LOGO

Course lecturer :

Jasmin Šutković

7 December 2015

Organic Chemistry – FALL 2015

Lecture 7Lipids

CHAPTER OUTLINE International University of Sarajevo

19.1 Introduction to Lipids19.2 Fatty Acids19.3 Waxes19.4 Triacylglycerols—Fats and Oils19.5 Hydrolysis of Triacylglycerols19.6 Phospholipids19.7 Cell Membranes19.8 FOCUS ON HEALTH & MEDICINE:Cholesterol, the Most ProminentSteroid19.9 Steroid Hormones19.10 FOCUS ON HEALTH & MEDICINE:Fat-Soluble Vitamins19.11 FOCUS ON HEALTH & MEDICINE:Prostaglandins and Leukotrienes

Book chapter 19

Introduction

CHAPTER 19 is the first of four chapters that deal with the chemistry of biomolecules, organic molecules found in biological systems.

Chapter 19 focuses on lipids, biomolecules that contain many carbon–carbon and carbon–hydrogen bonds, making them soluble in organic solvents and insoluble in water

Introduction

Lipids are biomolecules that are soluble in organic solvents and insoluble in water.

They are found in many varieties, so having many functions!

Common lipids include triacylglycerols in vegetable oils, cholesterol in egg yolk, and vitamin E in leafy greens.

The word lipid comes from the Greek word lipos for fat.

Lipids

Basic functions in the body Store and provide energy

– Fats provide 9 kcal per gram

Provide insulation Help manufacture steroids and bile salts Play a role in transporting fat-soluble nutrients

in the blood Used to manufacture major sex hormones Key to the structure of cell membranes

Fatty Acids

Building blocks for triglycerides and phospholipids

A chain of carbon and hydrogen atoms with a carboxyl group at the alpha end and a methyl group at the omega end

Figure 5.1

Fatty Acids

Higher ratio of carbon and hydrogen to oxygen than in carbohydrates and protein 9 kilocalories per gram of fat

20 different fatty acids with varied length, saturation, and shape

Fatty Acids Vary in Length

Short-chain fatty acids Two to four carbons Weak attraction Liquid at room temperature

Medium-chain fatty acids Six to ten carbons

Fatty Acids Vary in Length

Long-chain fatty acids

12 or more carbons Most common type of fatty acid in foods Strong attraction Solid at room temperature

Fatty Acids Vary in Saturation

Saturated All the carbons on the fatty acid are bound to

hydrogen Solid at room temperature Higher melting point

Fatty Acids Vary in Saturation

Unsaturated Some carbons on fatty acid form a double

bond with each other instead of binding to hydrogen• Monounsaturated fatty acids (MUFA)

– Has one double bond

• Polyunsaturated fatty acid (PUFA)– Has two or more double bonds

Liquid at room temperature Lower melting point

Saturated and Unsaturated Fatty Acids Help Shape Foods

Figure 5.3

Fatty Acids Differ in Double-Bond Location

The location of the first double bond in unsaturated fatty acids effect the omega-3 fatty acid and omega-6 fatty acid

Omega-3 fatty acid First double bond is between the third and

fourth carbon from the omega end Example: Alpha-linolenic acid

• One of the two essential fatty acids

Fatty Acids Differ in Double-Bond Location

Omega-6 fatty acid

First double bond is between the sixth and seventh carbon from the omega end

Example: Linoleic acid• One of the two essential fatty acids

The Omega Fatty Acids

Figure 5.4

Figure 5.5

Fatty Acids Vary in Shape

Unsaturated fatty acids form two different shapes

Portion of Figure 5.7

Triglycerides

Three fatty acids connected to a glycerol backbone

Caution:High levels in the blood

are a risk factor for

heart disease

Triglycerides

Most common lipid in both foods and the body Make up about 95% of lipids found in foods Functions

Add texture Makes meats tender Preserves freshness Stores as adipose tissue

for energy

Hydrophilic on one end; hydrophobic on the other Make up the phospholipid bilayer in the cell membrane Synthesized by the liver

