Govt Exams
In the fed state, high citrate levels allosterically activate ACC, and insulin signaling causes PKB/Akt to phosphorylate and activate ACC. This promotes fatty acid synthesis. Conversely, AMPK phosphorylation inactivates ACC during energy deprivation.
Sterol 27-hydroxylase catalyzes the side-chain oxidation of cholesterol to form bile acid precursors. Its deficiency or dysfunction leads to cholestanol accumulation and neuropathy. Elevated cholestanol is a characteristic finding in sterol 27-hydroxylase deficiency.
Linoleic acid (omega-6 PUFA) is essential because humans lack the enzyme delta-12 desaturase needed to introduce double bonds beyond carbon-9. Only plant-based sources provide linoleic and alpha-linolenic acids. Other fatty acids can be synthesized de novo.
The E4/E4 genotype carries the highest genetic risk for late-onset Alzheimer's disease. ApoE4 is less efficient at clearing amyloid-beta and is associated with increased neuroinflammation. E4 carriers show earlier cognitive decline compared to E2 and E3 carriers.
Niemann-Pick disease Type A is caused by deficiency of acid sphingomyelinase, leading to accumulation of sphingomyelin and cholesterol in lysosomes of various tissues, particularly the CNS, liver, and spleen. It presents with hepatosplenomegaly and neurological deterioration.
Palmitate (16 carbons) undergoes 7 cycles of beta-oxidation (n/2 - 1), each producing one acetyl-CoA. The final cycle releases 2 acetyl-CoA molecules, totaling 8 acetyl-CoA. Each 2-carbon unit is released as acetyl-CoA.
Familial hypercholesterolemia results from defective LDL receptors, leading to severely elevated LDL cholesterol (200-1000 mg/dL). This causes premature atherosclerosis, xanthomas, and corneal arcus. The defect prevents normal clearance of LDL from circulation.
Phospholipids have both hydrophilic (phosphate group) and hydrophobic (fatty acid chains) regions, making them amphipathic. This property allows them to spontaneously form bilayers in aqueous solutions, serving as the structural foundation of biological membranes.
Type III hyperlipoproteinemia results from apoE2 homozygosity combined with another genetic or environmental factor. ApoE2 has reduced affinity for lipoprotein receptors, impairing remnant particle clearance.
LCAT is synthesized primarily in the liver and, to a lesser extent, in other tissues. It plays a crucial role in HDL remodeling by converting free cholesterol to cholesterol esters.