ansc314 - lipids

lipids

physical - compounds soluble in organic non-polar solvents, but insoluble in water

• ether, benzene, chloroform

chemical - ESTERS of fatty acids and glycerol (or some other alcohol), and waxes, terpenes, etc

lipid functions

• stored energy in body

• components in plasma membrane of all cells

• has vitamin A, D, E, K

• insulation & lubrication

lipid classifications

plant lipid functions

• structural - leaves 7% of DM

• surface lipids are waxes

• plasma membranes are mostly glycolipids (40-50%)

• storage in seeds - oils (simple lipids)

animal lipid functions

• store energy → 97% of adipose tissue (triglycerides)

• structural lipids → phospholipids

• blood plasma → free or non-esterified FA (NEFA), triglycerides (esterified)

• hormones & vitamins

simple lipids

• triacylglycerols

  • triglycerides

• di & monoglycerides - smaller quantities in nature

triacylglycerols

triglycerides

• most nutritionally significant of lipid groups esters of FA w/ alcohol (glycerol)

• tri - acyl esters of glycerol

  • form bulk of animal & plant fats & oils

tripalmitin

3 molecules of palmitic acids combine w/ one molecule of glycerol

• formation of triglyceride as simple lipid

butterfat

fatty acids

(FA) - determine the properties of fats

• classification:

  • saturated (no double bonds)

  • unsaturated (w/ double bonds)

animal FA

• even # carbon atoms (2-24)

• straight chain

• carboxyl group (-COOH) at end

  • odd chain but only from absorption of microbial derived FA

FA structure

all FA have 3 components

• carboxylic acid (alpha) end

• methyl (or omega) end

• fatty acid back bone

saturated FA

FA w/ no double bonds

volatile FA

• acetic

• propionic

• butyric

  • descending order → ↑ # carbon

unsaturated FA

FA that have double bonds

• mono-unsaturated

• poly-unsaturated

monounsaturated FA

only 1 double bond

• mono-enes

  • Oleic acid, 1 double bond (olive oil)

    • CH₃(CH₂)₇CH = CH(CH₂)₇COOH  (18:1 cis-9)

polyunsaturated FA

more than 1 double bond

• polyenes

  • Linoleic acid, two double bonds  (Di-ene)

    • CH₃(CH₂)₄CH = CHCH₂CH = CH(CH₂)₇COOH

      • (18:2 cis-9,12)

  • Linolenic acid, three double bonds (Tri-ene)

    • CH₃CH₂CH = CHCH₂CH = CHCH₂CH = CH(CH₂)₇COOH

      • (18:3 cis-9,12,15)

geometric isomerism

• cis configuration

• trans configuration

cis configuration

functional groups are on the same side of the C=C bond

• most FA are in cis configuration

trans configuration

functional groups on opposite sides of C=C bond

• formed by rumen bacteria & during processing of vegetable oils

• milk have small amts of trans fatty acids

oleic acid

naming unsaturated fatty acids

counting carbons:

• start from carbox. acid as 1st carbon → down chain

IUPAC Name

• 1st → cis or trans

• 2nd → positions of double bonds from carboxyl end

• 3rd: # of carbons

• 4th: # of double bonds

FA properties

• melting point

• degree of unsaturation

melting point

determined by:

• carbon chain length

  • ↑ chain length → ↑ MP

  • ↓ chain length → ↓ MP

    • < 10 C chain = liquid (oil) @ room temp

    • > 10 C chain = solid (fat) @ room temp

      • more DB

• ex

  • butyric acid (4C) - rumen VFA → MP -8 °C (liquid)

  • stearic acid (18C) - beef tallow → MP +70 °C (solid)

  • arachidic acid (20C) - margarine/peanut butter → MP +76 °C (solid)

degree of unsaturation

#C=C

• overrides chain length

• ↑ DB → ↓ MP

  • composition of triacylglycerol FA determine phys nature

  • high proportion of short chain & saturated FA have low MP

• ex

  • oleic acid (18:1) - palm & rapeseed oil → MP +13 °C (liquid)

  • 𝛼-linolenic acid (18:3) - linseed oil - MP -15 °C (liquid)

FA list

saturated vs unsaturated FA

• More saturated fat makes fat firmer, more solid.

