3.5 Lipids

Question 1

What elements do lipids contain?

Answer 1

Carbon, Hydrogen and Oxygen

Question 2

What are lipids commonly known as?

Answer 2

Fats and oils.

Question 3

Are lipids polar or non-polar?

Answer 3

Non-polar, the electrons in outer orbitals are evenly distributed

Question 4

What are lipids built from?

Answer 4

Repeating monomers

Question 5

Are lipids macro or micromolecules?

Answer 5

Macromolecules; they are large complex molecules

Question 6

What is the structure of a triglyceride?

Answer 6

One glycerol molecules combined with 3 fatty acids (fatty acids are either all identical or all different)

Question 7

What functional group do fatty acids belong to?

Answer 7

Carboxyl group (-COOH)

Question 8

Describe the structure of a fatty acid.

Answer 8

A hydrocarbon attached to the carboxyl functional group.

Question 9

Describe the general formula for a fatty acid.

Answer 9

RCOOH (Where R is the variable number of carbon and hydrogen atoms)

Question 10

What do both glycerol and fatty acids contain?

Answer 10

Hydroxyl groups (OH)

Question 11

How does a triglyceride form?

Answer 11

The hydroxyl groups of the fatty acids and the glycerol interact in a condensation reaction, formation 3 water molecules and an ester bond between the fatty acids and glycerol molecule.

Question 12

What is the formula for an ester bond?

Answer 12

RCOOR

Question 13

What kind of reaction is required to break down a triglyceride?

Answer 13

A hydrolysis reaction. The three water molecules produced in the condensation reaction need to be supplied back.

Question 14

What makes a fatty acid saturated, and why?

Answer 14

If they have no double bonds between the carbon atoms, because all teh carbon atoms have formed the maximum number of bonds with hydrogen atoms (they are saturated with hydrogen bonds)

Question 15

What is the name for if there is one double bond in a fatty acid?

Answer 15

Monounsaturated

Question 16

What is the name for if there are two or more double bonds in a fatty acid?

Answer 16

Polyunsaturated

Question 17

Why are saturated fatty acids liquids at room temperature?

Answer 17

Because the presence of double bonds causes the molecule to bend, so they cannot pack so closely together.

Question 18

What is the general formla for a saturated fatty acid?

Answer 18

CnH2n+1 COOH

Question 19

Why are lipids long-term energy stores?

Answer 19

Because when fats/oils are hydrolysed, a large amount of energy is released (because the bonds between carbon and hydrogen in the fatty aids contain large amounts of energy).

Question 20

Describe the structure of a phospholipid.

Answer 20

2 fatty acids are bonded to a glycerol molecule. This glycerol molecule is attached to a phosphate group

Question 21

What is a phosphate group?

Answer 21

The same as a phosphate ion. PO4 (3-)

Question 22

What are the two key sections of a phospholipid?

Answer 22

Hydrophobic tails (two fatty acids), hydrophilic head (the glycerol and phosphate group)

Question 23

Is phosphate polar or non-polar?

Answer 23

Polar (all ions are polar)

Question 24

Is the hydrophilic head of a phospholipid charged?

Answer 24

Yes, negatively charged

Question 25

Are the hydrophobic tails of a phospholipid charged?

Answer 25

No

Question 26

Describe what happens to a phospholipid when in water.

Answer 26

-The hydrophilic head will interact and dissolve in the water
-Hydrophobic fatty acid tails will stick out of the water
-Phospholipids form a monolayer on the surface of the layer
-Phospholipids are insoluble in water

Question 27

What is the name of the structure that phospholipids form when in an aqueous environment?

Answer 27

Two-layered sheet formation (bilayer)

Question 28

Describe the bilayer that phospholipids form when in an aqueous solution.

Answer 28

Hydrophobic tails point towards the centre of the sheet, protected from the water by hydrophilic heads

Question 29

Why do phospholipids play a key role in forming cell membranes?

Answer 29

Because of the bilayer arrangement that they form, and because they can therefore separate an aqueous environment from the aqueous cytosol within cells.

Question 30

What chemical do you use to test for lipids?

Answer 30

Ethanol

Question 31

Describe the method for testing for lipids.

Answer 31

1) If testing solid food, grind up the food using a pestle or mortar
2) Add a solvent, like ethanol, to the food sample
3) Place a bung in the test tube and shake thoroughly so that any lipid will dissolve in the solvent
4) Decant the lipid/solvent mixture into a test tube of distilled water
5) The presence of a white emulsion (cloudy) indicates the presence of a starch
6) The degree of cloudiness indicates the amount of lipid present

Question 32

What is a sterol?

Answer 32

A type of alcohol

Question 33

Describe the two ends on a sterol.

Answer 33

One hydroxyl, polar, hydrophilic end and one non-polar, hydrophobic end

Question 34

What is an important use of cholesterol?

Answer 34

Used in the structure of cell membranes, to add stability and regulate their fluidity, by keeping the membrane fluid at a low temperature.

Question 35

Describe the relationship between cholesterol and phospholipids in the cell membrane

Answer 35

The hydrophilic ened of the cholesterol molecule is attracted to the hydrophilic heads of the phospholipid.

Question 36

Where does the body manufacture cholesterol?

Answer 36

In the liver and intestines

Question 37

What are the biological roles of lipids that they have due to their non-polar nature?

Answer 37

-Membrane formation (formation of hydrophobic barriers)
-Hormone production
-Electrical insulation necessary for impulse transmission
-Waterproofing (eg in bird’s feathers)
-Buoyancy for aquatic animals
-Cushioning to protect vital organs
-Thermal insulation to reduce heat loss.