Lipids/fatty/sterols Flashcards
What are phospholipids composed of?
A glycerol backbone, two fatty acids, and a phosphate group, which may be linked to additional functional groups such as choline, ethanolamine, or serine.
What roles do phospholipids play in cellular function?
Structural: Integral components of cellular membranes, providing barrier properties. Signaling: Involved in cellular signaling cascades (e.g., phosphatidylinositol serves as a precursor for second messengers like IP3 and DAG).
How are phospholipids synthesized?
Step 1: Glycerol-3-phosphate reacts with two molecules of fatty acyl-CoA to form phosphatidic acid. Step 2: Phosphatidic acid is dephosphorylated to diacylglycerol. Step 3: Diacylglycerol reacts with head groups like CDP-choline to form specific phospholipids such as phosphatidylcholine.
What are the major types of phospholipids found in membranes?
Phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylinositol (PI).
What are sphingolipids, and how are they synthesized?
Sphingolipids are lipids with a sphingosine backbone. Synthesis begins with serine and palmitoyl-CoA to form sphinganine, which is modified to ceramide. Ceramide can be further converted into sphingomyelin or glycosphingolipids, depending on the attached head group.
What roles do sphingolipids play in health and disease?
Key functions in cell signaling and structural integrity of membranes. Dysregulation of sphingolipid metabolism is implicated in lysosomal storage diseases such as Niemann-Pick and Gaucher’s diseases.
What are sterols, and why are they essential?
Cholesterol, a primary sterol, stabilizes membrane fluidity and serves as a precursor for steroid hormones, bile acids, and vitamin D.
What are the precursors and cofactors required for fatty acid synthesis?
Precursors: Acetyl-CoA and malonyl-CoA. Cofactors: NADPH (reducing power), biotin (in acetyl-CoA carboxylase), and ATP.
What are the steps involved in fatty acid synthesis?
Step 1: Acetyl-CoA carboxylation to malonyl-CoA by acetyl-CoA carboxylase (rate-limiting step). Step 2: Fatty acid synthase complex elongates the fatty acid chain by adding 2-carbon units from malonyl-CoA.
How is fatty acid synthesis regulated?
Positively regulated by insulin and citrate. Inhibited by glucagon, epinephrine, and palmitoyl-CoA (feedback inhibition).
How are triacylglycerols (TAGs) synthesized?
Glycerol-3-phosphate serves as the backbone, which undergoes esterification with three fatty acids to form TAGs.
What is the significance of lipid synthesis in cells?
Essential for storing energy in adipose tissues. Provides structural components for membranes and signaling molecules.
What are the key steps in cholesterol synthesis?
Step 1: Acetyl-CoA forms HMG-CoA via thiolase and HMG-CoA synthase. Step 2: HMG-CoA is converted to mevalonate by HMG-CoA reductase (rate-limiting step). Step 3: Mevalonate is transformed into isoprene units, which polymerize to form squalene and eventually cholesterol.
What regulates cholesterol synthesis?
Feedback inhibition by cholesterol. HMG-CoA reductase activity is suppressed by statins and high sterol levels.
What are cholesterol derivatives?
Steroid hormones (e.g., cortisol, testosterone), bile salts, and vitamin D.
What is β-oxidation, and where does it occur?
The process of breaking down fatty acids to acetyl-CoA, occurring in the mitochondrial matrix.
What are the steps of β-oxidation?
Step 1: Fatty acids are activated to fatty acyl-CoA in the cytoplasm. Step 2: Transported into mitochondria via the carnitine shuttle. Step 3: Sequential dehydrogenation, hydration, oxidation, and cleavage to release acetyl-CoA.
What is the energy yield from β-oxidation?
Each cycle generates 1 NADH, 1 FADH2, and 1 acetyl-CoA, which enter the TCA cycle for further ATP production.
How is β-oxidation regulated?
Inhibited by malonyl-CoA, preventing simultaneous fatty acid synthesis and degradation.
