LIPIDS
● Include fats (triglycerides), phospholipids, glycolipids, sterols and others
● Insoluble in water but highly soluble in non-polar solvents
Simple Lipids
Consist of an alcohol (usually glycerol) linked to one or more fatty acids via an ester linkage
[Triglycerides]
Glycerol
● Molecular formula C3H8O3
● Soluble in water due to each carbon bearing a polar hydroxyl (OH) group
Fatty Acids
● Carboxylic acids composed of an acidic carboxyl (COOH) group at one end an attached
hydrocarbon chain
● Hydrophobic due to abundance of non-polar C-H bonds
Formation
An ester linkage is formed between a hydroxyl (OH) group of glycerol and the carboxyl (COOH) group
of a fatty acid (condensation reaction)
As each glycerol has 3 -OH groups, it can form up to 3 ester linkages
Properties
1. Melting point of fats increases with hydrocarbon chain length
● Longer hydrocarbon chains -> greater hydrophobic interactions between the chains
-> higher melting points as more energy required to break the bonds
2. Melting point of fats decreases as degree of unsaturation of fatty acid tails increases
● Kinks where double bonds are located in unsaturated fatty acids prevent the
molecules from packing closely -> weaker hydrophobic interactions -> less energy
required to break the bonds
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,Structure to function (Triglycerides)
Structure Function
● Higher proportion of C and H atoms ● Release a larger amount of energy upon
compared to O atoms oxidation
● Greater number of C atoms per unit ● More efficient energy stores than
mass that carbohydrates carbohydrates
● Highly reduced molecules ● Release more water (metabolic water)
i.e. contain two-fold more hydrogen when oxidised during cellular respiration
atoms per unit mass than compared to carbohydrates
carbohydrates ● Important to desert animals (camels)
● C-H bonds are non-polar, hence ● Osmotically inactive and do not affect
triglycerides are hydrophobic water potential of cells when stored in large
● No associated water molecules amounts
stored along with triglycerides -> no ● Keeps an animal’s body mass to a
extra weight due to water of minimum to facilitate locomotion
hydration ● Good thermal insulator (blubber)
● Hydrocarbon tails are non-polar ● Triglycerides can slide under pressure
● Weak hydrophobic interactions ● Adipose tissue around vital organs helps
between triglyceride molecules cushion and protect vital organs against
physical impacts
● Lower molecular weight than water ● Less dense than water
per unit volume ● Aids buoyancy of aquatic animals (blubber)
Complex lipids
Esters of fatty acid(s) and an alcohol plus other chemical groups (e.g. phosphate and sugar)
[Phospholipids]
● Consist of one glycerol and two fatty acids, with the third -OH group of glycerol joined to a
negatively-charged phosphate group
● Additional small molecules, usually charged or polar (e.g. serine, choline, inositol) can be
linked to the phosphate group to form various phospholipids
Formation
● Two fatty acids are linked to glycerol by an ester linkage
● Phosphate group linked to third -OH group of glycerol by a phosphoester linkage
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, Properties
● The two fatty acids that comprise the hydrocarbon tails are non-polar and hence
hydrophobic
● The phosphate group and its attachments form a polar/charged hydrophilic head
● Thus phospholipids are amphipathic/amphiphilic
● Three types of lipid aggregates form when phospholipids are placed in aqueous
environments -> serve to shield hydrophobic tails from aqueous environment
1) Micelle (Phospholipid monolayer)
2) Bilayer
3) Liposome/vesicle (lipid bilayer folds back on itself)
Structure to function (Phospholipids)
Structure Function
Phospholipids are amphipathic ● Form a bilayer in s electively permeable cell
molecules, each with 2 non-polar, membrane -> hydrophilic heads exposed to
hydrophobic fatty acids tails and a aqueous medium, hydrophobic tails excluded from
charged, hydrophilic phosphate head aqueous medium in the non-polar interior of the
bilayer -> forms an effective barrier between cell
and external environment to maintain a constant
