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Lipids, membrane lipids, Storage lipids, 4DDD2606-0C89-4089-8C88…

- - - - decreases as the chain length increases
    - - decreases as the chain length decreases
      - decreases as the number of double bonds increases
  - - - Humans need them but cannot synthesize them.
      - They including ALA, DHA, and EPA.
        • although DHA and EPA can be synthesized from ALA
    - - common name: oleic acid
      - delta numbering of carbon skeleton: 18:1Δ9
        • describes location of the first carbon of the alkene in
        relationship to the carbonyl carbon
      - systematic name: cis-9-octadecanoic acid
      - omega numbering of carbon skeleton: 18:1ω9
        • describes location of the first carbon of the alkene in
        relationship to the terminal methyl
  - - - done to increase shelf life or stability at high temperature of oils used in cooking (especially deep frying)
    - - Avoid deep frying partially hydrogenated vegetable oils.
      - Current trend: reduce trans fats in foods (Wendy’s, KFC).
  - - - Almost all natural fatty acids have an even number of carbons.
      - Most natural fatty acids are unbranched.
- - - - high heat capacity (can “absorb” heat)
      - mechanical protection (can absorb shocks)
      - low thermal conductivity
    - - hydrophobic nature: keeps surface of the organism dry
        • prevents excessive wetting (birds)
        • prevents loss of water via evaporation
    - - reduced compounds: lots of available energy
      - hydrophobic nature: good packing
    - - increased density while diving deep helps sinking (just a hypothesis)
      - spermaceti organ may focus sound energy: sound stun gun?
  - - - steroid hormones (act body-wide)
      - growth factors
      - paracrine hormones (act locally)
      - vitamins A and D (hormone precursors)
    - - color of tomatoes, carrots, pumpkins, some birds
    - - vitamin K: blood clot formation
      - coenzyme Q: ATP synthesis in mitochondria
    - - vitamin E
    - - main structure of cell membranes
- - - - Liquid ones are called oils.
      - The primary storage form of lipids (body fat)
      - The majority of fatty acids in biological systems are
        found in the form of triacylglycerols.
      - Less soluble in water than fatty acids due to the
        esterification of the carboxylate group
      - Solid ones are called fats.
      - Less dense than water: fats and oils float.
    - - Fatty acids carry less water per gram because they are nonpolar.
      - Glucose and glycogen are for short-term energy needs and quick delivery.
      - Fatty acids carry more energy per carbon because they are more reduced.
      - Fats are for long-term (months) energy needs, good
        storage, and slow delivery.
    - - Insoluble and have high melting points
      - Variety of functions:
        
        waterproofing of feathers in birds
        
        protection from evaporation in tropical plants and ivy
        
        protection and pliability for hair and skin in vertebrates
        
        used by people in lotions, ointments, and polishes
        
        storage of metabolic fuel in plankton
      - Waxes are esters of long-chain saturated and unsaturated fatty acids with long-chain alcohols.
      - Ex: Beeswax is a mixture of a large number of lipids, including esters of triacontanol, and a long-chain alkane hentiacontane.
  - - - Different organisms have different membrane lipid head group compositions.
      - Different tissues have different membrane lipid head group compositions.
      - The properties of head groups determine the surface properties of membranes.
      - Diversification can come from:
        
        modifying a different backbone
        
        changing the fatty acids
        
        modifying the head groups
      - Contain polar head groups and nonpolar tails (usually attached fatty acids)
    - - Two fatty acids form ester linkages with the first and second hydroxyl groups of L-glycerol-3-phosphate.
      - The phosphate group is charged at physiological pH.
      - Primary constituents of cell membranes
      - General Structure of Glycerophospholipids
        
        Unsaturated fatty acids are commonly found connected to C2 of glycerol-3-phosphate.
        
        The highly polar phosphate group may be further esterified by an
        alcohol; such substituent groups are called the head groups.
      - Ex：Phosphatidylcholine
        
        Phosphatidylcholine is the major component of most eukaryotic cell membranes.
        
        Many prokaryotes, including E. coli, cannot synthesize this lipid; their membranes do not contain phosphatidylcholine
    - - Plasmalogen
        
        Common in vertebrate heart tissue
        
        Also found in some protozoa and anaerobic bacteria
        
        Vinyl ether analog of phosphatidylethanolamine
        
        Function is not well understood
        
        resistant to cleavage by common lipases but cleaved by few specific lipases
        
        Increase membrane rigidity
        
        Sources of signaling lipids
        
        May be antioxidant
      - Platelets-Activating Factor
        
        Aliphatic ether analog of phosphatidylcholine
        
        Acetic acid has esterified position C2
        
        First signaling lipid to be identified
        
        Stimulates aggregation of blood platelets
        
        Plays role in mediation of inflammation
    - - A fatty acid is joined to sphingosine via an amide linkage, rather than an ester linkage as usually seen in lipids.
      - A polar head group is connected to sphingosine by a
        glycosidic or phosphodiester linkage.
      - The backbone of sphingolipids is a long-chain amino
        alcohol sphingosine.
      - The sugar-containing glycosphingolipids are found
        largely in the outer face of plasma membranes.
      - The backbone of sphingolipids is NOT glycerol.
    - - Ceramide (sphingosine + amide-linked fatty acid) + phosphocholine attached to the alcohol
      - Sphingomyelin is abundant in myelin sheath that surrounds some nerve cells in animals.
    - - The blood groups are determined in part by the type of sugars located on the head groups in glycosphingolipids
      - The structure of sugar is determined by an expression
        of specific glycosyltransferases.
        
        Individuals with no active glycosyltransferase will have the O antigen.
        
        Individuals with a glycosyltransferase that transfers an
        N-acetylgalactosamine group have A blood group.
        
        Individuals with a glycosyltransferase that transfers a galactose group have B blood group.
    - - Phospholipids are degraded by phospholipases A−D.
        • Each phospholipase cleaves a specific bond.
      - Gangliosides are degraded via a series of enzymatic cleavages
        • Failure to correctly degrade gangliosides results in build-up of lipids in lysosomes, a dysfunction categorized as “lysosomal storage disorders.”
      - Most cells continually degrade and replace their membrane lipids
- - - - Mammals obtain cholesterol from food or synthesize it de novo in the liver.
      - Cholesterol, bound to proteins, is transported to tissues via blood vessels.
        – Cholesterol in low-density lipoproteins tends to deposit
        and clog arteries.
      - Cholesterol and related sterols are present in the membranes of most eukaryotic cells.
        
        thicken the plasma membrane
        
        modulate fluidity and permeability
        
        no sterols in most bacteria
      - Many hormones are derivatives of sterols.
    - - hydroxyl group (polar head) in the A-ring
      - various nonpolar side chains
      - steroid nucleus: four fused rings
    - - They are more polar than cholesterol.
      - Steroid hormones are synthesized from cholesterol in gonads and adrenal glands.
      - Steroids have the sterol nucleus but lack the alkyl chain found in cholesterol.
      - They are carried through the body in the bloodstream, usually attached to carrier proteins.
      - Steroids are oxidized derivatives of sterols.
      - Many of the steroid hormones are male and female sex hormones.
  - - - • prostaglandins (inflammation and fever)
      - • thromboxanes (formation of blood clots)
      - • leukotrienes (smooth muscle contraction in lungs)
    - - Involved in visual pigment
      - Precursor for other hormones involved in signaling
    - - Polyketides are a diverse family of compounds synthesized similarly to fatty acid biosynthesis.
      - commonly secondary metabolites with specialized function