Lecture 1. Introduction to Biochemistry

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Lecture-5
LIPID
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Fatty acids in food saturated vs unsaturated
Fatty Acids
Source Lauric/Myristic Palmitic Stearic
Oleic Linoleic
Beef 5 26-32 20-25
37-43 2-3 Milk 25 12
33 3 Coconut 74 10
2 7 Corn 8-12
3-4 19-24 34-62 Olive 9
2 84 4 Palm 39 4
40 8 Soybean 9 6
20 52 Sunflower 6 1 21
66
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Lipids
Lecture 15. Lipids
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• Lipids have low solubility in water
• Lipids are amphipathic (polar and nonpolar)
• Lipids are a principle component of biological
  membranes
• highly reduced forms of carbon yield large
  amount of energy upon oxidation in metabolism

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Roles of Lipids

• Structural elements (phospholipids, cholesterol)
• Energy storage (fatty acids, triacylglycerols)
• Hormones ( sex hormones e.g. Estrogen,
  testosteron)
• Enzyme cofactors (coenzyme A)
• Electron carriers (coenzyme Q, plastpquinone)
• Light-absorbing pigments (carotenoids)
• Emulsifying agents (bile salts)
• Intracellular messengers (phosphatidyl inositol)

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Spontaneously Formed Lipid Structures

• Hydrophobic interactions are important

• Lipid is an amphipathic molecule,
• but rarely exists as a monomer.

air
water
monolayer
Lipid bilayer
Micelle
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What is soap ?
TAG 3KOH (NaOH) ? 3RCOO-K glycerol

• FA chains can dissolve in oils while charged
  carboxyl
• group dissolves in water
• Forms a mixed micelle which can remove oils
• Soap form precipitates with divalent cations
• (reduces efficiency)
• Detergent (modified FAs) do not precipitate with
  
• calcium, used as better cleaning agents.

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Lipids and the Structure of the Plasma Membrane
To minimize interactions of FA chains
(non-poplar), phospholipids aggregates form a
bilayer structure.
glycolipid
Polar head hydrophobic tail
Integral protein
cholesterol
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Fatty Acids as Stored Energy

• Fatty acids are the bodys principal form of
  stored energy
• Carbon almost completely reduced as CH2
• Principal sources dairy products, meats
  Triacylglycerols, phospholipids, sterol esters

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Fatty acids (FAs)
Structure and nomenclature

• Basic formula CH3(CH2)nCOOH
• Carboxylic acids with hydrocarbon chains of
• 4-24 carbons
• Free FAs are found in trace quantities in cells
  
• FAs are either
• (i) part of a lipid molecule
• (ii) complexed to a carrier protein
• (e.g. albumin on blood)
• Saturated or unsaturated

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Common Fatty Acids

• Saturated fatty acids
• Lauric acid 120
• Myristic acid 140
• Palmitic acid 160
• Stearic acid 180
• Unsaturated fatty acids
• Palmitoleic acid 161
• Oleic acid 181
• Linoleic acid 182
• A-linoleic acid 183 (9,12,15)
• G-linoleic acid 183 (6,9,12)

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Some Naturally Occurring Fatty Acids
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Naming of fatty acids
C18
?
?
?
9
10
CH3-(CH2)7-CHCH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH
Cis ?9
180, stearic acid octadecanoic
acid 181 (?9), oleic acid
octadecenoic acid 182 (?9,12), linoleic acid
octadecadienoic acid 183
(?9,12,15), ?-linolenic acid
octadecatrienoic acid
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Triglycerols (triglycerides)
Lecture 15. Lipids
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• Triglycerols consist of a glycerol esterified
  with three fatty acids
• If all fatty acid chains are the same, the
  molecule is called triacylglycerol (e.g.,
  tristearin)

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• Fats are largest subgroup of lipids
• Made up of fatty acids and glycerol

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Naturally occurring fatty acids
There is a common pattern in the location of
double bonds Unsaturated FA ?9, ?12, ?15
Polyunsaturated FA double bonds
are never conjugated and are seperated
byCH2 (-CHCH-CH2-CHCH-)n
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Saturated
b. Unsaturated
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Structural Consequences of Unsaturation
Lecture 15. Lipids
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• Saturated chains pack tightly and form more
  rigid, organized aggregates (i.e., membranes)
• Unsaturated chains bend and pack in a less
  ordered way, with greater potential for motion.

