The structural difference that determines fat's physical state
Saturated: all single C-C bonds, no kinks, pack tightly โ solid at room temp (butter). Unsaturated: C=C double bonds โ kinks โ can't pack โ liquid (olive oil). Trans fats: artificially hydrogenated, behave like saturated.
Cell Membrane Structure
Phospholipid bilayer: hydrophilic heads face water, hydrophobic tails face inward
Cell Membrane Structure
The self-organizing phospholipid bilayer
Each phospholipid: polar head (faces water) + two nonpolar fatty acid tails (face inward). Bilayers form spontaneously. Fluid mosaic model: proteins float in this bilayer.
Cholesterol in Membranes
Cholesterol stabilizes membrane fluidity โ not too fluid, not too rigid
Cholesterol in Membranes
Cholesterol is the membrane's fluidity buffer
At high temperatures: restrains phospholipid movement โ prevents excess fluidity. At low temperatures: prevents tight packing โ prevents solidifying. A Goldilocks molecule.
Why steroid hormones work differently from peptide hormones
Steroids are derived from cholesterol. Lipid-soluble โ diffuse through membrane โ bind intracellular receptors โ directly regulate gene expression. Peptide hormones (insulin, glucagon) can't cross โ bind surface receptors.
Beta-Oxidation
Beta-oxidation: fatty acids broken into 2-carbon acetyl-CoA units in mitochondria โ ATP
Beta-Oxidation
How fatty acids are broken down to produce energy
Fatty acids are activated to acyl-CoA โ enter mitochondria โ each cycle removes 2 carbons as acetyl-CoA + produces FADHโ + NADH. Acetyl-CoA enters Krebs cycle. Fat produces more ATP per gram than carbohydrates.
Glycerophospholipid Structure
Glycerophospholipids: glycerol + 2 fatty acids + phosphate + head group. The main membrane lipid.
Glycerophospholipid Structure
The dominant structural lipid in cell membranes
Glycerol backbone: position 1 and 2 โ fatty acids (ester bonds). Position 3 โ phosphate + head group (choline โ phosphatidylcholine, serine โ phosphatidylserine, ethanolamine, inositol). Head group determines charge and interactions. Phosphatidylserine: negatively charged, faces cytoplasm, flips to outer leaflet during apoptosis.
Lipid signaling molecules derived from arachidonic acid
Arachidonic acid (20-carbon PUFA) released from membrane phospholipids by phospholipase Aโ. COX pathway: prostaglandins (inflammation, fever, pain) and thromboxanes (platelet aggregation, vasoconstriction). Lipoxygenase pathway: leukotrienes (bronchoconstriction, allergic response). Aspirin inhibits COX โ reduces prostaglandins โ anti-inflammatory.
Lipoproteins
Lipoproteins: transport lipids in blood. VLDL โ IDL โ LDL (bad cholesterol). HDL (good) takes cholesterol to liver.
Lipoproteins
How the body transports fats through the bloodstream
Lipoproteins: lipid + protein transport particles. VLDL: liver exports triglycerides. IDL: intermediate product. LDL: delivers cholesterol to tissues โ 'bad' because excess deposits in arterial walls. HDL: reverse cholesterol transport โ removes cholesterol from tissues back to liver โ 'good.' Apolipoproteins determine receptor binding.
VLDL
Liver exports triglycerides
LDL
Delivers cholesterol โ 'bad'
HDL
Removes cholesterol โ 'good'
Omega Fatty Acids
Omega-3 fatty acids: double bond at 3rd carbon from methyl end. Anti-inflammatory. EPA and DHA in fish oil.
Omega Fatty Acids
Naming convention and health significance of omega fatty acids
Omega (ฯ) position: carbon counting from the methyl end (omega end). Omega-3: double bond at 3rd carbon โ EPA and DHA (fish oil, anti-inflammatory, cardiovascular protection). Omega-6: double bond at 6th carbon โ linoleic acid (pro-inflammatory in excess). Omega-9: oleic acid in olive oil (monounsaturated, neutral).
Waxes
Waxes: fatty acid ester of long-chain alcohol. Waterproofing in plants (cuticle), animals (earwax, fur).
Waxes
Simple lipids with waterproofing and protective functions
Wax: ester of long-chain fatty acid + long-chain alcohol. Very hydrophobic โ excellent waterproofing. Plant cuticle wax: prevents water loss from leaves. Animal uses: earwax (cerumen), bee wax (honeycomb), spermaceti (whale), lanolin (sheep wool โ water resistance). Hard solid at room temperature.