Đề thi, bài tập trắc nghiệm online Hóa sinh lipid – Đề 3

Waxes are esters of long-chain fatty acids and long-chain alcohols. Their hydrophobic nature makes them excellent protective coatings to prevent water loss in plants (leaves, fruits) and provide waterproofing in animal skin and feathers. They are not primarily for energy storage or membrane structure.

Bile salts are amphipathic molecules synthesized in the liver and secreted into the small intestine. Their primary role is to emulsify large fat globules into smaller droplets, increasing the surface area for lipases (enzymes that hydrolyze triacylglycerols) to act effectively.

Phospholipids are amphipathic lipids with a hydrophilic head and hydrophobic tails, making them ideal for forming the lipid bilayer structure of cell membranes. Triacylglycerols are for energy storage, steroids have signaling and structural roles, and fatty acids are building blocks or fuel sources.

Lipids primarily function in energy storage, membrane structure, and signaling. Catalysis of biochemical reactions is the primary function of enzymes, which are typically proteins, not lipids.

Cholesterol is a steroid lipid that serves as the precursor molecule for all steroid hormones, including hormones like cortisol, testosterone, and estrogen. Palmitic acid is a fatty acid, glycerol is a component of triglycerides and phospholipids, and sphingosine is a component of sphingolipids.

The defining difference is the presence of carbon-carbon double bonds. Saturated fatty acids have no double bonds, leading to a straight chain, while unsaturated fatty acids have one or more double bonds, causing bends in the chain. This affects their packing and physical properties.

Gaucher disease is caused by a deficiency in glucocerebrosidase, an enzyme that breaks down glucocerebroside. As a result, glucocerebroside accumulates in lysosomes, particularly in macrophages, leading to various symptoms.

Ketoacidosis is a metabolic state associated with pathologically elevated levels of ketone bodies, typically in uncontrolled diabetes mellitus. It leads to a decrease in blood pH (acidosis) and can be life-threatening.

Sphingolipids are a class of lipids built from sphingosine, an amino alcohol, and fatty acids. Unlike glycerophospholipids which are based on glycerol, sphingolipids have a sphingosine backbone. They are important components of cell membranes, particularly in nerve tissue.

The complete oxidation of palmitic acid yields approximately 106 ATP molecules. This high energy yield is due to the extensive beta-oxidation cycles and the subsequent entry of acetyl-CoA into the citric acid cycle and oxidative phosphorylation.

LDL is often referred to as 'bad cholesterol′ because it carries cholesterol from the liver to peripheral tissues. High levels of LDL can contribute to cholesterol buildup in arteries. HDL ('good cholesterol′) performs the reverse function, transporting cholesterol back to the liver.

Sphingomyelin is a type of sphingolipid that is a major component of the myelin sheath, a protective and insulating layer around nerve fibers. This sheath is crucial for rapid nerve impulse transmission.

Phospholipase A2 (PLA2) is an enzyme that specifically hydrolyzes the ester bond at the sn-2 position of phospholipids, releasing fatty acids like arachidonic acid. Arachidonic acid is a precursor for eicosanoids, including prostaglandins and leukotrienes, which are involved in inflammation and signaling.

Acetyl-CoA is the two-carbon unit that is sequentially added to a growing fatty acid chain during fatty acid biosynthesis. This process primarily occurs in the cytoplasm and is catalyzed by fatty acid synthase.

Arachidonic acid, a 20-carbon polyunsaturated fatty acid with four double bonds, is the primary precursor for most eicosanoids in humans. Eicosanoids include prostaglandins, thromboxanes, leukotrienes, and lipoxins, all derived from arachidonic acid through enzymatic pathways.

Carnitine acts as a carrier molecule to transport long-chain fatty acyl-CoA from the cytoplasm across the inner mitochondrial membrane into the mitochondrial matrix, where beta-oxidation occurs. This transport system is essential for the utilization of long-chain fatty acids as fuel.

Acetoacetate, beta-hydroxybutyrate, and acetone are the three main ketone bodies. Pyruvate is a product of glycolysis and is involved in carbohydrate metabolism, not ketogenesis.

Ketogenesis is upregulated during prolonged fasting, starvation, or in uncontrolled diabetes when glucose availability is limited. In these conditions, the body shifts to using fatty acids as a primary fuel source, leading to increased beta-oxidation and the production of ketone bodies in the liver.

Retinal is a derivative of Vitamin A (retinol), which is a lipid-soluble vitamin. Retinal is a crucial component of rhodopsin, the light-sensitive pigment in rod cells of the retina, essential for visual signal transduction (converting light into nerve signals).

Acetyl-CoA carboxylase (ACC) catalyzes the carboxylation of acetyl-CoA to malonyl-CoA, which is the committed step in fatty acid biosynthesis. ACC activity is regulated by various factors, including citrate (activator) and palmitoyl-CoA (inhibitor).

HDL is known for its role in reverse cholesterol transport. It picks up excess cholesterol from peripheral tissues and returns it to the liver for excretion or conversion to bile acids. This process is considered protective against atherosclerosis.

HMG-CoA reductase is the key regulatory enzyme in cholesterol biosynthesis. Statin drugs are competitive inhibitors of HMG-CoA reductase, effectively reducing cholesterol production in the liver and thus lowering blood cholesterol levels.

Lipid rafts are specialized microdomains within cell membranes that are enriched in cholesterol and sphingolipids. This composition makes them more ordered and less fluid compared to the surrounding phospholipid-rich membrane. Lipid rafts are involved in various cellular processes, including signal transduction and membrane trafficking.

The liver is the primary organ responsible for ketogenesis. Hepatocytes in the liver mitochondria produce ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone) from acetyl-CoA derived from fatty acid oxidation.

Prostaglandins are eicosanoids, a class of lipid derivatives derived from arachidonic acid. They act as local hormones and play crucial roles in inflammation, pain, fever, and blood clotting. Aspirin and ibuprofen inhibit prostaglandin synthesis.

Lipases are enzymes specifically designed to hydrolyze lipids, particularly triacylglycerols, breaking them down into fatty acids and monoacylglycerols. Amylase digests carbohydrates, protease digests proteins, and nuclease digests nucleic acids.

Chylomicrons are large lipoprotein particles synthesized in intestinal cells. They are responsible for transporting dietary triacylglycerols, cholesterol, and other lipids from the intestine to the lymphatic system and then to the bloodstream for delivery to tissues.

Essential fatty acids are those that cannot be synthesized by the human body and must be obtained from dietary sources. Linoleic acid (an omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid) are two essential fatty acids. Palmitic and stearic acids are saturated fatty acids, and oleic acid is a monounsaturated omega-9 fatty acid, all of which can be synthesized by the body.

Trans-fatty acids are associated with negative health impacts, particularly on cardiovascular health. They raise LDL ('bad′) cholesterol levels and lower HDL ('good′) cholesterol levels, contributing to an increased risk of heart disease. They are often found in processed foods and partially hydrogenated oils.

Beta-oxidation, the process of breaking down fatty acids to generate energy, takes place in the mitochondria of eukaryotic cells. This compartmentalization is crucial for energy production and regulation of metabolic pathways.