Lipids are organic molecules that contain long hydrocarbon chains and are insoluble in water. The three main types of lipids in the human body are triglycerides, phospholipids, and steroids. Triglycerides are formed from glycerol and fatty acids and are used for energy storage. Phospholipids make up cell membranes and are formed from glycerol, fatty acids, phosphate, and nitrogen compounds. Steroids like cholesterol are important for cell signaling and hormone production but high levels can increase heart disease risk. Lipids play important structural and energy storage roles but too much can lead to obesity and heart problems.

1. B4: LIPIDS
FATS!!

2. General Info. - Lipids
 Organic molecules with long hydrocarbon
chains
 Contains oxygen, carbon, and hydrogen
 Soluble in non-polar solvents
 Organic solvents
 Insoluble in water
 Occur in only 3 forms

3. B.4.1: Compare the composition of the 3
types of lipids found in the human body.
 3 types
 Triglycerides (aka fats and oils)
 Phospholipids (aka lecithin)
 Steroids (aka cholesterol)

4. B.4.1. (Triglycerides)
 Fat vs. Oil
 Fat  saturated (Solid)
 Oil  unsaturated (Liquid)
 Triglycerides are formed by
CONDENSATION reaction between
propane-1,2,3-triol (glycerol) and long chain
carboxylic acids (fatty acids)

5. B.4.1. (Triglycerides)
 Can vary in length!
 Always EVENLY numbered in length!

6. B.4.1. (Phospholipids)
 Integral part of all cell membranes
 Made of four components
 GLYCEROL linked to TWO FATTY ACIDS and a PHOSPHATE
GROUP by esterification; phosphate is linked to a NITROGEN
CONTAINING ALCOHOL

7. B.4.2. (Phospholipids)
Fatty Acid Chain
Glycerol
Choline Group

8. B.4.1. (Steroids)
 Also known as CHOLESTEROL
 HighDensity Lipid (HDL)
 Low Density Lipid (LDL)
 Organic structure of 4 rings (always have 20
carbon atoms)

9. B.4.2: Outline the difference between HDL
and LDL cholesterol and outline its
 Both are LIPOPROTEINS
 Have SAME structure
 LDL transports CHOLESTEROL TO THE
ARTERIES where it lines the walls.
 Saturatedfats
 Cardiovascular disease
 HDL can REMOVE cholesterol from the
arteries and transport it back to the

10. B.4.3: Describe the difference in structure
between saturated and unsaturated fatty
 Saturated Fatty Acid
 Every carbon has the maximum amount of
hydrogens (SINGLE bonds only)
 Unsaturated Fatty Acid
 DOUBLE bonds
 LOWER MELTING POINT
 Creates a “kink” or a bend
 STEARIC EFFECT (relevant to shape): the
interjection of double bonded C atoms prevent
the fatty acid molecules from approaching
each other closely and hence interacting via
Van der Waals’ forces.

11. B.4.3. (Saturated vs.
SATURATED UNSATURATED
Type Molec. Structure Phys. Structure Van der Waals Mel7ng Points
Saturated All single bonds C‐C Straight chains Greater (more High (solid at room
atoms)  stronger interac9on temp)
Unsaturated One C=C (mono‐) or Double‐bonds Lesser (fewer Low (liquid at room
several C=C (poly‐) à kinked chain atoms)  weaker interac9on temp)

12. B.4.4: Compare the structures of the 2 essential
fatty acids linoleic (omega-6) and linolenic
 Linoleic (ω‐6 faJy acid)
 POLY-UNSATURATED fatty acid
 Carboxylic acid with an 18 carbon chain and two cis-
double bonds (C=C)
 cis means on the same side
 The first double bond is located at the 6th carbon from the
methyl end (aka- the omega end) and the second is located
at the 9th.
Carboxylic Acid
omega end

13. B.4.4. (Linolenic (ω‐3 faJy acid)
 POLY-UNSATURATED fatty acid
 Carboxylic acid with an 18 carbon chain and THREE cis- double
bonds (C=C)
 The first double bond is located at the 3rd carbon from the
methyl end (aka- the omega end), the second is located at the
6th, and the third is located at the 9th. (Multiples of 3!)
Carboxylic Acid
omega end

