1. Lipids
AP Biology

2. Lipids

3. Lipids Lipids are composed of C, H, O Major Types of Lipids
long hydrocarbon chains (H-C)
Major Types of Lipids
Fats and oils
phospholipids
Steroids
Waxes
Made of same elements as carbohydrates but very different structure/ proportions & therefore very different biological properties

4. Functions of Lipids Energy Storage Cushion body organs Insulation
Think blubber
Waterproofing
Think duck feathers
Cell-to-cell communication
Think hormones
Formation of cell membranes

5. Basic Structure of Lipids
Do not form “polymers” exactly
Not big molecules made of smaller subunits
not a “choo-choo train” of monomers
Mostly long chains of carbon and hydrogen atoms stuck to a “hook”….
Glycerol =
the hook

6. dehydration synthesis
Fats and oils
Structure:
glycerol (3C alcohol) + fatty acid
fatty acid = long HC “tail” with carboxyl (COOH) group “head”
enzyme
Look at structure… What makes them hydrophobic?
Note functional group = carboxyl
H2O
dehydration synthesis

7. Building Fats Triglyceride 3 fatty acids linked to glycerol
ester linkage = between OH & COOH
hydroxyl
carboxyl
Yet
Another
type of
Covalent
bond
BIG FAT molecule!!

8. Dehydration synthesis
H2O
dehydration synthesis
enzyme
H2O
Pulling the water out to free up the bond
enzyme
H2O
enzyme
H2O

9. Why do humans like fatty foods? very evenly – no polarity
Fats store energy
Long HC chain
polar or non-polar?
hydrophilic or hydrophobic?
Function:
energy storage
concentrated
all C-H Bonds
2x energy of
carbohydrates
C and H share electrons
very evenly – no polarity
results.
What happens when you add oil to water
Why is there a lot of energy stored in fats?
• big molecule
• lots of bonds of stored energy
So why are we attracted to eating fat?
Think about our ancestors on the Serengeti Plain & during the Ice Age. Was eating fat an advantage?

10. Why is Fat the preferred energy storage molecule of animals
Why is Fat the preferred energy storage molecule of animals? (as opposed to starch)
More C-H Bonds than in carbs…Remember the Glucose molecule:

11. C O C C C C 5' 4' 1' 3' 2' CH2OH 6' H OH H OH H H OH H OH Where’s the
energy?
CH2OH 6' C O
In the C-H BONDS!! 5' H OH H C C 4' 1' OH H H OH C C 3' 2' H OH

12. In lipids there are even MORE C-H bonds than in carbs!
Thus, more energy packed in a lipid per unit mass
TWICE as much as in a carbohydrate!
ALL ENERGY!!!

13. Saturated vs. Unsaturated Fats
Remember that covalent bonds can be
Single, double, or triple
In Fatty acids, generally the covalent bonds between the carbons are SINGLE
However, sometimes a DOUBLE bond can exist between carbons
This means the carbons involved in the double bond are “holding hands” with each other and NOT “holding hands” wi
A DOUBLE bond can cause BENDING in the carbon chain.

14. Saturated fats
This means that all the carbons are SATURATED with hydrogens!
This means each carbon is holding as many hydrogens as it possibly can (2 H’s per C)
No C=C double bonds
This results in long, straight chains
These can pack TIGHTLY together
solid at room temp.
ANIMAL fats, typically
Butter, lard
Mostly animal fats

15. Unsaturated fats C=C double bonds in the fatty acids
Called UNsaturated because the carbons are NOT holding hands with as many hydrogens as possible
C=C double bonds cause the fatty acid to bend
liquid at room temperature
the kinks made by double bonded C prevent the molecules from packing tightly together
plant & fish fats
vegetable oils
Mostly plant lipids
Think about “natural” peanut butter:
Lots of unsaturated fats Oil separates out
Companies want to make their product easier to use:
Stop the oil from separating Keep oil solid at room temp.
Hydrogenate it = chemically alter to saturate it
Affect nutrition?
mono-unsaturated?
poly-unsaturated?

16. Saturated vs. unsaturated

17. It’s just like a penguin…
Phosphate
Phospholipids
Often drawn
Like this
Structure:
glycerol + 2 fatty acids + PO4
PO4 = Phosphate group
PO4 = negatively charged
Fatty Acids
It’s just like a penguin…
A head at one end
& a tail at the other!

18. Phospholipids Hydrophobic or hydrophilic? fatty acid tails =
PO4 head =
split “personality”
hydrophobic
NONPOLAR
hydrophillic
POLAR
“attracted to water”
Come here, No, go away!
interaction with H2O is complex & very important!
“repelled by water”

19. Phospholipids in water
Hydrophilic heads “attracted” to H2O
Hydrophobic tails “hide” from H2O
can self-assemble into “bubbles”
bubble = “micelle”
can also form a phospholipid bilayer
“bubbles” of phospholipids an early evolutionary step for cells?
Animation
water
bilayer
water

20. Phospholipids & cells Phospholipids of cell membrane
double layer = bilayer
hydrophilic heads on outside
in contact with aqueous solution outside of cell and inside of cell
hydrophobic tails on inside
form core
Phospholipid bilayer
Note other molecules in membrane…

21. Why is this important? Phospholipids create a barrier in water
define outside vs. inside
they make cell membranes!
Tell them about soap!

22. Steroids Structure: 4 fused C rings + ??
different steroids created by attaching different functional groups to rings
different structure creates different function
examples: cholesterol, sex hormones
cholesterol

23. Cholesterol Important cell component animal cell membranes
precursor of all other steroids
including vertebrate sex hormones
high levels in blood may contribute to cardiovascular disease

24. Cholesterol Important component of cell membrane
helps keep cell membranes fluid yet firm

25. From Cholesterol  Sex Hormones
What a big difference a few atoms can make!
Same C skeleton, different functional groups

26. Any Questions?