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Aulani "Biokimia" Presentation 6
Lipid Biochemistry
Aulanni’amBiochemistry LaboratoryChemistry DepartmentBrawijaya University
Aulani "Biokimia" Presentation 6
Lipids: Hydrophobic molecules
Fats (animal) and Oils (plant) - energy storage, insulation
– Fatty acid - Long hydrocarbon tail with carboxly -COOH group at the head.
• Saturated - no double bonds; saturated with H
• Unsaturated - one or more H replaced by double bond - stays liquid
– Carboxyl groups on fatty acid link to -OH group on a 3-carbon alcohol (glycerol)
Aulani "Biokimia" Presentation 6
Source of stored energy in living organisms Lipids contain the elements carbon,
hydrogen, and oxygen Glycerol and fatty acids are the building
blocks of lipids Examples of lipids are fats and oils
fatty acid glycerol
Aulani "Biokimia" Presentation 6
For simplicity, the fatty acids will be abbreviated as:
glycerol + 3 fatty acids = a fat or oil
+ =
makes a fatty acid and 3 water molecules, 3 H2O
Since a fat or oil contains 3 fatty acid units, they are sometimes called triglycerides
HOOC-R
where "R" simply represents the long carbon chain.
Aulani "Biokimia" Presentation 6
Phospholipids
One fatty acid replaced by phosphate PO4-
Molecule has Hydrophilic head, and long hydrophobic tail.
Fatty acids unsaturated- remains fluid Main component of cell membranes
Aulani "Biokimia" Presentation 6
Most Common Fatty Acids in Di- and Triglycerides
Fatty acid Carbon:Double bonds Double bonds
Myristic 14:0
Palmitic 16:0
Palmitoleic 16:1 Cis-9
Stearic 18:0
Oleic 18:1 Cis-9
Linoleic 18:2 Cis-9,12
Linolenic 18:3 Cis-9,12,15
Arachidonic 20:4 Cis-5,8,11,14
Eicosapentaenoic 20:5 Cis-5,8,11,14,17
Docosahexaenoic 22:6 Cis-4,7,10,13,16,19
CH3(CH2)nCOOH
Aulani "Biokimia" Presentation 6
We use fat in the form of triglyceride (3 fatty acids and 1 glycerol).
Aulani "Biokimia" Presentation 6
Fat Metabolism
Mostly handled by the liverFats must first be broken down to form
acetic acid which is subsequently oxidized.Oxidation (breakdown) of fats is not always
complete. Intermediate products accumulate in the blood causing the blood to become acidic (acidosis or ketosis)
Aulani "Biokimia" Presentation 6
Cholesterol
Structural basis of steroid hormones and vitamin D
Major building block plasma membranes15% of cholesterol comes from diet the
rest is made by the liver.Cholesterol is lost by breakdown, secretion
in bile salt and finally defecation
Aulani "Biokimia" Presentation 6
Lipoproteins
Fatty acids, fats, and cholesterol are insoluble in water and therefore are transported bound to small lipid-protein complexes called lipoproteins
Low-density lipoproteins (LDL) – transport cholesterol and other lipids to body cells
High-density lipoproteins (HDL) – transport cholesterol from tissue cells to liver for disposal
Ratio of HDL/LDL is important
Aulani "Biokimia" Presentation 6
Body Energy Balance
When energy intake and energy outflow are balanced – body weight remains stable
When they are not, weight is either lost or gained
Control of food intake: ?–Rising and falling blood levels of nutrients–Hormones–Body temperature–Psychological factors
Aulani "Biokimia" Presentation 6
Basal Metabolic Rate
The amount of heat produced by the body per unit of time under basal conditions
An average 155lb adult has a BMR of about 60-72 kcal/hour
Aulani "Biokimia" Presentation 6
Lipids
Catabolism Aerobic
transport of fatty acids from cytosol to mitochondria (role of carnitine)
-oxidation in mitochondria 4 steps
release of NADH and FADH2
108 ATP/palmitic acid or 7 ATP/Carbon
Aulani "Biokimia" Presentation 6
Catabolism: dietary lipids Digestion:
a) Slow relative to carbohydrates b) In small intestine with action of
bile salts c) FAcs absorbed across intestinal
wall and reconverted to TAGsd) Transported as chylomicrons
Mobilisation from adipocytes: a) FAcs transported in blood bound to
serum albumin; dissociates in cells oxidation
b) glycerol undergoes glycolysis
Role of glucose 6-phosphatase in maintaining blood glucose levels (in the liver, not the muscles)
Aulani "Biokimia" Presentation 6
Synthesis: lipogenesis
carried out by two cytosolic enzymes, acetyl-CoA carboxylase and fatty acid synthase
Requires: NADPH, ATP and biotin, CO2
Sources of Acetyl CoA - transfer of citrate from mitoch. to
cytosol NADPH - malic enzyme in cytosol
- pentose phosphate pathway
Aulani "Biokimia" Presentation 6
Lipid Digestion - Rumen
DigalDigly MonogalDigly
Galactose
Propionate Diglyceride
Glycerol
Triglyeride Fatty acids
Saturated FA CaFA Ca++ Feed particles
-galactosidase
-galactosidase
Lipase Anaerovibrio lipolytica
H+
Reductases
Lipase
Aulani "Biokimia" Presentation 6
Fat Digestion
Digestibility influenced by:Dry matter intake
Decreases with greater intakeAmount of fat consumed
Digestibility decreases 2.2% for each 100 g of FA intake (Response is variable)
Degree of saturationDigestibility decreases with increased saturationMaximal digestion with fats having Iodine values greater than 40
Aulani "Biokimia" Presentation 6
1. Minimal degradation of long-chain fatty acids in the rumen
Fatty acids not a source of energy to microbes2. Active hydrogenation of unsaturated fatty acids3. Microbial synthesis of long-chain fatty acids in the rumen (15g/kg nonfat org matter fermented)4. No absorption of long chain fatty acids from the rumen
More fat leaves the rumen than consumed by the animal
Lipids leaving the rumen• 80 to 90% free fatty acids attached to feed particles and microbes• ~10% microbial phospholipids leave the rumen• Small quantity of undigested fats in feed residue
Lipid Metabolism - In the Rumen
Aulani "Biokimia" Presentation 6
• Synthesize C 18:0 and C 16:0 in 2:1 ratio using acetate and glucose (straight-chain even carbon #).• If propionate or valerate used, straight-chain odd carbon fatty acids synthesized.• Branched-chain VFA used to produce branched chain fatty acids.• About 15 to 20% of microbial fatty acids are mono- unsaturated. No polyunsaturated fatty acids are synthesized.• Some incorporation of C 18:2 into microbial lipids.
