lipids. long-term energy storage do not consist of polymers insoluble in polar substances structural...
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Lipids
Lipids
• long-term energy storage
• do not consist of polymers
• insoluble in polar substances
• structural components of cells –
ex. phospholipids are the major building block in cell membranes
• "messengers" (hormones)
Lipid Construction
• Lipids are composed of three fatty acids covalently bonded to a 3-carbon glycerol
• The fatty acids are composed of CH2 units, and are hydrophobic/not water soluble
Fats• Fats
– Are constructed from two types of smaller molecules, a single glycerol and usually three fatty acids
(b) Fat molecule (triacylglycerol)
H HH H
HHH
HH
HH
HH
HH
HOH O HC
C
C
H
H OH
OH
H
HH
HH
HH
HH
HH
HH
HH
H
HCCC
CC
CC
CC
CC
CC
CC C
Glycerol
Fatty acid(palmitic acid)
H
H
H
H
HH
HH
HH
HH
HH
HH
HH
HH
HHHH
HHHHHHHHHHHH
H
HH
H HH
H HH
HH
HH
HH
HH
HHHHHHHHHHH
HH
H
H H H H H H H H HH
HH H H H
H
HH
HHHHHH
HHHHH
HH
HO
O
O
O
OC
C
C C C C C C C C C C C C C C C C C
C
CCCCCCC
CCCCCCCCC
C C C C C C C C C C C CC
CC
O
O
(a) Dehydration reaction in the synthesis of a fatEster linkage
Figure 5.11
• Saturated fatty acids– Have the maximum number of hydrogen
atoms possible– Have no double bonds
(a) Saturated fat and fatty acid
Stearic acid
Figure 5.12
Saturated Fats
• Unsaturated fatty acids– Have one or more double bonds
(b) Unsaturated fat and fatty acidcis double bondcauses bending
Oleic acid
Figure 5.12
Unsaturated Fat
• Saturated refers to the "saturation" of the molecule by hydrogen atoms
• The presence of a double C=C covalent bond reduces the number of hydrogens that can bond to the carbon chain, hence the application of the term "unsaturated“.
• Fatty acids can be saturated (meaning they have as many hydrogens bonded to their carbons as possible) or unsaturated (with one or more double bonds connecting their carbons, hence fewer hydrogens).
• Fat - solid at room temperature (saturated)• Oil - liquid (unsaturated)
Phospholipids
• Phospholipids– Have only two fatty acids– Have a phosphate group instead of a third
fatty acid
• Phospholipid structure– Consists of a hydrophilic “head” and
hydrophobic “tails”
CH2
O
PO O
O
CH2CHCH2
OO
C O C O
Phosphate
Glycerol
(a) Structural formula (b) Space-filling model
Fatty acids
(c) Phospholipid symbol
Hy
dro
ph
ob
ic t
ail
s
Hydrophilichead
Hydrophobictails
–
Hy
dro
ph
ilic
he
ad CH2 Choline
+
Figure 5.13
N(CH3)3
• The structure of phospholipids– Results in a bilayer arrangement found in cell
membranes
Hydrophilichead
WATER
WATER
Hydrophobictail
Figure 5.14
Cholesterol and steroids
• Steroids - lipids characterized by a carbon skeleton consisting of four fused rings
HO
CH3
CH3
H3C CH3
CH3
Figure 5.15
• One steroid, cholesterol– Is found in cell membranes– Is a precursor for some hormones
HO
CH3
CH3
H3C CH3
CH3
Figure 5.15
Cholesterol
• Excess cholesterol in the blood has been linked to atherosclerosis, hardening of the arteries.
Functions of Fats and Oils
• Long term energy storage • Animals convert excess sugars (beyond
their glycogen storage capacities) into fats • Plants store excess sugars as starch,
although some seeds and fruits have energy stored as oils - corn oil, peanut oil, palm oil, canola oil, and sunflower oil
• Fats store six times as much energy as glycogen.
• Insulation - heat retention• Cushion – protection (body organs, fetus)• Structural components of cells - Phospholipids
and glycolipids – cell membranes• Phospholipids are modified so that a
phosphate group (PO4-) is added to one of the fatty acids.
• The addition of this group makes a polar "head" and two nonpolar "tails".
• Waxes – cuticle -waxy layer covering the leaves and stems of many land plants; and protective coverings on skin and fur of animals
• Hormones – body regulation