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Saturated vs. Unsaturated Fats

• Saturated fats have no CC bonds
• Saturated with hydrogen
• Unsaturated fats have CC bonds
• May have more than one double bond
• Can add more hydrogen to fats
• React readily with iodine, bromine, and chlorine

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Iodine Number

• Iodine Number number of grams of iodine consumed
  by 100 g of fat

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Waxes

• - Esters of long chain fatty acids
• (C14-36) with long chain
• (C16-30) alcohols
• - High melting points (60-100?C)
• Energy storage
• (Plankton, ????)
• Water repellant
• (birds and plants)

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Phospholipids
2 Classes of phospholipids (PL) (i)
glycerolphospholipids glycerol backbone
(ii) sphingomyelin spingosine
backbone Glycerolphospholipids - essential for
membrane structure - most abundant membrane
lipids Sphingolipids - Component of a
certain membrane - Sphingosine, fatty
acid and glycoside
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L-Glycerol-3-phosphate, the backbone of
phospholipids
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Examples of Phosphatides
Lecture 15. Lipids
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O
C
O
H
2
Phosphatidylcholine
O
CH
O
CH
O
3
Fatty acid moiety
)
C
(CH
N
H
CH
O
P
O
2
2
3
2
CH
O
3
Fatty acid moiety
Phosphatidylethanolamine
(CH
)
H
N
2
2
3
Phosphatidylserine
COO
CH
O
H
C
3
NH
3
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Sphingolipids
Lecture 15. Lipids
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• Sphingosine forms the backbone of sphingolipids
  (rather than glycerol)
• Sphingosines are important components of
  biological membranes
• Ceramide sphingosine fatty acid (via an amide
  linkage)
• Sphingomyelins ceramide phospholipids (via
  1-hydroxyl group)
• Glycosphingolipids ceramide b-linked sugar
  at the 1-hydroxyl moiety.

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Sphingolipids
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Examples of Sphingolipids
Lecture 15. Lipids
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Ceramide
Sphingosine
C
O
H
3
H
O
P
O
O
CH
CH
N
CH
OH
H
OH
2
H
OH
OH
H
2
2
3
H
H
O
CH
C
OH
C
C
CH
H
3
C
CH
2
2
C
C
CH
H
NH
H
2
NH
3
H
H
NH
Cholin
H
O
H
Sphingomyelin
O
R-COOH
R
fatty acid
R
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Similarities between phosphatidylcholine
and sphingomelin
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Terpenes
Lecture 15. Lipids
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• Terpenes are a class of lipids from two or more
  molecules of 2-methyl-1,2-butadiene, or isoprene
• Example of a terpene molecule
• All sterols (including cholesterol) and steroid
  hormones are terpene-based molecules

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Cholesterol

• Steroids
• (i) cholesterol and sterols of plants and fungi
• (ii) steroid hormones
• (iii) bile salts
• Roles of cholesterol in mammals
• (i) structural component of plasma membrane and
• modulates membrane fluidity
• (ii) precursor of steroid hormones and
  bile acids
• Rarely found in plants, never in bacteria

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Steroids
Lecture 15. Lipids
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• Based on a core structure consisting of three
  6-membered rings and one 5-membered ring, all
  fused together
• Cholesterol is the most common steroid in animals
  and precursor for all other steroids in animals
• Steroid hormones serve many functions in animals
  - including salt balance, metabolic function and
  sexual function

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Steroid Examples
Lecture 15. Lipids
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OH
C
D
H
C
3
C
D
CH
CH
3
A
B
CH
A
B
2
O
CH
2
testosterone
CH
Cyclopentanoperhydrophenanthrene
synthesized in five
2
steps from cholesterol
CH
CH
3
CH
2
OH
C
D
H
C
3
C
D
A
B
A
B
HO
HO
Cholesterol
Estradiol
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Cholesterol
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Steroid hormones carry messages between tissues

• Derivates of sterols
• Sex hormones and
• hormones from adrenal
• cortex
• Play important roles
• in gene expression
• Prednisolone and
• prednisone are steroid
• drug with potent
• antiinflammatory
• activities.