3.5 - Lipids

Question 1

What are the characteristics of lipids?

Answer 1

Non-polar

Macromolecules (not polymers)

Made of CHO

Question 2

What are the components of triglycerides?

Answer 2

1 glycerol molecule + 3 fatty acids

Question 3

Describe the formation of triglycerides.

Answer 3

Glycerol (C3H8O3) hydrogen atoms and the hydroxyl groups on the end of the fatty acids are eliminated to form 3 water molecules and a triglyceride.

The bond formed in place of the eliminated water, is an ester bond through esterification.

Question 4

What is esterification?

Answer 4

Formation of an ester bond ( 0-C=0 )

Formed when a carboxylic acid reacts with an alcohol.

Question 5

What is a saturated fatty acid?

Answer 5

Fatty acid chains with no double bonds

Examples: solid fats in animals

Question 6

What is an unsaturated fatty acid, and what are the types?

Answer 6

Fatty acid chains with double bonds, provides a kink in the chain

Examples: Liquid fats (oils) from plants

MONOUNSATURATED - C=C double bond

POLYUNSATURATED - 2 or more C=C double bonds

Question 7

What is the effect of a C=C double bond in a fatty acid?

Answer 7

The kink in the chain means they cannot pack as tightly together, leaving UNSATURATED fatty acids liquid at RT.

SATURATED fatty acids are solid at RT as they can pack tightly together,

Question 8

What are the biological roles of lipids?

Answer 8

• Membrane formation
• Hydrophobic barriers
• Hormone production
• Electrical insulation for impulse transmission
• Waterproofing e.g. plant leaves

Question 9

What are the roles of lipids (triglycerides specifically) regarding long term energy storage?

Answer 9

• Thermal insulation, reduces heat loss
• Cushioning - protects vital organs (e.g. heart and kidney)
• Buoyancy for aquatic animals (e.g. whales)

Question 10

Describe the test for identification of lipids.

Answer 10

EMULSION TEST

1) Mix sample with ethanol
2) Add water and shake
3) For lipid positive result, white emulsion later forms on top

If -ve, clear solution forms.

Question 11

What is a phospholipid?

Answer 11

Modified triglyceride with the element phosphorus, alongside CHO.

Inorganic PO4(3-), phosphate ions are in each cell’s cytoplasm. (They are -vely charged).

Question 12

What is the structure of a phospholipid?

Answer 12

One fatty acid of the triglyceride is replaced with a phosphate group head which is HYDROPHYLIC (water loving due to it being charged and the water polar)

• Non-polar tail (fatty acid chains), they are repelled by water. HYDROPHOBIC
• Mix with fats

Question 13

How do phospholipids interact with water?

Answer 13

They form a layer in water due to the hydrophilic heads being attracted to the water.
- The hydrophobic tails stick out of the water. as they are repelled.

Question 14

What is a surfactant?

Answer 14

Surface active agent
Something which lowers the surface tension of a liquid
(phospholipids are surfactants)

Question 15

What roles do phospholipids play in cell membranes?

Answer 15

They are key in cell surface (plasma membranes)

• They form a bilayer with they hydrophilic tails pointing inwards.
• They separate the aqueous cytosol from the aqueous external environment of the cell.

Question 16

What is a sterol?

Answer 16

STEROID ALCOHOL

• Type of liquid in cells
• Complex alcohol molecule with a 4 carbon ring structure and a hydroxyl group at the end.
• Have dual hydrophobic (whole molecule bar the hydroxyl) and hydrophilic (hydroxyl group due to its polarity) capabilities

Question 17

Where is cholesterol manufactured?

Answer 17

Manufactured in the liver and intestines. It is a sterol

Question 18

What are the roles of cholesterol?

Answer 18

Positioned between phospholipids with its hydroxyl group at the periphery of the plasma membrane.

• gives membrane stability
• Regulates fluidity keeping membrane fluids at low temperature, stopping them becoming too fluid at high temps.