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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

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

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

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

The Lipids: Triglycerides, Phospholipids and Sterols

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

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

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)

Fatty Acids are Key Building Blocks

• Saturated Fatty Acid

• All single bonds between carbons

Monounsaturated Fatty Acid(MUFA)

One carbon-carbon double bond

Polyunsaturated Fatty Acid(PUFA)

More than one carbon-carbon double bond

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

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

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

Triglycerides: lipids composed of three fatty acids attached to a glycerol

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

Fatty Acids in Common Food FatsFatty Acids in Common Food Fats

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

Cell membranes are phospholipid bilayers

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

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

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