Lipids Flashcards
characteristics of lipids
- soluble in organic solvents (e.g ether, chloroform, acetone)
- wide variety of structures and functions
- source of energy
- major component of cell and organelle membranes
lipid functions (8)
- concentrated energy source (9kcal/g)
- palatability of food and increase satiety
- source of essential fatty acids (omega-3 and 6)
- source of fat-soluble vitamins (A, D, E and K)
- necessary for growth and development
- important precursors for production of hormones
- affect inflammation and blood clotting
- key roles in disease development (atherosclerosis, diabetes, obesity, etc)
saturated fatty acids
- maximum number of hydrogens
- only single bonds
- butyric acid: in the stomach - from bacteria
- palmitic acid: most common that we eat
monounsaturated fatty acid
- missing hydrogens
- only one double bond
- oleic acid: 18:1 cis-configuration
- elaidic acid: 18:1 trans-configuration
polyunsaturated fatty acid
- missing hydrogens
- multiple double bonds
- the more double bonds, the more kinked the structure, the more fluid the membrane
omega system nomenclature
- numbering starts from the methyl (CH3) end
e.g. 18:2 n-6 OR w-6
18 = number of carbons
2 = number of double bonds
6 = location of 1st double bond
delta system nomenclature
- numbering starts from the carboxyl end (COOH)
- e.g. 18:2 delta^9,12
18 = number of carbons
2 = number of double bonds
9,12 = position of double bonds
essential fatty acid discovery
Barr experiment: fed rats diets that were completely fat-free and noticed stunted growth, lost fur, inflamed and scaly tails
- Infant experiment: fed infants diets with <0.1% linoleic acid and noticed poor growth and thickened dry skin
what are the essential fatty acids?
linoleic acid (18:2 n-6) aka. omega-6
alpha linoleic acid (18:3 n-3) aka. omega-3
- humans lack the enzymes necessary to insert DBs beyond the delta-9 position of a fatty acid therefore we have to get from food we consume (abundant in plants)
- the delta-12 and 15 FAs are produced in plants
signs of omega-6 deficiency
skin: dermatitis (water leaves the membrane, leads to lost moisture and potential infection)
growth: decreases
reproductive maturity: decreases
CNS and retinal development are OK
signs of omega-3 deficiency
skin, growth and reproduction are OK
CNS development: IQ decreases
Retinal development: visual acuity decreases
who is most susceptible to EFA deficiency
infants: formula isn’t properly designed
hospitalized patients: fluid diets don’t contain proper amounts of EFAs
how much EFAs in our diet do we need to avoid deficiency?
omega-6 = 2-3% of energy in diet
omega-3 = 1% of energy in diet
why can an imbalance of omega3 and 6 cause problems
n-6 is used to make pro-inflammatory molecules
n-3 is used to make anti-inflammatory molecules
what makes pets susceptible to EFA deficiency?
Dogs: can convert ALA to EPA but not DHA which they require in their diet
Cats: lack the enzymes to make LCFA which they require in their diet
EFA desaturation and elongation
- converts ALA and LA to downstream metabolites (humans are not good at this)
- desaturation removes hydrogen (creates DB)
- elongation adds 2 carbons
how does linoleic acid (18:2 n-6) lead to pro-inflammatory eicosanoid production?
- linoleic acid -> gamma-linoleic acid (via delta-6 desaturase)
- -> dihomo-gamma-linoleic acid (via elongase 5)
- -> arachidonic acid (via delta-5 desaturase)
how does alpha-linoleic acid (18:3 n-3) lead to anti-inflammatory eicosanoid production?
- a-linoleic acid -> stearidonic acid (via delta-6 desaturase)
- -> eicosatetraenoic acid (via elongase-5)
- eicosapentaenoic acid (via delta-5 desaturase)
- EPA can be further converted to DHA if needed
linoleic acid metabolism
- new double bond added at 6th position of carbon backbone from carboxyl end
- two carbons added (from malonyl CoA) at carboxyl end
- new double bond added at 5th position from carboxyl end
*always do modifications from carboxyl end
what are eicosanoids?
- metabolites of 20-carbon FAs (mostly derived from AAs and EPAs)
- have rapid degradation - act where they were made
- produced by most cells
- hormone-like function, but act locally (don’t travel)
- role in inflammation, platelet aggregation, blood pressure, etc.
- common ones: PGD2, TXA2, LTE4
how do we produce eicosanoids?
- start with a phospholipid
- phospholipase A2 removes the omega-6 chain to give arachidonic acid (PLA2 can be inhibited by corticosteroids)
- 1 of 3 pathways happens from here…
1. cyclooxygenase pathway: uses COX enzyme, can be inhibited by aspirin
2. Epoxidase pathway: uses CYP540 enzymes
3. Lipoxygenase pathway: uses LOX enzyme
What are triglycerides (TAGs)?
- major dietary and storage lipid
- critical in lipogenesis, lipolysis and are transported in lipoproteins
- contains a glycerol backbone + 3 fatty acid tails ( connected by ester bonds
- can have mono, di, or triacylglycerol structures
- fatty acid composition determines physicochemical properties