LIPIDS
2.3 Carbohydrates and Lipids
LIPIDS
• Lipids are a diverse group of molecules made of carbon, hydrogen and oxygen atoms.
• This category of molecules includes:
-fats (triglycerides)
-phospholipids
-steroids
-waxes
• All lipids have a common characteristic: they are all hydrophobic / insoluble in water
• Consist mostly of C-H atoms in a non-polar bond arrangement
Structure and Formation of a Triglyceride (FAT)
• A triglyceride is made of a glycerol molecule and 3 fatty acids that come together in a condensation reaction
• Glyercol is a kind of alcohol
• Fatty acids are long chains of hydrocarbons with a carboxyl group at one end of the chain.
Saturated vs Unsaturated Fats
• The difference between a saturated fat and an unsaturated fat is in the fatty acid chains.
Saturated fat:
- there are only single bonds between the carbons in the fatty acid chains.
- As a result, the carbons are “saturated” or completely surrounded by hydrogens and are bonded to 4 other elements.
- Saturated fats take up less space and therefore are more dense.
- They tend to be solid at room temperature
- Ex: animal fats (such as in meat), butter
Unsaturated fat:
- There is at least 1 double bond between two carbons in a fatty acid chain.
- As a result, the carbons are “unsaturated” – they are NOT completely surrounded by hydrogens and are bonded to less than 4 other elements.
- This produces a “kink” or bend in the molecule which causes the molecule to take up more space, making it less dense.
- As a result, they tend to be liquid at room temperature.
- Ex: vegetable oils, fish oils
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Monounsaturated Fatty Acids
- have 1 double bond in the fatty acid chain
- Ex: oleic acid found in animal fats and vegetable oils (such as olive oil)
Polyunsaturated Fatty Acids
- have more than 1 double bond in the fatty acid chain.
- These include essential fatty acids (not produced by body and must be obtained through one’s diet)
- Ex: linoleic acid which is found in vegetable oils.
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Cis and Trans Fatty Acids
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Cis-fatty acids
- When the hydrogens are found on the same side of a double bond
- In organisms, almost always found in this form
- This structure makes it harder to pack the molecules together
- As a result, they have lower melting points and usually liquids at room temperature (oils).
Trans-fatty acids
- When the hydrogens are found on opposite sides of a double bond.
- They have high melting temperatures are solid at room temperature
- They are made artificially by partial hydrogenation of vegetable or fish oils
- This is done to produce solid fats for use in margarine and other processed foods.
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Functions of Lipids:
a) store a large amount of energy
- Excellent long-term energy storage.
o 1 g of fat contains more than twice as much energy as 1 g of carbohydrate (9 kcal/g in lipids vs. 4 kcal/g in carbs)
- Humans store fat in adipose tissue, located immediately beneath the skin and around organs (such as the kidney)
b) phospholipids are the structural component of membranes
- Phospholipids have a similar structure as triglycerides, except one of the fatty acid is replaced with a phosphate group
- Therefore, they contain 1 phosphate group, 1 glycerol, 2 fatty acids
c) Steroids
o Built by a carbon skeleton consisting of four fused hydrocarbon rings
o Cholesterol is one type of steroid
o Cholesterol is also the building block of testosterone and estrogen (hormones that control development of sexual characteristics)
o Cholesterol is important in maintaining the fluidity of cellular membranes but too much can cause heart problems
Remember lipoproteins?
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Lipoproteins are groups of molecules with a single layer of phospholipids on the outside and the fat molecules in the inside. They transport triglycerides and cholesterol in the blood stream.
High Density Lipoproteins (HDL) vs Low Density Lipoproteins (LDL)
|HDL |LDL |
|“good cholesterol” |“bad cholesterol” |
|Remove fat and cholesterol from cells and blood vessels to be |Transport fats to artery walls and can lead to atherosclerosis |
|excreted or reutilized by the liver |(the hardening of blood vessels) |
d) waxes provide protective coating for plants to prevent water loss
e) insulators for animals (keeps animals warm by preventing
- adipose tissue surrounding kidneys and other organs also act as shock absorbers
f) facilitate the digestion & metabolism of other nutrients
g) help the absorption and transport of vitamins A,D,E,& K
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