Bio Lipids

Into which three broad groups are lipids classified?

(a) Simple lipids (e.g., triglycerides) (b) Compound lipids (e.g., phospholipids, glycolipids) (c) Steroids/sterols (e.g., testosterone, cholesterol)

What monomers combine to form simple and compound lipids?

Glycerol and fatty acids

Describe the structure of glycerol.

A 3-carbon alcohol in which each carbon bears a polar hydroxyl (–OH) group

Why is glycerol soluble in water?

Its hydroxyl groups can form hydrogen bonds with water, making it polar and water-soluble

What two structural components make up a fatty acid?

A long non-polar hydrocarbon chain (tail) and a terminal carboxyl (–COOH) group

Why are lipids insoluble in water yet soluble in organic solvents?

Their non-polar C–H bonds give hydrophobic tails that do not form hydrogen bonds with water but interact with non-polar organic solvents (e.g., ethanol, chloroform)

Define a saturated fatty acid.

A fatty acid whose hydrocarbon tail contains no C=C double bonds; every carbon is fully saturated with hydrogen

Define an unsaturated fatty acid.

A fatty acid containing at least 1 C=C double bonds, making kinks in the hydrocarbon tail

How does hydrocarbon chain length affect the melting point of saturated fatty acids?

Longer chains → more hydrophobic interactions → higher melting point

How does the number of C=C double bonds affect the melting point of unsaturated fatty acids?

More double bonds (kinks) → less close packing → fewer hydrophobic interactions → lower melting point

Name the covalent bond between glycerol and a fatty acid.

Ester bond COO

How is an ester bond formed during triglyceride synthesis?

By a condensation reaction between the –OH of glycerol and the –COOH of a fatty acid, releasing one H₂O

How many water molecules are released when one triglyceride forms?

3 (1 per ester bond)

What are the components of one triglyceride molecule?

One glycerol backbone ester-linked to three fatty acids

Explain why triglycerides are a compact energy store.

Their long hydrocarbon chains contain many C–H bonds, which oxdise to produce 2x as much ATP than that of the same mass of carbohydrates

Why can triglycerides be stored in cells without affecting water potential?

They are hydrophobic and insoluble in water

Give 3 non-storage functions of triglycerides in animals.

Source of metabolic water, thermal insulation, mechanical protection (cushioning) and buoyancy

Differentiate fats and oils.

Both are triglycerides; fats are solid at room temperature (~20 °C), oils are liquid

List the reactants that form a phospholipid.

One glycerol, two fatty acids, and one phosphoric acid (phosphate group)

Which bonds link the phosphate group and glycerol in a phospholipid?

Phosphoester bond(s)

Why are phospholipids described as amphipathic?

They possess a hydrophilic, negatively charged phosphate head and two hydrophobic hydrocarbon tails

What structures can phospholipids self-assemble into in water?

Bilayers, micelles, and liposomes

How does the amphipathic nature of phospholipids enable membrane formation?

Hydrophilic heads face the aqueous exterior/interior, while hydrophobic tails face inward, producing a bilayer with a hydrophobic core that acts as a barrier

State two functions of biological membranes built from phospholipids.

(1) Separate cell contents from the external aqueous environment; (2) form organelle membranes for compartmentalisation

When fatty acid chain increases in length, melting point __ because

Melting point increases
When C-H bond increases, theres greater hydrophobic interaction between the hydrocarbon chains of the fatty acids

Why do desert animals rely on triglycerides for metabolic water?

Triglycerides have ~2× more hydrogen than carbohydrates, generating more water upon oxidation

Which laboratory test is used to detect lipids in biological samples?

Ethanol emulsion test

Explain the function of triglycerides (use structure and properties)

Triglycerides are a long term energy storage in cells.

Their large non-powers hydrocarbon chains do not form hydrogen bonds in water, making them insoluble insoluble in water. Hence, they don’t affect water potential of storage cells.

There are 3 hydrocarbon chains per triglyceride, each with hydrocarbon chains made up of many C-H bonds. Upon oxidation, they produce twice as much ATP as that of the same mass of carbohydrates, making time a more compact energy store.

the ester bind between each hydrocarbon chain and glycerol backbone make it easily hydrolysed by lipases to produce ATP molecules upon the oxidation of fatty acids.