main lecture for lipids
TRANSCRIPT
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Lipids
Types of Lipids
Fatty Acids
Fats, and Oils
Chemical Properties of Triglycerides
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Types of Lipids
• Lipids with fatty acids
Waxes
Fats and oils (trigycerides)
Phospholipids
Sphingolipids
• Lipids without fatty acids
Steroids
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Fatty Acids
Long-chain carboxylic acids Insoluble in water Typically 12-18 carbon atoms (even number) Some contain double bonds
corn oil contains 86% unsaturated fatty acids and 14% saturated fatty acids
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Saturated and Unsaturated Fatty Acids
Saturated = C–C bonds
Unsaturated = one or more C=C bonds
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COOH
COOH
palmitoleic acid, an unsaturated fatty acid
palmitic acid, a saturated acid
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Properties of SaturatedFatty Acids
Contain only single C–C bonds
Closely packed
Strong attractions between chains
High melting points
Solids at room temperature
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Properties of UnsaturatedFatty Acids
Contain one or more double C=C bonds Nonlinear chains do not allow molecules
to pack closely Few interactions between chains Low melting points Liquids at room temperature
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Fats and Oils
Formed from glycerol and fatty acids
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+
HO C (CH2)14CH3
O
HO C (CH2)14CH3
O
HO C (CH2)14CH3
O
glycerol palmitic acid (a fatty acid)
CH
CH2 OH
OH
CH2 OH
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Triglycerides (triacylglcerols)Esters of glycerol and fatty acids
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CH
CH2
CH2 O
O
O
C (CH2)14CH3
O
C (CH2)14CH3
O
C (CH2)14CH3
O
ester bonds
+
+
+
H2O
H2O
H2O
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The Lipids: Triglycerides, Phospholipids and Sterols
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Lipids Objectives
• 1. Understand the chemical composition and differences between fats
• 2. Explain the structural and functional processes of triglycerides, phospholipids, and sterols
• 3. Describe the process of fat digestion and absorption• 4. Discuss the different types of lipoproteins in the body• 5. Clarify the recommended intakes of fat and essential fatty
acid requirements to meet daily nutritive needs• 6. Describe the health-risk factors with over consumption of
lipids in the diet
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Fatty Acids
• The Length of the Carbon Chain– long-chain, medium-chain, short-chain
• The Degree of Unsaturation– saturated, unsaturated, monounsaturated,
polyunsaturated
• The Location of Double Bonds– omega-3 fatty acid, omega-6 fatty acid
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The Length of the Carbon Chain
Short-chain Fatty Acid (less than 6 carbons)
Medium-chain Fatty Acid(6-10 carbons)
Long-chain Fatty Acid(12 or more carbons)
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Fatty Acids are Key Building Blocks
• Saturated Fatty Acid
• All single bonds between carbons
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Monounsaturated Fatty Acid(MUFA)
One carbon-carbon double bond
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Polyunsaturated Fatty Acid(PUFA)
More than one carbon-carbon double bond
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Location of Double Bonds
• PUFA are identified by position of the double bond nearest the methyl end (CH3) of the carbon chain; this is described as a omega number;
• If PUFA has first double bond 3 carbons away from the methyl end=omega 3 FA
• 6 carbons from methyl end=omega 6 FA
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Eicosanoids: made from EFA
--derivatives of 20-carbon fatty acids;--affect cells where they are made;--have different effects in different cells
--cause muscles to contract and muscles to relax;--help regulate blood pressure, blood clot formation, blood lipids, and immune response;--participate in immune response to injury and infection, producing fever, inflammation, and pain;--include:prostaglandins, thromboxanes, leukotrienes
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Triglycerides
• Structure– Glycerol + 3 fatty acids
• Functions– Energy source
• 9 kcals per gram• Form of stored energy in
adipose tissue– Insulation and protection– Carrier of fat-soluble vitamins– Sensory properties in food
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Triglycerides: lipids composed of three fatty acids attached to a glycerol
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Triglycerides• Food sources
– fats and oils• butter, margarine, meat, baked goods, snack
foods, salad dressings, dairy products, nuts, seeds
– Sources of omega-3 fatty acids• Soybean, canola, walnut, flaxseed oils• Salmon, tuna, mackerel
– Sources of omega-6 fatty acids• Vegetable oils
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Fatty Acids in Common Food FatsFatty Acids in Common Food Fats
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Phospholipids• Structure
– Glycerol + 2 fatty acids + phosphate group
• Functions– Component of cell membranes– Lipid transport as part of
lipoproteins– Emulsifiers– Phosphatidylcholine
• Food sources– Egg yolks, liver, soybeans, peanuts
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Cell membranes are phospholipid bilayers
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Sterols: Cholesterol• Functions
– Component of cell membranes– Precursor to other substances
• Sterol hormones• Vitamin D• Bile acids
• Synthesis– Made mainly in the liver
• Food sources– Found only in animal foods
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Lipid Digestion• In the Mouth
– hard fats begin to melt; lingual lipase
• In the Stomach– gastric lipase--SCFA
• In the Small Intestine– release of CCK; bile-emulsifier; fat drawn into
surrounding watery fluids; intestinal lipases; remove each TG fatty acid; leave glycerol;
• Bile Routes– reabsorbed or trapped by dietary fiber
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Olestra• Sucrose + fatty acids• Indigestible – provides zero
kcals• Reduces absorption of fat-
soluble vitamins• So many fatty acid chains are
crowded around the core, the digestive enzymes cannot find a breaking point
Orlistat (Xenical)* binds to active site of GI lipase and
blocks its activity; thus, lipase can’t break TG down to component parts; TG remains undigested and unabsorbed
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Metabolic Pathways and Energy Production
Metabolism and ATP Energy
Important Coenzymes
Glycolysis
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Metabolism
All the chemical reactions that occur in the cells of our bodies.
