Lipids Flashcards
(15 cards)
What are the main functions of lipids?
- energy storage in the highly reduced fatty acids: have high potential for oxidation and hence releasing lots of energy; store 2x more energy than carbohydrates
- insulation: heat and shock absorption, also triglycerides
- water repellent in swimming birds and sheep; waxes
- cuticle in leaves to prevent water evaporation in plants, also waxes
- building blocks for cell membranes (compartmentalisation to generate electrochemical gradient and allow only necessary substances to pass); phospholipids; anchoring for memrane proteins.
- light absorbing pigments
- some vitamins are lipids
- steroid hormones
What are the key properties of lipids?
- all substances which are water insoluble (hydrophobic)
- very diverse hence have different physical and chemical properties
- oils are viscous liquids
- fats are soft and greasy
- wax is hard
What is the typical structure of a fatty acid?
- head slightly hydrophilic (polar) group: anionic carboxylic group with pKa 4.5-5
- hydrophobic hydrocarbon chain, over 100 types according to length (4-36 carbons; predominantly even numbers due to the way they are synthesized from Acetyl CoA) and saturation (number and location of double bonds and stereoisomers)
- unsaturated can be ether cis or trans configuration; cis is more common
- cis (example: oleic acid) is bent (has a kink); hence cannot be closely packed and are usually liquids and have low melting temperature
- trans (example: elaidic acid) is a straight chain; hence packs well and are usually solids and have high melting temperature
- the longer chain, the higher melting point and lower solubility
- the more double bonds, the lower melting point
What are the features of fatty acid nomenclature?
- first carbon is from carboxylic group, often labeled as alpha
- the lowest carbon is omega
- one double bond is monounsaturated
- more double bonds is polyunsaturated
- 18:0 means there is 18 carbons and no double bonds (stearic acid)
- 18:1 delta 9 means there is 18 carbons and one double bond at position 9 (alternatively, it can be called omega 9 if counted from the bottom) (oleic acid)
- 18:2 delta 9,12 means there is 18 carbons and 2 double bonds at positions 9 and 12 (alternatively, omega 6,9) (linoleic acid)
- 18:3 delta 9,12,15 means there are 18 carbons and 3 double bonds at positions 9, 12 and 15 (alternatively, omega 3,6,9) (linolenic acid)
What are the fatty acid compositions of olive oil, butter and beef fat?
Olive oil:
- 80% C16-18 unsaturated (with double bonds)
- 15% C16-18 saturated
- 5% C4-14 saturated (no double bonds)
Butter:
- 40% C16-18 unsaturated
- 40% C16-18 saturated
- 20% C4-14 saturated
Beef fat:
- 50% C16-18 saturated
- 45% C16-18 unsaturated
- 5% C4-14 saturated
Why trans fats are unhealthy and how they are formed?
Unsatursted Cis fats are often hydrogenated to saturated fats to prevent oxidation and increase shelf life. However, trans fats appear as a side product of this process.
Trans fats increase risk for cardiovascular disease.
What are the 2 key categories of lipids?
1) neutral storage lipids - triglycerides (glycerol + 3 fatty acids, each linked with ester bonds to glycerol)
- simple triglycerides: 3 same fatty acids
- but most of them have 3 different fatty acids
- present as large fat droplets in adipose tissue
- lipase decomposes triglycerides to free fatty acids
2) polar amphipatic membrane lipids: phospholipids (glycerophospholipids/phosphoglycerides and sphingolipids), glycolipids and sterols (cholesterol and its derivatives);
- glycerophospholipids: glycerol + two fatty acids (one saturated and another unsaturated; can be any, very diverse) + phosphodiester link with phosphate (anion) and charged/highly polar head group (choline, serine etc);
- sphingolipids: no glycerol but end appears similar to it; sphingosine (long aliphatic chain amino alcohol) + fatty acid attached to sphinosine through amide bond + head group substituent (just H in ceramide)
What is the function of sphingolipids?
If carbohydrade head group (glucose; globoside/lactosylceramide with 2-4 monosaccharides; ganglioside with complex branched oligosaccharides), than cellular recognition: support proteins laying on plasma membrane.
If sphingomyelin with phosphocholine, than present in myelin sheath of neuron.
What is a typical example of gangliosides?
Structures which determine ABO blood group types.
O - no antigen present, just glucose, galactose, N-acetylglucosamine, galactose, fucose
A - same but also N-acetylgalactosamine
B - same but also galactose
What are the features of sterols?
- cholesterol derivatives
- steroid nucleus: 4 fused rings (3 with 6Cs, 1 with 5Cs)
- polar head group (hydroxyl), derivatives can have more
- alkyl side chain in cholesterol, absent in most derivatives
- control fluidity of membranes
- steroid hormones and intracellular messagers (plants also send volatale lipids for communication)
- pigments for photosynthesis and vision
What are the examples of steroid hormones?
- testosterone
- estradiol
- cortisol
- aldosterone
- brassinolide (growth hormone in plants)
Synthetic anti-inflammatory drugs: prednisone
Which vitamins are fat soluble?
A, D, E, K
Which vitamins are precursors of steroids?
A and D
D regulates Ca2+ uptake in bone, liver and intestines
Which membrane lipids are most common?
Glycerophospholipids
What are the properties of waxes?
Long fatty acid chains with long chain alcohols (about 30 carbons), 80-100 degrees melting point.
