1. Lipids
HL Biology
Cells & Biomolecules

2. Homework review
• Are fats part of a healthy diet??

3. Lipids
• A group of compounds that mix poorly with
water.
• Varied in form of function
• Three main types:
– Triglycerides (fats)
– Phospholipids
– Steroids
This lesson will focus on Triglycerides (fats)

4. Triglycerides (fats)
• Triglycerides are made from two kinds of
smaller molecules:
• One glycerol and three fatty acids.
• Formed by condensation reactions

5. Fatty Acids
• There are two parts to a fatty acid:
– A carboxyl group (COOH)
– An unbranched hydrocarbon chain.
Fatty acids can be saturated, monounsaturated and
polyunsaturated.

6. Spot the difference?

7. Types of Fatty Acids
• Saturated = all of the carbon atoms in the
chain are connected by single covalent bond,
meaning there is no more room for Hydrogen
atoms (It is saturated with hydrogen!)
• Monounsaturated = only one double bond
• Polyunsaturated = two or more double bonds

9. Saturated Fats
• A fat made from saturated fatty acids is called
a saturated fat
• Most animal fats are saturated
• The lack of double bonds and their flexibility
allow the fat molecules to pack together
tightly, forming solids at room temperature.
• Eg. Lard or butter

11. Unsaturated fats
• The fats of plants and fish are normally
unsaturated
• They are usually liquid at room temperature
and referred to as oils,
• Eg. Olive oil, fish oil
• Nearly all natural occurring unsaturated fats
have Cis double bonds.

12. Cis or Trans Unsaturated Fats
• Double bonds can be cis or trans bonds.
• Cis bonds – all hydrogen atoms are bonded to
carbon atoms on the same side. Results in a
“bent” structure.
• Trans bonds – hydrogen atoms are bonded to
carbon atoms on opposite sides of a double
bond. Results in a “straight” structure.

13. Spot the difference?
How do you think this affects the melting point of the fat?

14. Cis or Trans
• The kinks where the cis double bonds are
located prevent the molecules from packing
together closely enough to solidify at room
temperature.
• This is why most natural unsaturated fats are
liquid at room temperature (oils)

16. Trans fats
• Unsaturated fats can be synthetically
converted to trans fats to make them a solid at
room temperature.
• Eg, margarine and peanut butter.
• Trans-fats are normally found in heavily
processed food.
What are the effects of trans-fats in diet?

17. Lipids for Energy storage

18. Lipids for Energy Storage
• Lipids are better for long-term energy storage
compared to carbohydrates.
• Lipids store twice as much as carbohydrates
energy per gram.
• Glycogen is stored with water, making it even
heavier.
• Lipids can store 6 times more energy per gram
than carbohydrates.