Catabolic reactions• Break down large molecules • Provide energy for ATP
Anabolic reactions• Use small molecules to build large ones• Require energy
catabolic
anabolic
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Cell Structure
Typical animal cell• Nucleus• Chromosomes in the nucleus
contain genetic material• Cytoplasm is material
between nucleus and cell membrane
• Mitochondria are where energy-producing reactions occur
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ATP
• Energy is released as food is oxidized• Used to form ATP from ADP and Pi
ADP + Pi + Energy ATP • In cells, energy is provided by the hydrolysis
of ATP
ATP ADP + Pi + Energy
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Structure of ATP
O
OH OH
N
N
N
N
NH2
CH2OPOPOPO-
O O O
O- O- O-
adenine
ribose
adenosine triphosphate ATP
ADP
adenosine diphosphate
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Digestion of Foods
Digestion is the first step of catabolism
• Carbohydrates glucose, fructose, galactose
• Proteins amino acids
• Lipids glycerol fatty acids
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Coenzymes
• Substances that connect metabolic pathways• In reduction, coenzymes accept H atoms• In oxidation, coenzymes remove H atoms
FAD (flavin adenine dinucleotide)
FAD + -CH2-CH2- FADH2 + -CH=CH-
NAD+ (nicotinamide adenine dinucleotide)
NAD+ + -CH-OH NADH + H+ + -C=O
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Glycolysis: Oxidation of Glucose
2ATP2 NAD+
2ADP 2NADH + 2H+
4 ADP
4 ATP
Glucose
two Glyceraldehyde-3-PO4
two Pyruvate
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Glycolysis: Oxidation of Glucose
2 glyceraldehyde-3-phosphate
O
CH2HO
OH
OH
OH
OH PO4O
CH2O
OH
CH2 O PP
OHHO
glucosefructose-1,6-diphosphate
CHO
C OHH
CH2O P
2
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Glycolysis: Oxidation of Glucose
2 NAD+ 2 NADH + 2 H+
2 glyceraldehyde-3-phosphate
CHO
C OHH
CH2O P
2 2
CHO
CH O
CH3
2 pyruvate
2 ADP + 2 Pi 2 ATP
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Glycolysis: Oxidation of Glucose
Glycolysis generates 2 ATP molecules and 2 NADH + 2 H+
Two ATP used in adding phosphate groups to glucose and fructose-6-phosphate (- 2 ATP)
Four ATP generated in direct transfer to ADP by two 3-C molecules (+ 4 ATP)
Glucose + 2 ADP + 2 Pi + 2 NAD+ 2pyruvate + 2 ATP + 2 NADH + 2 H+
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Pathways for Pyruvate
Aerobic conditions O
||
CH3–C –COO- + NAD+ + CoA
pyruvate
O
||
CH3–C –CoA + CO2 + NADH + H+
acetyl CoA
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Pathways for Pyruvate
Anaerobic conditions (No O2 available)
Reduce to lactate to replenish NAD+ for glycolysis
O OH
|| |
CH3–C –COO- + NADH + H+ CH3–CH –COO- + NAD+
pyruvate lactate
enzyme: lactate dehydrogenase
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Lactate in Muscles
• Strenuous exercise leads to anaerobic conditions
• Oxygen in muscles is depleted• Lactate builds up as glycolysis continues• Muscles tire and become painful• Breathing rate increases• Rest repays oxygen debt • Lactate re-forms pyruvate in liver