Microbial Fatty Acid Synthesis
Aulani "Biokimia" Presentation 6
Hydrogenation of Fatty Acids in the Rumen
Polyunsaturated fatty acids (all cis)Isomerase (from bacteria) Needs free carboxyl group
and diene double bond
Shift of one double bond (cis & trans)
Hydrogenation Hydrases (from bacteria,
Hydrogenated fatty acid mostly cellulolytic)
(stearic and palmitate)
Aulani "Biokimia" Presentation 6
Hydrogenation of Fatty Acids in the Rumen
All unsaturated fatty acids can be hydrogenated
Monounsaturated less than polyunsaturated
65 to 96% hydrogenationNumerous isomers are producedBiohydrogenation is greater when high foragediets fedLinoleic acid depresses hydrogenation of FA
Aulani "Biokimia" Presentation 6
Conjugated Linoleic Acid - RumenMost Common Pathway (High Roughage)
Linoleic acid (cis-9, cis-12-18:2)
Conjugated linoleic acid (CLA, cis-9, trans-11-18:2)
Vaccenic acid (Trans-11-18:1)
Stearic acid (18:0)
Cis-9, trans-12 isomerase Butyrivibrio fibrosolvens
Aulani "Biokimia" Presentation 6
CLA Isomers - Rumen (High Concentrate) Low Rumen pH
Linoleic acid (cis-9, cis-12-18:2) Cis-9, trans-10 isomerase
CLA Isomer (trans-10, Cis-12-18:2)
This isomer is inhibitory to milk fat synthesis.
Trans-10-18:1
Aulani "Biokimia" Presentation 6
Linolenic Acid – Oleic Acid
Linolenic acid (cis-9, cis-12, cis-15-18:3)
(Cis-9, trans-11, cis-15-18:3)
Trans-11, cis-15-18:2
Trans-11-18:1 (vaccenic acid)
Oleic acid cis-9 (18:1) Stearic acid (18:0)
Aulani "Biokimia" Presentation 6
CLA absorbed from the intestines available for incorporation into tissue triglycerides.
Reactions from linoleic acid to vaccinic acid occur at a faster rate than from vaccinic acid to stearic acid.
Therefore, vaccinic acid accumulates in the rumen and passes into intestines where it is absorbed.
Quantities of vaccinic acid leaving the rumen several fold greater than CLA.
Aulani "Biokimia" Presentation 6
Conversion of Vaccinic Acid to CLA In mammary gland and adipose
Trans-11-18:1 CLA, cis-9, trans-11 18:2
Stearoyl CoA Desaturase‘9-desaturase’
This reaction probably major source of CLA inmilk and tissues from ruminants.
Also transformsPalmitic PalmitoleicStearic Oleic
Aulani "Biokimia" Presentation 6
Synthesis: lipogenesis
carried out by two cytosolic enzymes, acetyl-CoA carboxylase and fatty acid synthase
Requires: NADPH, ATP and biotin, CO2
Sources of Acetyl CoA - transfer of citrate from mitoch. to
cytosol NADPH - malic enzyme in cytosol
- pentose phosphate pathway
Aulani "Biokimia" Presentation 6
Synthesis: lipogenesis
Other roles of PPP alternative pathway for glucose
metabolism production of ribose 5-phosphate
(nucleotide synthesis)
Ketone bodies arise from the overflow pathway in liver; major source of energy for heart, muscle and brain (fasting and diabetes)
Location of lipid metabolism oxidation in mitoch., synthesis in cytosol
Aulani "Biokimia" Presentation 6
Summary of fatty acid metabolism in the Summary of fatty acid metabolism in the
liverliver
Aulani "Biokimia" Presentation 6
If excess fat is consumed, there is no mechanism by which the body can increase its use of fat as a fuel.
Instead, when excess fat calories are consumed, the only option is to accumulate the excess fat as an energy store in the body, and this process occurs at a low metabolic cost and is an extremely efficient process.