Lipids 1: Lipids Properties and Classes Flashcards
Biological functions of lipids
- energy source and storage
- major component of cell membranes
- insulation
- precursors to hormones and eicosanoids
- Others: biological detergent, membrane anchors for proteins, receptors
How do lipids serve as barriers?
Not water soluble but the rest of the body is aqueous hence like a barrier
Chemical classification of lipids
- fatty acids
- glycerolipids
- glycerophospholipids
- steroids
- eicosanoids
- wax
- sphingolipids
Another term for FFAs
Free fatty acids → non-esterified fatty acids
Structure of FFAs
- Head: carboxylic acid
- Tail: hydrocarbon chain
How are most FFAs bound in plasma?
99% of FFAs are bound to albumin
* high plasma [FFA] are found locally in adipose tissue during fat catabolism
How are fatty acids classified?
- By chain length
- By degree of saturation
What are the classifications of chain length for fatty acids?
- short chain: ≤ 6 carbons
- medium chain: 8-14 carbons
- long chain: >14 carbons
What are the classifications for degrees of unsaturation?
- saturated: no double bonds and every carbon is sp3 hybridized
- unsaturated: 1 or more double bonds
- monosaturated: 1 double bond therefore 2 adjacent carbons are sp2 hybridized
- polyunsaturated: more than 1 double bond therefor more than 2 carbons are sp2 hybridized
What is the most common FA in the diet?
Palmitic Acid/ Hexadecanoic acic
What is the structure of palmitic acid?
- chain length = 16 carbons
- An acid end and a methyl end
- C16H32O2
- 16:0
What degrees of saturation can there be?
0, 1, 2, 3 double bonds
* saturated: all carbons bonded with H, so can compact together making them more stable and solid at room temperature
* Unsaturated: contains double bonds therefore less H atoms causing a kink such that they cannot stack easily are typically liquid at room temperature
What are the two types of nomenclature for fatty acids?
- Miller notation
- Omega notation
Describe the Miller notation nomenclature for fatty acids
- 18:2n-6
- 18= number of carbons in the
whole molecule
2= number of db bonds
-6= subtract this value from n to derive the carbon atom where the last double bond starts (18-6=12), count from the carboxyl end
Describe the Omega notation nomenclature for fatty acids
- 18:2ω6
- 18= number of carbons in the whole molecule
- 2= number of db bonds
- ω=label for the last acyl carbon
- 6 = the carbon number for the first double bond from the methyl end
Common Saturated fatty acids
- Myristic acid 14:0
- Palmitic acid 16:0
- Stearic acid 18:0
- Arachidic acid 20:0
- Lignoceric acid 24:0
Common unsaturated fatty acids
- Palmitoleic acid 16:1∆9 (n-7)
- Oleic acid 18:1∆9 (n-9)
- Linoleic acid 18:2∆9,12 (n-6)
- 𝝰-linolenic acid 18:3∆9,12,15 (n-3)
- Arachidonic acid 20:4∆5,8,11,14 (n-6)
- Eicosapentaenoic acid 20:4∆5,8,11,14,17 (n-3)
- Docohexaenoic acid 22:6∆4,7,10,13,16,19 (n-3)
Common short chain fatty acids (SCFAs)
- Acetic acid 2:0
- Propionic acid 3:0
- Butyric acid 4:0 (butter)
Common medium chain fatty acids (MCFAs)
- Caproic acid 6:0 (butter)
- Caprylic acid 8:0
- Lauric acid 12:0 (coconut & palm oils)
What is the notation for cis- and trans- unsaturated fatty acids?
- cis- is implied
- trans- is placed before the C#
How are polyunsaturated fatty acids with trans- notated?
c or cis, t or trans can be used in the name
* 18:2ct, 18:2tt or 18:2tc for isomers with 18 carbons and 2 double bonds
How are most trans found?
Mostly formed by industrial hydrogenation or by biohydrogenation in the stomachs of ruminant animals
* i.e. isomers of conjugated linoleic acid: c9,t11-CLA and t10,c12-CLA
How are most cis found?
Cis FAs more abundantly found in nature, therefore in the body as well
What is the effecy of TFA in the diet?
increased TFA diet will result in increased TFA in body fat stores and membranes
* Negative effect on health bi increasing CVD risk (↑LDL and ↓HDL)
* Adipose can be a biomarker of TFA intake
What about natural TFAs?
Some TFAs are naturally occuring such as those in cows and sheep milk and may have a positive effect on health
* still reccomended to reduce to less than 1%
What is the idea behind hydrogenation of fatty acids?
essentially to convert the more unsaturated (plant) fatty acids to saturated by adding in hydrogen and decreasing double bonds. This was initially thought to be a potential healthier alternative to saturated fats.