Copyright © 2019 tonyndr
● Include fats (triglycerides), phospholipids, glycolipids, sterols and others
● Insoluble in water but highly soluble in non-polar solvents
Simple Lipids
Consist of an alcohol (usually glycerol) linked to one or more fatty acids via an ester linkage
[Triglycerides]
Glycerol
● Molecular formula C3H8O3
● Soluble in water due to each carbon bearing a polar hydroxyl (OH) group
Fatty Acids
● Carboxylic acids composed of an acidic carboxyl (COOH) group at one end an attached
hydrocarbon chain
● Hydrophobic due to abundance of non-polar C-H bonds
Formation
An ester linkage is formed between a hydroxyl (OH) group of glycerol and the carboxyl (COOH) group
of a fatty acid (condensation reaction)
As each glycerol has 3 -OH groups, it can form up to 3 ester linkages
Properties
1. Melting point of fats increases with hydrocarbon chain length
● Longer hydrocarbon chains -> greater hydrophobic interactions between the chains
-> higher melting points as more energy required to break the bonds
2. Melting point of fats decreases as degree of unsaturation of fatty acid tails increases
● Kinks where double bonds are located in unsaturated fatty acids prevent the
molecules from packing closely -> weaker hydrophobic interactions -> less energy
required to break the bonds
Copyright © 2019 tonyndr
,Structure to function (Triglycerides)
Structure Function
● Higher proportion of C and H atoms ● Release a larger amount of energy upon
compared to O atoms oxidation
● Greater number of C atoms per unit ● More efficient energy stores than
mass that carbohydrates carbohydrates
● Highly reduced molecules ● Release more water (metabolic water)
i.e. contain two-fold more hydrogen when oxidised during cellular respiration
atoms per unit mass than compared to carbohydrates
carbohydrates ● Important to desert animals (camels)
● C-H bonds are non-polar, hence ● Osmotically inactive and do not affect
triglycerides are hydrophobic water potential of cells when stored in large
● No associated water molecules amounts
stored along with triglycerides -> no ● Keeps an animal’s body mass to a
extra weight due to water of minimum to facilitate locomotion
hydration ● Good thermal insulator (blubber)
● Hydrocarbon tails are non-polar ● Triglycerides can slide under pressure
● Weak hydrophobic interactions ● Adipose tissue around vital organs helps
between triglyceride molecules cushion and protect vital organs against
physical impacts
● Lower molecular weight than water ● Less dense than water
per unit volume ● Aids buoyancy of aquatic animals (blubber)
Complex lipids
Esters of fatty acid(s) and an alcohol plus other chemical groups (e.g. phosphate and sugar)
[Phospholipids]
● Consist of one glycerol and two fatty acids, with the third -OH group of glycerol joined to a
negatively-charged phosphate group
● Additional small molecules, usually charged or polar (e.g. serine, choline, inositol) can be
linked to the phosphate group to form various phospholipids
Formation
● Two fatty acids are linked to glycerol by an ester linkage
● Phosphate group linked to third -OH group of glycerol by a phosphoester linkage
Copyright © 2019 tonyndr
, Properties
● The two fatty acids that comprise the hydrocarbon tails are non-polar and hence
hydrophobic
● The phosphate group and its attachments form a polar/charged hydrophilic head
● Thus phospholipids are amphipathic/amphiphilic
● Three types of lipid aggregates form when phospholipids are placed in aqueous
environments -> serve to shield hydrophobic tails from aqueous environment
1) Micelle (Phospholipid monolayer)
2) Bilayer
3) Liposome/vesicle (lipid bilayer folds back on itself)
Structure to function (Phospholipids)
Structure Function
Phospholipids are amphipathic ● Form a bilayer in s electively permeable cell
molecules, each with 2 non-polar, membrane -> hydrophilic heads exposed to
hydrophobic fatty acids tails and a aqueous medium, hydrophobic tails excluded from
charged, hydrophilic phosphate head aqueous medium in the non-polar interior of the
bilayer -> forms an effective barrier between cell
and external environment to maintain a constant
Copyright © 2019 tonyndr
