Biology notes on lipids

2. AP Biology
Lipids: Fats & Oils

3. SPECIFIC OBJECTIVES:
• describe the molecular structure of a
triglyceride and its role as a source of
energy;
• describe the structure of phospholipids
and their role in membrane structure and
function

4. Lipids
Structure of Lipids
Types of Lipids
Chemical Properties of Triglycerides

5. AP Biology 2006-2007
Lipids
long term energy
storage concentrated
energy

6. • heterogeneous group
• organic compounds
• relatively insoluble in water
• soluble in organic solvents such as
ether, chloroform
Propertiesof lipids

7. AP Biology
Lipid
s
♣Lipids are composed of C, H, O
υ long hydrocarbon chains (H-C)
♣“Family groups”
υ fats
υ phospholipids
υ steroids
♣Do not form polymers
υ big molecules made of smaller subunits
υ not a continuing chain

8. Important
physiologic functions
include:
To provide energy for the body
- They serve as structural components
of biological membrane
- To insulate the body and protect
internal organs
-To provide essential fatty acids that are
not found in the human body

9. Classification
■ Simple lipids
a. Fats
b. Waxes
■ Compound Lipids
a. phospholipids
b. Glycolipids
c. Lipoproteins
■ Steroids
a. sterols

11. Simple Lipids: Fats
• Fats are esters of fatty acids with glycerol.
• Most abundant lipid found in nature.
• Best reserve of food material as they
can store unlimited amounts.
• The chemical nature of fat (triglyceride)
consists of three molecules of fatty acids
with one molecule of glycerol.

12. Fat
s
♣ Structure:
υ glycerol (3C alcohol) + fatty acid
♣ fatty acid =
long HC “tail” with carboxyl (COOH) group
“head”
enzyme
H2O
dehydration synthesis
AP Biology

13. AP Biology
Building Fats
♣Triacylglycerol
υ 3 fatty acids linked to glycerol
υ ester linkage = between OH & COOH
hydroxylcarboxyl

14. Glycerol
■ Glycerol C3H8O3
■ There is only one sort
of glycerol
glycerol
C H
2
OH
C HOH
C H 2
OH

15. The synthesis of Fats and Oils
Formed from glycerol and 3 fatty acids
(CH2)14CH3
O
HO C (CH2)14CH3
O
+ HO C
(CH2)14CH3
O
HO C
glycerol palmitic acid (a fatty
acid)
CH2 O
H
CH OH
CH2
O
H

16. The synthesis of Fats and Oils
■ Condensation reaction
■ Forms a triglyceride

17. Triglycerides (triacylglcerols)
CH O
CH2 O
O
CH
2 O C
(CH2)14CH3
C
(CH2)14C
H3
O
C
(CH2)14C
H3 O
Esters of glycerol and fatty acids
ester bonds
+
+
+
H2O
H2O
H2O

18. AP Biology
Condensation reaction
condensation
H2O
enzyme
H2O
enzyme
H2O
enzyme
H2O

19. AP Biology
Fats store energy
♣Long HC chain
υ polar or non-polar?
υ hydrophilic or
hydrophobic?
♣Function:
υ energy storage
♣concentrated
ω all H-C!
♣2x carbohydrates
υ cushion organs
υ insulates body
♣ think whale
blubber!
Why do humans
like fatty foods?

21. Fatty Acids
■ Long-chain carboxylic acids
■ Insoluble in water
■ Typically 12-18 carbon atoms (even
number)
■ Some contain double bonds
■ Essential fatty acids not made in the body
(Linoleic and Linolenic)

22. Fatty Acids
■ Physical and chemical properties of Fats are
determined by their FA structure.
■ Saturated Fatty Acid: general formula= CnH2nO2
■ More informative to write:
CH3(CH2)nCOOH
n varies but generally an even # b/w 14 and 22
Eg. Stearic acid (CH2)16 :. CH3(CH2)16COOH

23. Stearic acid
CH3(CH2)16COOH
Hydrocarbon chain ends with a
carboxyl group
Therefore it can form H-bonds with water
But overall the molecule is insoluble in water
because of the presence of so many CH2
groups

25. Saturated and
Unsaturated Fatty
Acids
Saturated = C–C bonds
Unsaturated = one or more C=C bonds
COOH
palmitic acid, a saturated acid
COOH
palmitoleic acid, an unsaturated fatty acid

26. Properties of
Saturated Fatty
Acids
■ Contain only single C–C bonds
■ Closely packed
■ Strong attractions between chains
■ High melting points
■ Solids at room temperature

27. AP Biology
Saturated fats
♣All C bonded to H
♣No C=C double bonds
υ long, straight chain
υ most animal fats
υ solid at room temp
♣ contributes to
cardiovascular disease
(atherosclerosis)
= plaque deposits

28. Properties of
Unsaturated Fatty
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

29. AP
Biology
Unsaturated fats
♣C=C double bonds in
the fatty acids
υ plant & fish fats
υ vegetable oils
υ liquid at room temperature
♣ the kinks made by
double bonded C
prevent the molecules
from packing tightly
together
Which is best?

