Lecture 7-Structures of Lipids Flashcards
Lipids:
• Soluble in organic solvents
○ i.e. ether, chloroform, acetone
• Wide variety of structures and functions
• Source of energy
Major component of cell and organelle membranes
Lipid Functions:
• Concentration source of energy
○ 9kcal/g
• Palatability of foods and increase satiety
• Source of essential fatty acids
○ Alpha-linolenic acid (omega-3), linoleic acid (omega-6)
• Carrier of fat-soluble vitamins
○ A,D,E, and K
• Necessary for growth and development
• Important precursors for the production of hormones
• Effect inflammation and blood clotting
• Key roles in disease development
Atherosclerosis, diabetes, obesity…etc
Fatty Acids:
• Saturated ○ Consists of only single bonds (max number of H atoms) • Unsaturated ○ One or more double bonds § Mono/polyunsaturated ○ Can be in cis or trans configuration Missing H atoms
Fatty Acid Nomenclature:
• Delta system
○ Numbering starts from carboxyl end of fatty acid
• Omega system
○ Numbering starts from methyl end of fatty acid
Will never have double bonds closer than 3 carbons (first double bond wil be at carbon 3 or later
Example
Discovery of Essential Fatty Acids:
• Rats fed diets that were completely fat free
○ Resulted in stunted growth, lost fur, inflamed and scaly tails
• Infants fed diets that differed in fat content
Diets with less than 0.1% linoleic acid has poor growth and thickened, dry skin
Essential Fatty Acids (EFA):
- Humans lack the enzymes necessary to insert double bonds beyond the delta-9 position of a fatty acid
- Delta-12 and delta-15 fatty acids are found in plants
- Omega 6 fatty acids make up 2-3% of diet
- Omega 3 fatty acids make up 1% of energy in diet
Diagram
Essential Fatty Acid Deficiency:
• Need both omega 3 and omega 6 fatty acids to be healthy
• Deficiencies are rare in humans (don’t need very much of each)
Infants, and hospitalized patients more susceptible to deficiency
Chart
Changes in Fatty Acid Consumption Over Time:
• Consumption of total fat, trans, omega fat has increased over time
• Omega 6 comes from corn, corn is found in many sources
In the future, trans fat with go down to 0
Companion Animals and EFA Deficiency:
• Dogs and cats don’t have the enzymes required to convert essential fatty acids into the fatty acids that the body needs (needs supplementation)
• Deficiency results in impaired reproductive efficiency, wound healing, dry coat, scaly skin
• Rare in pets unless they eat low fat dry foods
• Dogs need DHA supplementation
○ Can convert ALA to EPA, but not to DHA (need DHA supplementation)
• Cats needs EPA
Can’t convert ALA to EPA or DHA, so needs EPA and DHA
EFA Desaturation and Elongation:
• Enzymes increase the chain length and number of double bonds of essential omega 3 or omega 6 fatty acids
• Desaturases add double bonds
• Elongases increase chain length 2 at a time
• When consuming same amounts of omega 3 and omega 6, arachidonic acid (AA) produced will be equal to eicosapentaenoic acid (EPA), inflammatory response is balanced
When omega 6 is more prevalent in diet, more AA is produced, causes an imbalance in the inflammatory response
Diagram + Explanation
Eicosanoid Production:
• Fatty acids rarely found as free fatty acids in the body- buildup would lead to lipotoxicity, usually found as triglycerides or phospholipids
• Eicosanoids are generated using fatty acids in phospholipids (2 fatty acids and a polar head group)
• Of the 2 fatty acids, one is a polyunsaturated (PUFA) omega 3 or omega 6 fatty acid
• Enzyme (PLA2-Phospholipase A2) cleaves off arachadonic acid, freeing it from the phospholipid (can not be converted into an eicosanoid)
• Arachadonic acid can enter several different pathways, generating different structures with different functions
○ Cyclooxygenase pathway mediated by COX enzyme
○ Epoxidase pathway mediated by Cyp450 enzyme
Lipoxygenase pathways mediated by LOX enzyme
Diagram
Eicasonoid Regulation:
• Over the counter drugs can be used to regulate these enzymes
○ Corticosteroids are often found in asthma treatments, lowers the number of eicosanoid available, results in less inflammatory signalling
○ Turning off enzymes to produce eicosanoids decreases pro-inflammatory precursors
• Omega 6 to omega 3 ratio in lipids is usually 20:1, consuming more omega 6 (found in fish) brings it more to a 1:1 ratio
Results in one phospholipid with omega 3, one with omega 6, inflammation signaling becomes more regulated
Triglycerides (TAGs):
• Main dietary lipid
• Major storage lipid
• Important for lipogenesis, lipolysis, transport in lipoproteins
○ End product of lipogenesis (liver produces lipids and repackages them as triglycerides and sends them off to the body)
○ Lipolysis breaks down TAGs, releasing energy potential
○ TAGs packaged in lipoproteins (transport carriers for fats)
• Structures
○ Monoacylglycerol (MG, MAG)
○ Diacylglycerol (DG, DAG)
○ Triacylglycerol/Triglyceride (TD, TAG)
• Triglycerides can’t be absorbed, needs to be simplified to a monoglyceride (one fatty acid), which can then be transported and absorbed
Diglycerides have 2 fatty acids attached to the glycerol backbones, plays signalling role in body (i.e. insulin signalling)
Phospholipids (PL):
- More polar than TAGs (have a hydrophilic phosphate head)
- Component of membranes
- Source of physiologically active fatty acids for eicosanoid synthesis
- Anchors membrane proteins
- Intracellular signalling
Sterols:
• Steroid alcohol (monohydroxy alcohols)
• Can be free, or esterfied with a fatty acid (cholesterol ester)
• Cholesterol found from diet- meat and eggs (40%), produced endogenously (60%)
• Essential component for membranes
• Precursor for
○ Bile acid production
○ Steroid sex hormone production
○ Vitamin D synthesis
If body is making too much cholesterol, easy fix is to lower dietary cholesterol