• plants, marine oils (fish)

  • linoleic, linolenic, oleic (soft fats)

  • tropical oils (coconut, palm)

• mammals

  • palmitic, stearic acids - firm/hard fat

    • subcutaneous fat - high unsaturated (soft)

    • deep body fat (kidney) - saturated - firm/harder

• ruminants

  • fat deposit more saturated & fat firmer

  • hydrogenated in rumen

• monogastrics

  • tissue fat resembles fats in diet

• marine fishes

  • longer chain & PUFA - liquid soft

foods

story line: sperm whales

• 18,000kg of spermaceti oil in the head (mix of triacylglycerols and waxes with lots of unsaturated fatty acids

• Liquid at 37⁰C, begins to crystalize at lower temps at deeper levels of the ocean

• Buoyancy of the whale changes to match the density of the sea water while feeding, by the lipids crystalizing at lower temps.

• Endangered due to widespread hunting

elongation & ω-groups metabolic scheme

• only FA animal’s CAN”T make are linoleic & 𝛼-linolenic acid

  • linolenic (C 18:3)

• oleic made from steric w/ Δ9 desaturase past last 9 C from methyl end

elongation & ω-groups metabolic scheme

• linoleic can be desaturated → linolenic = gamma-linolenic (not essential)

  • omega-6 not omega-3 linolenic

• arachidonate made w/ acetate added → carboxyl end of linoleic

  • acetate always added/removed from carboxyl end

    • domestic cats can’t convert linoleic acid → arachidonate b/c don’t have Δ⁶ desaturase to perform conversion

• eicosapentanoic (EPA) made by desaturating 𝛼-linolenic & elongating to C20

  • DHA made by furthering desaturating EPA

    • steps are slow so EPA & DHA (fish oils) required in diet

desaturase

enzyme that removes 2 H atoms form fatty acid

• creates C=C DB

• Δ9 desaturase used to synthesize oleic acid, ubiquitous component of all cells in human body

essential FA

• linoleic & 𝛼-linolenic acid

  • must be obtained from diet

  • animals can’t introduce C=C between 9th C from methyl end

• arachidonic acid & γ-Linolenic synthesized from linoleic (ω-6)

  • cats can’t convert linoleic → arachidonic so need in diet

• Δ-6 desaturase & Δ-5 desaturase activity rate-limiting for synthesis of EPA & DHA for humans

  • ↑ amts omega 6 (corn oil) competes for enzyme w/ omega 3

polyunsaturated FA (PUFA)

3 PUFA classes

• linoleic family (ω-6) - growth, fertility, maintaining skin & RBC structure

• linolenic family (ω-3) - eye structure & function & central nervous system (CNS)

• oleic family (ω-9)

  • more double bonds, closer to omega end

• Animals can make omega-9 oleic family, but not omega 6 & omega 3

PUFA functions

• phospholipid - structural components - linoleic & arachidonic acids

• fat transport - deficiency characterized by fatty livers

• cholesterol transport - FA form lipoproteins, HDL, LDL, VLDL

  • deficiency ↓ HDL → ↑ VLDL & LDL

• precursor of eicosanoids

  • prostaglandins - blood pressure & clotting

  • thromboxane - platelet aggregation, vaso constrictors

  • prostacyclins - oppose actions of thromboxanes

• dietary FA balance (ω-3/ω-6) affects actions/activity of Eicosanoids (ω-3 more anti-inflammatory)

  • Corn oil has much more Ω-6 than Ω-3, therefore Americans get more Ω-6

essential FA deficiency