Lipids

1
Lipids
2
Lipids

• Known as fats
• Used to store energy and carbons in body
• No common structural feature
• Characterized by solubility
• Lipid - bioorganic substance found in living
  organisms that is insoluble (or slightly soluble)
  in H2O but soluble in organic solvents

3
Classes of Lipids
fatty acids
Fat soluble vitamins
eicosanoids

steroids
triacylglycerols
glycolipids
waxes
phospholipids
fatty acids absent
4
Functions

• Energy source
• storage compounds (triacylglycerols)
• Hydrophobic barriers
• membrane constituents (phospholipids
  glycoplipids)
• Functional
• protective coverings (waxes)
• regulatory properties
• hormones (steroids, prostaglandins, vitamins)
• signalling

5
Fatty Acids

• Naturally occurring carboxylic acids
• Insoluble in water
• Typically an even number of carbons
• Are either long (C12-C26), medium (C8-C10), or
  short (C4-C6)
• May contain double bonds

6
Saturated and Unsaturated Fatty Acids

• Saturated CC bonds
• Unsaturated one or more CC bonds

C
O
O
H
p
a
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c

a
c
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d
,

a

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C
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H




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7
Structures

• Saturated fatty acids
• Fit closely in regular pattern
• Monounsaturated fatty acids
• Cis double bond

C
O
O
H
C
O
O
H
C
O
O
H


H
H
C
C
H




C
O
O
c
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s

d
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b
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8
Structures

• Polyunsaturated fatty acids

9
Structure Notation

• Consists of using shorthand notations
• A B where A is the of carbons and B is the
  number of double bonds
• If double bonds are present, ?x (delta) denotes
  the position of the double bond
• Remember that carboxylic acids are numbered such
  that the carboxyl carbon is 1

10
Fatty Acid Structure

• Families of unsaturated fatty acids
• Named by starting the numbering at the
  noncarboxyl end of the carbon chain
• Position of the double bond denoted by ?-x
  (omega) where x is the position of the first
  double bond

11
Properties of SaturatedFatty Acids

• Contain only single CC bonds
• Closely packed
• Strong attractions between chains
• High melting points
• Solids at room temperature

12
Properties of UnsaturatedFatty Acids

• Contain one or more double CC bonds
• Nonlinear chains do not allow molecules to pack
  closely
• Few interactions between chains
• Low melting points
• Liquids at room temperature

13
Fatty Acids
14
Triacylglycerols

• Triacylglycerol lipid used as an energy-storage
  material in the body
• Stored in adipocytes and are more efficient at
  storing energy than glycogen
• Most abundant type of lipid in the body
• Are triesters
• Can be simple or mixed
• Also called triglycerides

15
Triacylglycerols

• Esterification rxn of glycerol and 3 fatty
  acids

O
C
H
O
H
H
O
C
(
C
H
)
C
H
2
2
1
4
3
O

H
O
C
(
C
H
)
C
H
C
H
O
H
2
1
4
3
O
H
O
C
(
C
H
)
C
H
O
H
C
H
2
1
4
3
2
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16
Triacylglcerols

• Product of esterifaction

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s
t
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r

b
o
n
d
s
O
C
H
O
C
(
C
H
)
C
H

H
O
2
2
1
4
3
2
O
C
H
O
C
(
C
H
)
C
H
H
O

2
1
4
3
2
O
C
H
O
H
O
C
(
C
H
)
C
H






2
2
2
1
4
3
17
Fats and Oils

• Fats and oils are both naturally occurring
  complex mixtures of triacylglycerol molecules
• Fat a solid or semi-solid at room temp and
  generally obtained from animal sources
• Are generally saturated fatty acids
• Oil a liquid at room temp and generally
  obtained from plant or fish sources
• Are generally unsaturated fatty acids

18
Dietary Fats

• Fat is a general term used to describe all
  triacylglycerols
• Bad fat is saturated fats and all unsaturated
  fats are good fats
• Essential fatty acid fatty acid required by the
  body and obtained from your diet since the body
  cannot synthesize them adequately
• Includes linoleic and linolenic acids

19
Properties of Triglycerides

• Hydrogenation
• Unsaturated compounds react with H2
• Ni or Pt catalyst
• CC bonds CC bonds
• Results in an increase in the melting point
• Hydrolysis
• Split by water and acid or enzyme catalyst
• Produces glycerol and 3 fatty acids if complete

20
Hydrogenation
O





C
(
C
H
)
C
H
C
H
(
C
H
)
C
H
C
H
O
2
5
2
7
3
2
O
N
i
(
C
H
)
C
H
C
H
(
C
H
)
C
H

H
3
C
H
O
C
2
5
2
7
3
2




O
(
C
H
)
C
H
C
H
(
C
H
)
C
H
C
H
O
C









2
5
2
7
3
2
21
Product of Hydrogenation
O

• Hydrogenation converts double bonds in oils to
  single bonds. The solid products are used to
  make margarine and other hydrogenated items.

C
H
O
C
(
C
H
)
C
H
2
2
1
4
3
O
C
H
O
C
(
C
H
)
C
H
2
1
4
3
O
C
H
O
C
(
C
H
)
C
H
2
2
1
4
3
22
Hydrolysis

• Triglycerides split into glycerol and three
  fatty acids (H or enzyme catalyst)

23
Saponification

• Hydrolysis with a strong base
• Triglycerides split into glycerol and the salts
  of fatty acids
• The salts of fatty acids are called soaps

24
Saponification

25
Soaps

• Soaps clean by acting as emulsifying agents
• their long hydrophobic hydrocarbon chains cluster
  so as to minimize their contact with water
• their polar hydrophilic carboxylate groups remain
  in contact with the surrounding water molecules
• driven by these two forces, soap molecules
  spontaneously cluster into micelles

26
Complex Lipids
27
Cholesterol

• Membrane lipid that is a steroid and a specific
  molecule not a family of compounds
• Steroid lipid whose structure is based on a
  fused-ring system composed of 3 6-membered rings
  and a 5 membered ring (called the steroid
  nucleus)

C
D
A
B
28
Cholesterol

• Most abundant steroid in the body
• Is 27 carbon molecule that is in cell membranes
  and a precursor of other steroid-based lipids

29
Cholesterol in the Body

• Present in cell membranes, nerve and brain
  tissue, and all fluids
• Obtained from diet and synthesized by the liver
  and intestine
• Is distributed by a carrier system called
  lipoproteins
• Includes LDLs (low density lipoproteins), which
  carry cholesterol from the liver, and HDLs (high
  density lipoproteins), which carry cholesterol
  from tissues back to the liver
• LDLs are bad and HDLs are good
• Imbalance results in an increase in blood
  cholesterol levels

30
Steroid Hormones

• Are biochemical substances that are chemical
  messengers in cells and derived from cholesterol
• Examples include sex hormones and
  adrenocorticoids hormones
• Sex hormones include male and female sex
  hormones and progestins, pregnancy hormones
• Adrenocorticoids control ionic balance in cells
  and glucose metabolism

31
Sex Hormones