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1.2 CARBOHYDRATES

1.4 PROTEINS

1.3 LIPIDS

1.5 NUCLEIC ACIDS

1.1 WATER

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1.3 LIPIDS

1.3 Lipids (1 hour)Objectives :

• State the types of lipids: fats, oils, phospholipids and steroids.

• Describe the structure of fatty acids and glycerols.

• Describe the formation and breakdown of triglycerides.

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MAJOR TYPES

OF LIPIDS

Triglycerideseg: Fats & Oils

Phospholipidseg: Lecithin

Steroidseg: Cholesterol & Testosterone

• Organic molecules –contain C, H, O –but proportion of O is lower than in

carbohydrates

LIPIDS

• Molecules that are hydrophobic and insoluble in water (due to many hydrocarbons)

• But may dissolve in organic solvents

(eg: acetone & benzene)

LIPIDS

• Main types:–triglycerides (fats & oils)–phospholipids –steroids

LIPIDS

• The fats (solid at room temperature) & oils (liquid at room temperature)

• Also known as triacylglycerol• Composed of 3 fatty acids & 1 glycerol

* R = hydrocarbon chain

TRIGLYCERIDES

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• A fatty acid (RCOOH) consists of a long linear hydrocarbon chain with a carboxyl group (-COOH) at one end

Fatty Acids

Fatty Acid Molecule

Long hydrocarbon chainCarboxyl group

R CHOO

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• The fatty acid’s H-C chain is non-polar & hydrophobic

• causing triglycerides to be insoluble in water

Fatty Acids

• Fatty acids can be classified as:i. Saturated fatty acid- no double bond in H-C chain- eg: stearic acid

ii. Unsaturated fatty acid- 1 or more double bonds between

carbons- a double bond produces a kink - eg: oleic acid

A double bond; causing a kink

1 Glycerol

OH

C

C

C

OH

OH

H

H

H

H

H

Glycerols

• A type of alcohol• A glycerol contains

3 C & 3 hydroxyl (OH-) groups

• Each fatty acid joins to glycerol by an ester bond

• Involves condensation

• Specifically for fats, the process is also known as esterification

• Triglyceride can be broken down by hydrolysis

FORMATION & BREAKDOWN OF TRIGLYCERIDES

FORMATION & BREAKDOWN OF TRIGLYCERIDE

Ester bond

condensation

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+ 3 H20

ESTER BOND3 FATTY ACIDS

1 GLYCEROL

1 Glycerol

R 1OH

C

C

C

OH

OH

H

H

H

H

H

3 fatty acids

Components of a triglyceride

CHO

O

R 2CHO

O

R 3CHO

O

R 1O

C

C

C

O

O

H

H

H

H

H

A triglyceride molecule

C

O

R 2C

O

R 3C

O

ester linkage

A triglyceride

Ester linkage

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• The 3 fatty acids of 1 triglyceride may all be the same or they may be different

• Triglycerides can be classified as:i. Saturated triglycerides (fats)- has 3 saturated fatty acids- in solid form at room temperature- eg: butter & most animal fats

TRIGLYCERIDES

ii. Unsaturated triglycerides (oils)- has 1 or more unsaturated fatty acids- in liquid form at room temperature

(the kinks prevent the molecules from packing together closely to solidify)

- eg: corn oil (plant fat) & cod liver oil (fish fat)

TRIGLYCERIDES

• Major components of cell membranes

• Combination of:- 2 fatty acids- glycerol - phosphate group

PHOSPHOLIPIDS

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glycerolPOLAR HEAD

NONPOLAR TAILS

fatty acids

phosphate group

Structure of phospholipid

PHOSPHOLIPIDS

• Phosphate group is –ve in charge • A charged/polar additional molecule is usually

attached to the phosphate group• Causes the phospholipid to have a hydrophilic

(polar) head • The H-C chains of fatty acids form the

hydrophobic (nonpolar) tails

• Many types of phospholipids (based on the fatty acids & additional molecule)

• Eg: lecithin (phosphatidylcholine) which has a choline group attached to the phosphate group

PHOSPHOLIPIDS

Phosphatidylcholine (a type of phospholipid)

• Lipids characterized by a carbon skeleton consisting of 4 fused rings

• Functional groups attached to the rings determine the types of steroids

• Eg: cholesterol & testosterone

STEROIDS

• Cholesterol:- component of cell membranes- precursor for other steroids- may contribute to health problems

(eg: atherosclerosis)

cholesterol

• Testosterone:- male sex hormone (for sperm formation & male secondary sex characteristics)

1. Fats as source of energy- 1 g of fat has twice as much energy as 1 g of a polysaccharide- due to the many C-H bonds in fat

2. Fats & oils as energy storage3. Fats insulate the body against heat &

electric4. Fats cushion vital organs5. Fats provide buoyancy6. Fats transport fat-soluble vitamins (A,D,E,K)

IMPORTANCE OF LIPIDS

7. Phospholipids & cholesterols as components of cell membranes

8. Cholesterols as precursor for other steroids

9. Steroids as sex hormones

IMPORTANCE OF LIPIDS

SESSION 2001 / 2002

Question

• Explain the triglyceride structure.

[6 marks]

References :

• Campbell, 8th edition• Solomon, 9th edition

Next Subtopic….• 1.4 Proteins

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1.2 CARBOHYDRATES

1.4 PROTEINS

1.3 LIPIDS

1.5 NUCLEIC ACIDS

1.1 WATER