatty acid synthesis?
Loading of precursors via thiol ester derivatives.
What happens to fatty acids in the capillaries of adipose tissue and muscle?
They are hydrolyzed by lipoprotein lipase and absorbed by the tissues.
What happens to VLDL as triglycerides are removed?
It is converted to IDL and then to LDL.
What is the function of acyl-CoA: cholesterol acyl transferase (ACAT)?
ACAT transfers fatty acids of CoA to the C3 hydroxyl group of cholesterol.
Where are bile acids synthesized and stored?
Synthesized in the liver and stored in the gallbladder.
What role does Apo C play in lipid metabolism?
Apo C transports exogenous fatty acids to adipose and skeletal muscle and activates lipoprotein lipase.
Where is Acetyl-CoA carboxylase located in mammals?
In the smooth endoplasmic reticulum (SER).
What are the three main types of ketone bodies produced in the liver?
Acetoacetate, β-hydroxybutyrate, and acetone.
What is the first step in cholesterol biosynthesis?
Conversion of Acetyl CoA to Mevalonate.
What does propionyl-CoA convert to for entry into the TCA cycle?
Succinyl-CoA.
What HDL level is associated with a lower risk of CHD?
HDL levels above 50 mg/dL.
What is the role of ApoA-I in HDL metabolism?
It is synthesized de novo in the liver and small intestine and helps form nascent HDL particles.
What are the key processes involved in lipid metabolism?
Reduction, dehydration, and condensation of precursors.
Which enzyme catalyzes the first committed step in cholesterol synthesis?
HMG-CoA reductase.
What is a precursor to bile salts and steroid hormones?
Cholesterol.
What is the precursor to cholesterol synthesis?
Acetyl coenzyme A.
Where are apolipoproteins synthesized?
In the small intestine.
What enzyme esterifies free cholesterol in HDL?
Lecithin:cholesterol acyl transferase (LCAT).
What are the fates of cholesterol?
Membranes, esters, biliary cholesterol, bile salts, hormones, and vitamins.
How do cells take up LDL?
Via LDLR-mediated endocytosis, which requires apo B-100.
What is the first and committed step of fatty acid synthesis?
Catalyzed by Acetyl-CoA carboxylase.
How is Acetyl-CoA carboxylase hormonally regulated?
Glucagon and epinephrine stimulate phosphorylation, leading to inactivation of the enzyme.
What is a limitation of mammals regarding fatty acid desaturation?
Mammals cannot incorporate a double bond beyond a certain point in the fatty acid chain.
What is the role of lipoprotein lipase in lipid metabolism?
It hydrolyzes triglycerides in VLDL and chylomicrons.
What is produced from the final round of beta-oxidation of odd-chain fatty acids?
Propionyl-CoA.
What hormones are involved in the fasted state that promote fatty acid oxidation?
Epinephrine and glucagon.
What is formed after the cyclization of unsaturated carbons in the cholesterol synthesis pathway?
Lanosterol.
What is the primary site for regulating cholesterol synthesis?
HMG-CoA reductase.
What does Lovastatin resemble in structure?
Mevalonate.
What is the normal level of ketone bodies in blood?
1 mg/mL.
Which apolipoproteins are acquired in the small intestine?
Apo B48 and Apo A.
What is the relationship between HDL levels and coronary heart disease (CHD)?
Higher HDL levels correlate with reduced risk of atherosclerosis and CHD.
What enzyme adds oxygen to squalene to form an epoxide?
Squalene monooxygenase.
What is one of the primary functions of cholesterol?
It stabilizes cell membranes.
What is the fate of chylomicron remnants?
They are taken up by the liver, requiring Apo E for recognition.
What is the structural characteristic of cholesterol?
It has a cyclopentanophenanthrene structure consisting of four fused rings.
What is produced from Mevalonate in cholesterol biosynthesis?
2 Activated Isoprenes.
What is the rate-limiting step of cholesterol synthesis?
The conversion of HMG-CoA to mevalonate.
Where does beta-oxidation primarily occur?
In the mitochondrial matrix.
What is required for the transport of fatty acids to mitochondria?
A carrier.
What is the role of biotin in fatty acid synthesis?
It is a cofactor that is dependent for the activity of Acetyl-CoA carboxylase.
What type of drugs inhibit HMG-CoA reductase to lower cholesterol?
Statin drugs (e.g., Lovastatin).
What is cholesterol a precursor for?
Synthesis of all other steroids.
How does HDL acquire cholesterol from peripheral tissues?
By acquiring it from macrophages in tissue subendothelial spaces.
