LIPIDS
Biology made easy with Abeeha
L I P ID S
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 Crucial Difference: Unlike carbohydrates, proteins, and nucleic
acids, lipids are not true polymers because they are not built
from repeating monomer units.
C O M P O SI T I O N
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 They contain much lower proportions of Oxygen compared to
carbohydrates.
 Some complex types also contain Phosphorus (P) and Nitrogen (N).
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C L A S S I F I C AT I O N O F L I P I D S
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FAT S
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 Glycerol: A three-carbon alcohol, each carbon bearing a hydroxyl group
(OH).
 Fatty Acid: A long carbon skeleton (usually 16–18 carbons) with a carboxyl
group (COOH) at one end.
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T Y P E OF FAT S
Saturated Fatty Acids:
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No double bonds between carbon atoms.
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The chain is "saturated" with the maximum possible number of hydrogen atoms.
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Straight structure allows close packing; solid at room temperature (e.g., animal fats).
Unsaturated Fatty Acids:
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Have one or more cis double bonds.
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Nearly all double bonds in naturally occurring fatty acids are cis, which creates a kink
(bend) in the hydrocarbon chain.
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Kinks prevent close packing; liquid at room temperature (e.g., plant/fish oils)
B I O L O G I C A L F U N C T I O N S O F F AT S
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 Adipose Tissue: Specialized mammal cells that expand and
shrink to store fat.
 Insulation: Thick subcutaneous fat layers protect the body
against heat loss.
 Organ Protection: Cushions vital organs such as kidneys and
the heart.
PHOSPHOLIPIDS
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 Phosphate Group: Carries a negative electrical charge;
often linked to a charged choline group.
 Amphipathic Nature: Possesses both a hydrophilic head and
two hydrophobic tails.
 Dual Behavior: Ambivalent relationship with water drives
cellular boundary formation.
P HO S P HO L IP ID B IL AY E R
B E HAVI O R
 Self-Assembly: Spontaneously forms double-layered sheets
when added to water.
 Shielding Effect: Hydrophobic tails point inward, away from
the aqueous environment.
 Surface Exposure: Hydrophilic heads face the external water
and internal cytosol.
 Function: Creates the foundational selectively permeable
barrier of all cells.
S T ER O ID S
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 Solubility: Classified as lipids solely due to their
hydrophobic nature.
 Examples: Cholesterol
C H O L ES T ER O L
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 Starting Material: Used to make steroid hormones, vitamin
D, and bile acids.
 Mainly produced by the liver; also obtained from food.
 Health: Too much cholesterol in the blood can contribute to
plaque buildup in arteries (atherosclerosis)
Feature
Carbohydrates
Structure
Can form long chains of
sugar units
Not true polymers
Building Blocks
Monosaccharides (e.g.,
glucose)
Glycerol + fatty acids (for
fats)
Linkage
Glycosidic bond
Ester bond
Water
Usually more hydrophilic
Mostly hydrophobic
Energy
Quick/short-term energy
Long-term energy
storage
Structural Role
Cellulose → plant cell
walls
Phospholipids → cell
membranes
Lipids