14. B.4.5: Define the term iodine number and
calculate the number of C=C double bonds in
 Unsaturated fats can undergo addition
reactions
 One mole of Iodine reacts with one mole of
double bonds
 Iodine is colored
 As reaction takes place, purple color
disappears
 Fats can be described by their iodine
number

15. B.4.5. (Calculating Iodine
 2 Titrations
 IBr and ICl mixed in glacial acetic acid  Iodine
is formed (YELLOW)
 IBr and Icl mixed in glacial acetic acid + sample of
FAT in solution
 Titrated w/ SODIUM THIOSULFATE
 Concentration of iodine is determined
 Difference of concentration of AMOUNT OF
IODINE (in 2 titrations)
 Ratio of FAT: IODINE

16. B.4.6: Describe the condensation of
glycerol and 3 fatty acid molecules to
 Condensation  WATER is formed
 ESTERIFICATION between the glycerol
backbone and 3 fatty acid molecules
 http://nutrition.jbpub.com/resources/
animations.cfm?id=10&debug=0
 Requires 3 FATTY ACIDS +
1 GLYCEROL
Glycerol (3 carbon
backbone)

17. B.4.6. (Formation of

18. B.4.7: Describe the enzyme-catalyzed
hydrolysis of triglycerides during
 Fats and oils are hydrolyzed by enzymes to
GLYCEROL and FATTY ACIDS
 Enzymes known as LIPASES
 This is the REVERSE of the formation of fats
 After hydrolysis, the products are broken down
further by a series of REDOX REACTIONS
 Produces CARBON DIOXIDE, WATER, and
ENERGY
 Fats are in a LESS OXIDIZED form than
carbohydrates so the same weight of fat

19. B.4.7. (Triglycerides during

20. B.4.8: Explain the higher value of fats as
compared to carbohydrates.
 Fats
 Long hydrocarbon chains
 Mass mainly from CARBONS (oxygen: carbon ratio
small)
 Carbohydrates
 Contain EQUAL proportions of carbon and
oxygen and TWICE AS MUCH HYDROGEN
atoms
 Fats and Carbohydrates  metabolize
 CO2 and H2O (products)

21. B.4.8. (Reasoning for Higher
 Amount of OXIDATION that takes place as the
compounds are converted to CO2 and H2O (Fat
needs more oxidation to occur)
 In fats most carbons are bonded to hydrogen atoms, so
when fats are metabolized they form more new C-O
bonds, releasing more energy than carbohydrates
(where C-O bonds exist)
 The bond enthalpy of the C-O bond is high, so when it
forms a large amount of energy is released
 Fat molecules require about half as much
oxygen for the same number of carbon atoms
 OXIDATION OF FATS IS LONGER, but produces more
energy

22. B.4.9: Describe the important roles of lipids in
the body and the negative effects they can
 Cell Membranes (structurally)
 Phospholipids consist of a polar, hydrophilic
phosphate ‘head’ and two hydrophobic fatty
acid ‘tails’.
 Phospholipid will always point toward water
 creates the structure of the
PHOSPHOLIPID BILAYER
 Energy Storage
 TRIGLYCERIDE LIPIDS

23. B.4.9. (“Good” Roles of Lipids)
 Insulation and Protects Organs
 Adipose tissue (ADIPOCYTES)
 Lipids are COVALENT COMPOUNDS that do
not conduct heat or electricity easily.
 Steroid Hormones
 Cell-signaling
 HORMONE-PROTEIN COMPLEXES + frequency
 Ω‐3 faJy acids reduce the risk of heart
disease
 increasing circulation and breaking down the

24. B.4.9. (“Bad” Roles of Lipids)
 Cholesterol + LDL
 A high-cholesterol diet can result in a high
concentration of LDLs in the bloodstream
(hardening and blocking)
 Obesity
 Carbohydrates not metabolized as turned into
lipids via adipocytes (leading to increased body
mass)
 Increased body mass leads to strains on other
body parts