Chapter 5 Macromolecules-Lipids
Lipids • Lipids are composed of C, H, O– long hydrocarbon chains (H-C)
• “Family groups”– fats– phospholipids– steroids
• Do not form polymers– big molecules made of smaller subunits– not a continuing chain
Fats • Structure:– glycerol (3C alcohol) + fatty acid• fatty acid =
long HC “tail” with carboxyl (COOH) group “head”• 12-20 carbons- Always an even number.• These extensive chains make fats very
nonpolar.
dehydration synthesis
H2O
enzyme
Fats (Tricylglycerols)• Fats constructed of two kinds of smaller molecules– Glycerol - Three carbons covalently bound to one
another, each with a single hydroxyl group.
Function of Fats
• Energy storage. 1 gram of fat stores more than 2x the energy of 1 gram of carbohydrate.
• Insulation. Fat is an exceptional thermal and electrical insulator.
Formation of Fats
• Fats form as a result of a dehydration reaction between glycerol and a fatty acid.
• This kind of linkage is called an ester linkage.• Ester linkage = between OH & COOH
Fatty acid(palmitic acid)
(a)Dehydration reaction in the synthesis of a fatGlycerol
(b) Fat molecule (triacylglycerol)
Ester linkage
Fig. 5-11b
Dehydration synthesis
dehydration synthesis
H2O
H2O
H2O
H2O
enzyme
enzyme
enzyme
Fats store energy• Long HC chain– polar or non-polar?– hydrophilic or hydrophobic?
• Function:– energy storage • concentrated– all H-C!
• 2x carbohydrates– cushion organs– insulates body• think whale blubber!
Why do humanslike fatty foods?
Saturated v. Unsaturated Fats• Saturated fats are composed of fatty acid chains that
contain no double bonds. – Saturated with hydrogens.
• Unsaturated fats are composed of fatty acid chains with double bonds. – They are not saturated.
• Naturally occurring fatty acid chains are all cis-fats.
Saturated fats
• All C bonded to H• No C=C double bonds– long, straight chain–most animal fats – solid at room temp.• contributes to
cardiovascular disease (atherosclerosis) = plaque deposits
Unsaturated fats• C=C double bonds in
the fatty acids– plant & fish fats – vegetable oils– liquid at room temperature• the kinks made by double
bonded C prevent the molecules from packing tightly together
mono-unsaturated?poly-unsaturated?
Fig. 5-12b
(b) Unsaturated fat
Structural formulaof an unsaturatedfat molecule
Oleic acid, anunsaturatedfatty acid
cis doublebond causesbending
Fig. 5-12a
(a) Saturated fat
Structuralformula of asaturated fatmolecule
Stearic acid, asaturated fattyacid
Saturated vs. unsaturatedsaturated unsaturated
Phospholipids & cells• Phospholipids of cell membrane – double layer = bilayer– hydrophilic heads on outside
• in contact with aqueous solution outside of cell and inside of cell– hydrophobic tails on inside
• form core– forms barrier between cell &
external environment
Phospholipids • Structure:– glycerol + 2 fatty acids + PO4
• PO4 = negatively charged
It’s just like apenguin…A head at one end& a tail at the other!
Phospholipids• Hydrophobic or hydrophilic?– fatty acid tails =– PO4 head =– split “personality”
interaction with H2O is complex & very important! “repelled by water”
“attracted to water”
hydrophobichydrophillic
Fig. 5-13
(b) Space-filling model(a) (c)Structural formula Phospholipid symbol
Fatty acids
Hydrophilichead
Hydrophobictails
Choline
Phosphate
Glycerol
Hydr
opho
bic t
ails
Hydr
ophi
lic h
ead
20
Phospholipid
Phospholipids in water• Hydrophilic heads “attracted” to H2O
• Hydrophobic tails “hide” from H2O– can self-assemble into “bubbles” • bubble = “micelle”• can also form a phospholipid bilayer
bilayer
water
water
Phospholipids
• Similar to fats in structure.
• Three components– Glycerol– 2 Fatty acids– Phosphate group
• Phosphate group replaces the 3rd fatty acid in tricylglycerol
Phospholipid Properties
• Phospholipids are amphipathic.
• In an aqueous environment the hydrophobic tails of phospholipids are pushed together while the heads interact with water and each other.
• Because of this, phospholipids spontaneously take on a characteristic bilayer arrangement.
Functional Importance of Phospholipids
• Phospholipid bilayer is the primary component of biological membranes
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/lipos.gif
Importance of Phospholipids• Water and ions cannot freely diffuse through the
bilayer.
• Phospholipids keep the inside of the cell inside the cell and the outside of the cell outside the cell.
• There are proteins embedded in the phospholipid bilayer that allow select polar molecules and ions through the bilayer.
Why is this important?• Phospholipids create a barrier in water– define outside vs. inside– they make cell membranes!
Steroids
• Steroids are another class of lipids.
• They are hydrophobic and always have the same root structure.
• Functional groups attached to the steroid structure greatly influence the biological action of the steroid.
Steroids• Structure:– 4 fused C rings
• different steroids created by attaching different functional groups to rings
• different structure creates different function – examples:
• Cholesterol• Sex hormones
cholesterol
Important Steroids
http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch26/ch26-5-1.html
Cholesterol• Important cell component – animal cell membranes– precursor of all other steroids• including vertebrate sex hormones
– high levels in blood may contribute to cardiovascular disease
Cholesterol
helps keep cell membranes fluid & flexible
Important component of cell membrane
From Cholesterol Sex Hormones• What a big difference a few atoms can make!
2006-2007
Lipids!
34
Tricylglycerol
Glycerol
Fatty Acid
Triacylglycerol
35
Review
• What two components make up fats?
• What is an Ester Linkage?
• Triacylglycerol (triglyceride):
36
Saturated Fats Vs. Unsaturated Fats
• Saturated:
• Unsaturated:
37
Function and Storage of Fat
• Function:
• Storage:Adipose Tissue
38
Phospholipids
• Structure:
• How do they behave in water?
• Relation to cell membrane:
39
Steroids
• Structure:
• Ex) Cholesterol:
How are Phospholipids different than fats?
• The phosphate is charged.
• This makes that part of the molecule _________________________
• The fatty acid chains are _________________________
Function of Steroids
• Component of cell membranes (cholesterol).
• Hormones
Questions to Consider
• Steroids including cholesterol are do not usually travel alone in the bloodstream. Why not?
• Suppose a phopholipid membrane surrounded an oil droplet. It frequently does in plant seeds. What form might the membrane take on in these cases?
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