What characteristics define a lipid?
Molecules whose main structure is built from carbon atoms
Why are lipids hydrophobic and nonpolar?
a lipid is basically long chains of C-C and C-H bonds
Carbon and hydrogen have very similar electronegativity. They share electrons almost equally.
If it had Oxygen and Hydrogen, the water would only mix with partial charges
Why are lipids NOT polymers?
lipids don’t have repeating monomers like other macromolecules
lipids form a fixed structure
they are made by joining a few different components together, usually glycerol backbone and fatty acids
What is a hydrocarbon?
Hydrocarbons are molecules that contain only carbon and hydrogen.
they are hydrophobic bc electrons are shared equally in C-H bonds
How do C–H bonds affect polarity?
generally polarity depends on electronegativity (how strong atoms pull electrons)
C-H and C-C share electrons almost equally, There is no partial positive or negative poles form
Why are lipids important in the plasma membrane?
Lipids are basically the main material the plasma membrane is built from.
Without them, a cell couldn’t separate its inside from the outside
they form the membrane barrier:
Phospholipids have two opposite properties:
hydrophilic head → likes water
hydrophobic tails → avoid wate
What is a fatty acid?
A fatty acid is a hydrocarbon chain bonded to a
carboxyl (–COOH) functional group
contain 14-20 carbon atoms
can be saturated or unsaturated
What functional group is attached to fatty acids?
the carboxyl group
It’s basically the reactive “attachment point” that lets fatty acids connect to other molecules.
It forms the lipid molecule. Without the carboxyl group, triglycerides and phospholipids could not form.
What are isoprenes?
What are isoprenoids and how do they differ from fatty acids?
What is a saturated fatty acid?
Saturated hydrocarbon chains consist of only single bonds between the carbons
Why do saturated fats contain maximum hydrogen atoms?
Saturated fats contain the maximum number of hydrogen atoms because all carbon atoms are connected by single bonds, allowing each carbon to bond with as many hydrogen atoms as possible.
What is an unsaturated fatty acid?
Unsaturated hydrocarbon chains have one or more double bonds in the hydrocarbon chains
Hydrogen atoms are removed to make a double bond. Forms a kink in the chain
How do double bonds change fatty acid shape?
Double bonds introduce a fixed bend in fatty acid chains because the C=C bond prevents rotation, creating a kink that disrupts tight packing of the molecules.
What is polyunsaturation?
Polyunsaturation means a fatty acid contains two or more carbon–carbon double bonds (C=C) in its hydrocarbon chain
Why are natural unsaturated fats usually in the cis form?
At a C=C double bond the groups can be arranged two ways:
cis → hydrogens on the same side → bent chain
trans → hydrogens opposite → straight chain
Unsaturated hydrocarbon chains are cis because cellular desaturase enzymes insert double bonds in a fixed orientation that places hydrogens on the same side, producing bends that maintain membrane fluidity.
Why are saturated fats solid at room temperature?
Saturated fats are solid at room temperature because their straight fatty acid chains pack tightly together.(waxes)
Highly saturated lipids, such as butter, are solid at room
temperature
Why are unsaturated fats liquid?
Unsaturated fats are liquid because double bonds create bends that prevent the molecules from packing tightly together.
Because the chains are bent:
they cannot stack closely
less surface contact
weaker van der Waals forces
How does chain length affect fluidity?
The longer the fatty acid tail is, the more it can stick to nearby tails.
Because it has more area touching other tails, the attraction between them becomes stronger.
When they stick strongly, they can’t move around easily → the membrane becomes less fluid (more stiff).
Long tails grab each other more → movement slows down → membrane gets rigid.
What is hydrogenation?
Hydrogenation is the chemical process of adding hydrogen (H₂) to the carbon–carbon double bonds of unsaturated fatty acids.
How are trans fats formed?
Trans fats form when unsaturated oils are partially hydrogenated, which flips the natural cis double bond into a trans double bond.
Why are polyunsaturated fats considered healthier?
Polyunsaturated fats are healthier because their bent shape keeps membranes flexible and helps control cholesterol levels
What are the three major lipid types found in cells?
Steroids: Regulate membrane fluidity and stability
They sit between phospholipids and prevent membranes from becoming too rigid or too fluid.
fats: (Triglycerides)
Energy storage molecules
Stored in lipid droplets and used as long term fuel.
Phospholipids:
Main structural component of cell membranes
They form the phospholipid bilayer that separates the inside of the cell from the outside.
What property defines lipids rather than a shared structure?
Lipids are defined by their hydrophobic, nonpolar nature and insolubility in water rather than a shared chemical structure.
