Lipids are:water-insoluble organic substances but
readily soluble in organic solutions e.g. ether
The term ‘lipid’ defines compounds:
not on the basis of structural similarity
BUT in terms of their
solubility
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Water is so attracted to other water molecules that anything between them
is squeezed out of the way.
Lipids do not form polymers. Why?
Not made of monomers.
Lipids are:structurally functionally
DIVERSE
Types of Lipid
1. Triglycerides [Fats & Oils]2. Waxes3. Phospholipids4. Steroids5. Glycolipids6. Lipoproteins7. Terpenes
Types of Lipid
1. Triglycerides [Fats & Oils]
2. Waxes3. Phospholipids4. Steroids5. Glycolipids6. Lipoproteins7. Terpenes
1. Fats & Oils [Triglycerides]
•the commonest lipids in nature
•the constituents of triglycerides are:-
fatty acids (alkanoic acids)
glycerol (propane 1-2-3 triol)
1) Fatty acids- general formula: R.COOH
- most have an even number of C: most commonly 16-18
C16H32O2
R
- fatty acids may be: saturated or unsaturated
Saturated fatty acid[Single bonds only]
Unsaturated fatty acid[Double bonds]
Saturated fatty acids
Unsaturated fatty acid
The more double bonds present, the more bent the molecule is
Difference between a fat and an oil:
fats - solid at 20C oils - liquid at 20C
Why are fats solid and oils liquid at room temperature?
Molecule has kinks, keeping the fatty acids apart and as a result, oil is liquid at room
temperature.
A glyceride forms when an –OH in glycerol is replaced by an organic acid
Fatty acid
glycerol
Types of glycerides:Monoglyceride
Diglyceride
Triglyceride
Why are fats and oils classified as triglycerides?
Triglycerides:- are non-polar - float on water
Polar head - Hydrophilic
Non-polar tail - Hydrophobic
Animal fat solidifies at a low temperature
Why do plants and poikilotherms tend to have a high proportion of
unsaturated fatty acids?
To prevent their triglycerides from solidifying.
Fatty acids link to glycerol as a water molecule is lost
Fats & oils are made of one glycerol and three fatty acids
Formation of a triglyceride
formed by esterification / condensation
Fatty acids may be
different in a
triglyceride
Functions of Triglycerides1. Store energy in animals +
Yield energy
Comparison of energy yield from:
Triglycerides: 37 kJ g-1
Carbohydrates: 17 kJ g-1
MORE energy from triglycerides:
Due to more hydrogen.
2. Animals store extra fat when hibernating: acts as an insulator.
Subcutaneous fat
2. Fat around organs: protect against bumps keeps them warm
Kidney surrounded by fat
3. Brown adipose tissue (brown fat) - releases heat but no ATP- heat maintains core temperature in:
small mammals in newborn humans, particularly during cold
exposure without shivering
4. In aquatic mammals blubber contributes to buoyancy.
What is present in the hump? Why?
When fat is metabolised, it yields: 1. energy 2. more than 1 g of water for each 1 g of
fat by respiration.
FAT
5. Water is produced when fats are oxidised - this metabolic water is important in desert animals.
A kangaroo rat never drinks. Mention TWO ways
how it can get water.1. Eating2. Metabolism
6. Nerves are covered with a myelin sheath for insulation of the fibre and for fast conduction of impulses.
Test for Triglycerides
Paper becomes translucent.
Test for Triglycerides
Emulsion Test
Types of Lipid
1. Triglycerides [Fats & Oils]
2.Waxes3. Phospholipids4. Steroids5. Glycolipids6. Lipoproteins7. Terpenes
Waxes: not a food source no enzymes to break them down
Structure of Waxes
one fatty acid an alcohol of high molecular weight instead of glycerol
Feathers do not get wet.
WHY?
Raindrops on feathers.
Waxes are mainly for e.g.
cutin makes up the waxy cuticle of leaves
fruits produce a waxy coating to
keep from drying out
Sebum in mammalian skin
Wax in ears traps:dustsandother foreign
particles
do not go deeper into the ear and cause no damage
Suberin in Casparian strips,
Exoskeleton in
insects
[contains wax]
Waxes build elaborate structures such as beehives
Types of Lipid1. Triglycerides [Fats & Oils]2. Waxes
3.Phospholipids4. Steroids5. Glycolipids6. Lipoproteins7. Terpenes
Phospholipidslipids with a
phosphate group condensationH2O
Phospholipids are made of one phosphate group and 2 fatty acids
Phospholipids are amphipathic – have both polar & nonpolar portions
Phospholipids are constituents of membranes
Two structures formed by self-assembly of phospholipids in aqueous environments
Types of Lipid1. Triglycerides [Fats & Oils]2. Waxes3. Phospholipids
4.Steroids5. Glycolipids6. Lipoproteins7. Terpenes
Steroids are structurally different from all other
lipids
consist of a complex carbon ring structure
Cholesterol is a steroid.
Cholesterol:• is the steroid present in the
largest amount in humans
• a key intermediate in the synthesis of related steroids
• an important constituent of animal plasma membranes
made in the liver
Sex hormones are Steroids
Types of Lipid
1. Triglycerides [Fats & Oils]2. Waxes3. Phospholipids4. Steroids
5.Glycolipids6. Lipoproteins7. Terpenes
Glycolipids• carbohydrate + lipid • components of cell membranes
Types of Lipid1. Triglycerides [Fats & Oils]2. Waxes3. Phospholipids4. Steroids5. Glycolipids
6.Lipoproteins7. Terpenes
Lipoproteins• occur in membranes • are the form in which
lipids are transported in the blood e.g. fatty acids are bound to albumin
protein
triglyceride &
cholesterol
phospholipid
Lipoproteins vary in size and composition
Types of Lipid
1. Triglycerides [Fats & Oils]2. Waxes3. Phospholipids4. Steroids5. Glycolipids6. Lipoproteins
7.Terpenes
Terpenes may be:volatile : attract pollinators
less volatile:strongly bitter-tasting to prevent plants being eaten by herbivores
Examples of terpenes:
light-absorbing pigments in animals & plants
carotenoidsrubber
β carotene:- traps light in plants and in humans- is broken down into two vitamin A
molecules from which we make rhodopsin
Carotenoids also act as antioxidants:
trap free radicals and
inhibit oxidation
What are free radicals?
free radicals attack healthy cells through a damaging chain reaction of
oxidation [free radicals steal electrons]
An atom or group of atoms that has at least one unpaired electron and is therefore unstable and
highly reactive
Antioxidants neutralise the free radicals
Antioxidants: prevent cancer improve the
immune system
electron
Antioxidant
Free radical
Question: [MAY, 2007]
Suggest explanations for the following statement.Fats are used as storage molecules rather than as an immediate energy source. (2)Fats are ideal for storing energy as they release large quantities of energy. This means that small quantities of stored fat carried by the organism provide sufficient energy without having to carry a heavy load. Fat molecules are large and would take a long time to release energy, making them unsuitable for immediate sources of energy.
Question: [SEP, 2007]
Use your knowledge of biology to explain the following. (5 marks)
Most animals use fats, rather than starch, as energy-storage molecules.
No life as we know it can exist without lipids. Comment on the importance of lipids to life.
[1994]
Give an account of the important roles played by lipids in living organisms. [SEP, 1998]
Give an overview of the importance of lipids for living organisms. [SEP, 2009]
Essay Titles