What was the effect og hydrogenation of fatty acids?
- changed functional properties such as melting point and mouth feel
- bi-product was TFAs from partial hydrogenation so the cis arrangement changed to trans
Sources of saturated fatty acids
keep in mind mixture of FAs
Sources of TFAs
keep in mind mixture of FAs
Structures of common fatty acids
* palmitic acid
* eliadic acid
* oleic acid
* linoleic acid
* arachidonic acid
* linolenic acid
* docosohexaenoic acid
What are glycerolipids?
Main form of fat storage
What are the types of glycerolipids?
- MAG
- DAG
- TAG
What is the most common glycerolipid in the body?
TAG
* SN1 and SN3 could be either SFA or USFA
* SN2 is usually an unsaturated fatty acid to keep fat in the body in the liquid phase otherwise our fat would be like butter
Structure of TAG
- glycerol backbone made up of 3 carbons SN1, SN2, SN3 with FAs linked via ester bond (alcohol + acid)
- SN1 and SN3 are usually on the right and SN2 are usually on the left
- SN2 is typically an USFA
- Overall the fatty acids attached to the glycerol can be combination of SFAs, MUFAs, and PUFAs
What is the reaction which links the FAs to the glycerol to form glycerolipids?
condensation reaction
* glycerol+3 fatty acids=tryglyceride+3H2O
* SN2 mainly unsaturated
Simple vs. complex TG
- simple: 3 FAs are the same
- complex: 3 FAs are different
What uses TAG as major lipid storage?
plants and higher animals
Where else might fat be stored besides the adipose tissue?
yellow bone marrow
* made mostly of fat and contains stem cells that can become cartilage, fat, or bone cells.
Properties of TG FAs
- firmess
- stability
- oxidation of FAs
How does firmness change between different TG FAs?
Generally: ↓ chain length or ↑ double bond results in ↑fluidity
* liquid at room temperature
How does stability change between different TG FAs?
↓ chain length or ↑ double bonds results in ↓ stability
* more readily oxidized
What FAs are most susceptible to oxidation?
PUFA
What is the result of FA oxidation?
- off/rancid/’warmed-over’ flavours and odours in the food
What is used to prevent FA oxidation in foods?
tocopherols and butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT)
* preserve colour and flavour by preventing oxidation
General dietary fat composition of
* animal fats
* tropical oils
* vegetable oils
What are glycerophospholipids?
The main structural building blocks of cell membranes
* polar head group is hydrophillic and faces out
Structure of phospholipids
- glycerol backbone
- FAs in positions sn-1 and sn-2
- phosphate group in position sn-3
How are glycerophospholipids classified?
classified according to head group
* phosphatidyl choline
* phosphatidyl ethanolamine
* phosphatidyl serine
* phosphatidyl inositol
* phosphatidyl glycerol
What is the most common phospholipid?
phosphotidyl choline
* ~60%
Functions of phospholipids (PPLs)
physiological
* cell membrane structure
* intracellular messengers
food industry
* emulsifiers: lecithin from egg yold, wheat germ, soy bean
How is cholesterol present in the body?
- free cholesterol
- cholesterol esters
Where are cholesterol esters typically found in the body?
in plasma cholesterol is esterified at the 3’OH group for storage and transport
* often arachidonic acid
What is cholesterol a aprt of when plasma cholesterol levels are measured?
the cholesterol in part of the lipoproteins so either LDL or HDL
Role of cholesterol in the body
Modulating membrane compressibility, permeability, fusibility, thickness and organization
Where does dietary cholesterol come from?
animal source foods only
What cholesterol do plants have?
phytosterols
What cholesterol do plants have?
phytosterols
What is cholesterol the precursor for?
- parent compound for steroid hormones and are stored as precursors
- precursor for bile acids
- precursor for fat soluble vitamins (A, E, D, K)
What are thr 5 major classes of steroid hormones?
- androgens
- estrogens
- progestins
- mineralcorticoids
- glucocorticoids
What are the classes of phytosterols?
- β-sitosterol
- campersterol
- stigmasterol
Role of bile acids
- solubilize phospholipids and cholesterol (detergents)
- Aid in digestion and absorption of fat and fat-soluble vitamins in the intestine
What do bile acids conjugate with to be secreted as bile?
conjugate with taurine or glycine in the liver in the final step before being secreted
* Conjugation substantially reduces the passive reabsorption of the molecule through biological membranes.
What can bile acid deficiency lead to?
- fat malabsorption
- malnutrition
- gall-stones
- celiac disease
- ileal resection