Phospholipids

Portion of Figure 5.8

Phospholipids’ Role in Cell Membranes

Figure 5.9

Sterols

More complex than phospholipids or triglycerides Four connecting rings of carbon and hydrogen

Do not provide energy Cholesterol is the best known sterol

Found in every cell in the body Helps with numerous body processes

Phytosterols – major plant sterols

Figure 5.11

Quick Review

Figure 5.12

Quick Review

Triglycerides Found in the body Stored in the adipose tissue Major source of energy

Phospholipids An important part of cell membrane structure Lecithin

• Important to cell membrane

• Used as a food emulsifier

Sterols Do not contain fatty acids Do not provide energy

What Happens to the Lipids You Eat?

Lipids from foods Fat, phospholipids, and sterols

Digested to Free fatty acids, glycerol, and monoglycerides

With the aid of the enzyme lipase

Figure 5.13

Figure 5.13

Figure 5.13

Most Fat Is Digested and Absorbed in the Small Intestine

Lipoproteins Transport Fat Through the Lymph and Blood

Lipoproteins (transporter proteins) Chylomicrons Very low-density lipoproteins (VLDLs) Low-density lipoproteins (LDLs) High-density lipoproteins (HDLs)

Lipoproteins Transport Fat Through the Lymph and Blood

VLDLs, LDLs, and HDLs Globular molecule with a lipid center surrounded

by a plasma membrane Density determines function More protein, higher density

Very low-density lipoproteins (VLDLs) Become LDLs

LDLs: “bad” cholesterol HDLs: “good” cholesterol HDL and LDL levels can be used to determine the

health of arteries

The Roles of VLDL, LDL, and HDL Lipoproteins

Figure 5.18

Uses of Fat and Cholesterol

Source of energy Form body structures Regulate metabolism Enhance absorption of fat-soluble vitamins Provide insulation to help regulate body

temperature Cushion major organs

Fat Is Used as Energy

Fat Provides concentrated source of kilocalories

• 9 kilocalories per gram

Readily available when the body needs energy Body’s main source of energy throughout the

day

Fat Is Used as Energy

Fat Body has an unlimited ability to store excess

energy as fat in adipocytes• Fat cells have the capacity to enlarge as much as

1,000 times their original size• Body has the ability to produce additional fat cells

Fat Is Used as Energy and Helps Absorb Lipid Compounds

Preferred source of energy for the heart, liver, and muscles Cannot sustain life alone Needs glucose

Only glycerol can be used for gluconeogenesis

Several essential nutrients require dietary fat for absorption 20 grams per day are needed to stimulate chylomicrons that

transport fat-soluble vitamins

Fat Helps Insulate and Protect

Fat in subcutaneous tissue Insulates body Maintains body temperature

Fat protects bones and vital organs from trauma Too much fat eliminates the protective benefit

Cholesterol Is Used to Make Bile, Hormones, and Vitamin D

Cholesterol

A structural part of the cell membrane A precursor to vitamin D A precursor to bile acid Precursor for sex hormones such as estrogen and

testosterone

How Much Fat Do We Need Each Day?

Overall intake of fat in the U.S. is higher than it should be

Acceptable Macronutrient Distribution (AMDR) recommendation 20–35% of daily kilocalories should come from

fat

For heart health Consume no more than 10% of total

kilocalories from saturated fat Limit trans fats to < 1%

Essential Fatty Acid Recommendations

Adequate Intake (AI) for the essential fatty acids

Alpha-linolenic acid• Men 1.6 grams/d• Women 1.1 grams/d

Linoleic acid• Men 17 grams/d• Women 12 grams/d

*Currently Americans only consume about 0.1–0.2 grams/d of EPA and DHA

Best Food Sources of Fat

Figure 5.20

Sources of unsaturated fats

Food Sources of Omega-3 Fatty Acids

Figure 5.21

Where’s the Saturated Fat in Foods?