What pathway provides NADPH for fatty acid synthesis?
Pentose phosphate pathway.
What is the primary function of LDL in the body?
To serve as primary plasma carriers of cholesterol for delivery to all tissues.
What is the major function of HDL?
Reverse cholesterol transport, transporting peripheral tissue cholesterol back to the liver.
What coenzymes and cofactors are required for fatty acid synthesis?
Biotin, NADPH, Mg++, Mn++.
What processes are involved in the third stage of fatty acid synthesis?
Reduction, dehydration, and reduction.
What is the primary function of VLDL?
To transport endogenously derived triglycerides to extra-hepatic tissues.
What is the primary component of chylomicrons?
Dietary triglycerides (over 80%).
What role do bile acids and salts play in digestion?
They act as effective detergents aiding in the absorption of lipids, cholesterol, and fat-soluble vitamins.
How are chylomicrons secreted into the body?
They are secreted into lymphatics rather than directly into the bloodstream.
What is the major form of energy derived from dietary lipids?
Triacylglycerol (TAG).
What happens to TAG during fasting?
Fatty acid oxidation is favored as fats serve as fuel.
What enzyme hydrolyzes TAG to free fatty acids and glycerol?
Hormone-sensitive lipase.
What are the optimal LDL cholesterol levels?
Less than 100 mg/dL.
What happens to glycerol after being released from chylomicrons and VLDL?
It is taken up by the liver and kidney and converted into a glycolytic intermediate.
How do chylomicrons enter circulation?
Via the left subclavian vein.
What is the primary fate of acetyl-CoA from β-oxidation?
Most enters the Krebs cycle, but some form ketone bodies.
What functional groups are present in cholesterol's structure?
A hydroxyl group at C3, a double bond between C5 and C6, and methyl groups at C10 and C13.
What is the role of ATP-binding cassette protein G1 (ABCG1) in HDL metabolism?
It facilitates the transfer of cholesterol.
What regulates HMG-CoA reductase?
Feedback, degradation, and modification.
What effect does prenatal androgen exposure have on females with CAH?
It has a masculinizing effect on the development of external genitalia.
What is the genetic defect associated with familial hypercholesterolemia?
A mutation in the LDL receptor gene.
What occurs in the second stage of fatty acid synthesis?
Condensation of precursors.
How is cholesterol obtained?
Through diet or synthesis.
What are the main types of lipoproteins involved in lipid transport?
Chylomicrons, VLDL, LDL, and HDL.
Where is excess cholesterol stored?
As cholesterol esters in cytosolic lipid droplets.
What is the typical composition of lipoproteins?
Triglycerides and cholesterol esters internally, phospholipids externally.
What is the primary function of HDL?
Reverse cholesterol transport.
What percentage of LDL uptake occurs in the liver?
75%.
What disease is associated with cholesterol metabolism?
Atherosclerotic vascular disease.
Where is cholesterol primarily synthesized in the body?
Mostly in the liver and intestine.
What condition can excessive amounts of ketone bodies cause?
Ketoacidosis.
What happens to chylomicron remnants after metabolism?
They are taken up by the liver.
Which apolipoprotein is exclusively associated with LDL?
Apo B-100.
What are some functions of HDL beyond cholesterol transport?
Anti-inflammatory, antioxidant, and vasodilatory effects.
What apoproteins are required for IDL to interact with hepatic receptors?
Both Apo B-100 and Apo E.
What protein interacts with HDL during cholesterol binding?
ATP-binding cassette transport protein A1 (ABCA1).
What hormone increases during the fed state and inhibits hydrolysis of stored triglycerides?
Insulin.
What effect do trans-fatty acids have on HDL and LDL levels?
They lower HDL and increase LDL.
What type of fatty acids are most naturally occurring?
Even-numbered fatty acids.
What role does lipoprotein lipase play in lipid metabolism?
It acts on adipose and muscle capillaries to process lipoproteins.
What are the relative sizes of lipoproteins from largest to smallest?
Chylomicrons, VLDL, LDL, HDL.
What is the goal of correcting the deficiency in cortisol secretion in CAH?
To suppress ACTH overproduction.
What are the three stages of fatty acid oxidation?
Activation of fatty acids, transport into mitochondria, and β-oxidation in the mitochondrial matrix.
What is the most common enzyme deficiency in congenital adrenal hyperplasia (CAH)?
21-hydroxylase deficiency.
What happens to endocytosed LDL in lysosomes?
Apoproteins are degraded and cholesteryl esters (CE) are hydrolyzed to yield free cholesterol.
