aulani "biokimia" presentation 6 lipid biochemistry aulanni’am biochemistry laboratory...

Aulani "Biokimia" Presentation 6

Lipid Biochemistry

Aulanni’amBiochemistry LaboratoryChemistry DepartmentBrawijaya University


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)


A fatty acid


Building a fat molecule


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


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.


Saturated and unsaturated fats


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


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


Linolenic AcidOmega-3


Cell membrane- Phospholipid bilayer


Predominant Energy Pathways


We use fat in the form of triglyceride (3 fatty acids and 1 glycerol).


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)


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


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


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


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


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


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)


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


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


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


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


• 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 monounsaturated. No polyunsaturated fatty acids are synthesized.• Some incorporation of C 18:2 into microbial lipids.

Microbial Fatty Acid Synthesis


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)


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


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


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


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)


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.


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



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



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


Summary of fatty acid metabolism in the Summary of fatty acid metabolism in the

liverliver


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.

aulani "biokimia" presentation 6 lipid biochemistry aulanni’am biochemistry laboratory...

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