Figure 5.22

• Accumulate in the arteries

Fat and Cholest

erol

• Blood flow is impeded

Arteries narrow

• Not enough oxygen to the heart

• CHEST PAIN

Decrease oxygen

and nutrients

What Is Heart Disease and What Factors Increase Risk?

Cardiovascular disease is the number-one killer of adults in the world…

Atherosclerosis

Figure 5.24

For a healthy life do….

For optimal long-term health a diet should include a proper balance of all nutrients including fat

There are different types of lipids, some essential and others not required from foods

Goal Consume mostly unsaturated fats Limit amount of saturated and trans fats

A plant-based diet plentiful in whole grains, fruits, and vegetables, with some low-fat dairy and lean meats, poultry, fish, and vegetable oil will be high in fiber and lower in saturated fats, trans fats, and dietary cholesterol

Types of lipids

Lipids can be categorized as hydrolyzable or nonhydrolyzable.

Two types of fatty acids :

Saturated fatty acids have no double bonds in their long hydrocarbon chains.

Unsaturated fatty acids have one or more double bonds in their long hydrocarbon chains. Generally, double bonds in naturally occurring fatty acids are cis.

WAXES

Waxes are the simplest hydrolyzable lipids.

Waxes are esters (RCOOR') formed from a fatty acid (RCOOH) and a high molecular weight alcohol (R'OH).

Because of their long nonpolar carbon chains, waxes are very hydrophobic.

They form a protective coating on the feathers of birds to make them water repellent, and on leaves to prevent water evaporation.

Lanolin is a wax thatcoats the wool fibers of sheep.

Beeswax, a complex mixture of over 200 different compounds, contains the wax myricyl palmitate as its major component

TRIACYLGLYCEROLS—FATS AND OILS

Animal fats and vegetable oils, the most abundant lipids, are composed of triacylglycerols

Triacylglycerols, or triglycerides, are triesters formed from glycerol and three molecules of fatty acids.

PHOSPHOLIPIDS

Phospholipids are lipids that contain a phosphorus atom. Two common types of phospholipids are phosphoacylglycerols

and sphingomyelins. Both classes are found almost exclusively in the cell membranes of

plants and animals .

Phosphoacylglycerols

Phosphoacylglycerols (or phosphoglycerides) are the second most abundant type of lipid.

They form the principal lipid component of most cell membranes.

SPHINGOMYELINS

Sphingomyelins, the second major class of phospholipids, differ in two important ways from the triacylglycerols and the phosphoacylglycerols.

1. Sphingomyelins do not contain a glycerol backbone. Instead, sphingomyelins are derived from sphingosine.

2. Sphingomyelins do not contain an ester. Instead, their single fatty acid is bonded to the carbon backbone by an amide bond.

Cholesterol – most abudant steroid

Steroids are lipids whose carbon skeletons contain three six-membered rings and one five membered ring.

Fat soluble vitamins

The fat-soluble vitamins are lipids.

The four fat-soluble vitamins—A, D, E, and K—are found in fruits and vegetables, fi sh, liver, and dairy products. Although fat-soluble vitamins must be obtained from the diet, they do not have to be ingested every day.

Excess vitamins are stored in adipose cells, and then used when needed.

Table 19.5 summarizes the dietary sources and recommended daily intake of the fatsoluble vitamins.

Few topics for the coming projects…

Saturates and unsaturated fats in our food Biofuels Cell membrane structure Transport across the cell membrane Cholesterol and Lipoproteins Steroid hormones Asthma – steroids and leukotriens?

Short guidelines…

Power point presentation 4% 8 to 15 slides

Written Paper 4% 10 pages (double space: Introduction, main

body and conclusion, don’t forget reference and citations)

Answering of my and your colleagues questions 2%

Presentation week: 4 i 6th January 2016

Readings

Chapter 19 – pages : 569 -610

14th Dec.2014 Quiz II :Only lectures 6, 7 and 8 !

Read the book and dont forget to start to think about your projects- select a topic by 21th December or I will find it for You…