32. Saturated vs. unsaturated
saturated unsaturated
AP Biology

33. Fats
■ Solids at room temp
■ Because FA molecules are smaller or
because of presence of no double bonds
■ OILS
■ Liquids at room temp
■ Large FA
■ Presence of one/ more double bonds.

34. Functions of Fatty Acids
1. Fats yield twice as much energy as
carbohydrates because they contain
relatively little O2
Used as a source of energy when needed
But they require more O2 to respire them
than CHO’s so they are not the primary
energy source
They are usually stored energy

35. Functions of Fatty Acids
2. Insulator:
Because it conducts heat energy slowly
Animals living in cold climates have
extensive fats stores (sub-cutaneous)
3. Buoyancy
4. Protection

36. Functions of Fatty Acids
5. Structure of Plasma membrane when
combined with phosphoric acid

38. Glycolipids
■ Associations of lipids with carbohydrates
■ Carbohydrates form a polar head to the
molecule.
■ Found in membranes
■ Help in cell recognition

39. Phospholipids
■ Most abundant lipids in cell
membranes
■ Control cell permeability
■ Consist of a highly polar head
(phosphate) and a nonpolar tail.

40. Phospholipids
■ In living things they have 2 main
functions
1. In membrane structure
2. Transport of fat between gut and liver.
3. Since they have both hydrophobic and
hydrophillic ends.

41. AP
Biology
Phospholipids
♣ Structure:
υ glycerol + 2 fatty acids + PO4
♣ PO4 = negatively charged
It’s just like a
penguin…
A head at one end
& a tail
at the other!

42. AP
Biology
Phospholipids
υ PO4 head =
interaction with H2O
is complex & very
important!
“repelled by water”
“attracted to water”
υ split “personality”
Come here,
No, go away!
Come here,
No, go away!
♣ Hydrophobic or
hydrophilic?
υ fatty acid tails =hydrophobic
hydrophillic

43. Phospholipids
■ Formed when one of FA groups is
replaced by a phosphate group.
■ Phosphate group is ionised and henced
soluble in water
■ Hence phospholipids are both hydrophobic
and hydrophillic.
■ At oil water interfaces they are oriented
with hydrophobic groups in oil and
hydrophillic groups in water.

46. AP
Biology
Phospholipids in water
♣Hydrophilic heads “attracted” to
H2O
♣Hydrophobic tails “hide” from H2O
υ can self-assemble into “bubbles”
♣bubble = “micelle”
♣can also form a phospholipid bilayer
bilayer
water
water

47. AP
Biology
Why is this important?
♣Phospholipids create a barrier in water
υ define outside vs. inside
υ they make cell membranes!
Tell them
about soap!

49. Extra knowledge
:)

50. Micelles

51. Micelles

54. Waxes
■ Esters of FA’s but with complex alcohols
■ Used as water proofing materials by both
plants and animals
■ Where in animals?
■ Where in plants?
Arthropod cuticles, vertebrate skin, bird
feathers and mammalian fur.

55. Steroids
■ Apart from fats and oils , steroids are the
most important lipids in animals and
plants
■ Structure = 4 interlinked rings of C-atoms.
■ Best known steroid = cholesterol that has
received bad publicity.
■ However is cholesterol is essential…….

56. AP Biology
Steroids
♣Structure:
υ 4 fused C rings + ??
♣different steroids created by attaching different
functional groups to rings
♣different structure creates different function
υ examples: cholesterol, sex hormones
cholesterol

57. Cholesterol
■ Most abundant steroid in the body
■ Complex rings of C-atoms.
■ Cholesterol found in the body as
hormones, Vitamin D, bile salts, Myelin
sheath, brain, cell membrane
CH3
HO
CH3
CH3
CH3
CH3

58. AP
Biology
Cholesterol
♣Important cell component
υ animal cell membranes
υ precursor of all other steroids
♣ including vertebrate sex hormones
υ high levels in blood may contribute to
cardiovascular disease

59. AP Biology
Cholesterol
helps keep
cell membranes
fluid & flexible
Important component of cell membrane

60. AP Biology
From Cholesterol → Sex Hormones
♣ What a big difference a few atoms can
make!

63. The END

64. Other Lipids
■ Terpenes like Vitamins A, E, K-compounds
similar to steroids but smaller.
■ Other terpentines- rubber, turpentine,
plant growth hormones.
■ Suberin-tree bark
■ Cutins-cuticle on trees

65. AP Biology 2006-2007
Let’s build some
Lipids!