Lipids

Question 1

What is a triglyceride?

Answer 1

A fat made up of ONE glycerol molecule and THREE fatty acids.

Question 2

What is glycerol?

Answer 2

Glycerol is a simple polyol compound (member of the alcohol family)

Question 3

What are fatty acids?

Answer 3

A carboxylic acid with a long aliphatic chain , either saturated or unsaturated.

Question 4

(typical) Difference between fats and oils.

Answer 4

Fats are SATURATED lipids that are SOLID at RTP.

Oils are UNSATURATED lipids that are LIQUID at RTP.

Question 5

Why are lipids not soluble in water?

Answer 5

Lipids are non polar - the electrons are distributed evenly in the outer orbital - and so there are no positive or negative areas around the molecule.

Question 6

What type of molecule are lipids?

Answer 6

Lipids are large complex molecules known as MACROMOLECULES.

Question 7

What are the bonds between glycerol and fatty acids called?

Answer 7

Ester bond

Question 8

How does the bond between glycerol and fatty acids arise?

Answer 8

Both types of molecules contain hydroxyl groups and these interact to produce three water molecules and three ester bonds.

HYDROGEN from GLYCEROL
HYDROXIDE from FATTY ACIDS

Question 9

What is esterification an example of?

Answer 9

Condensation reaction

Question 10

Formula for fatty acids (extra) ?

Answer 10

C=O(CH2)nCOOH

Question 11

Formula for Glycerol?

Answer 11

C3H8O3

Question 12

Why are oils liquid at room temp?

Answer 12

They are unsaturated compounds, and the double carbon=carbon bond causes the chain to bend, so they cannot be packed as close together.

Question 13

What is a phospholipid?

Answer 13

A modified triglyceride, containing ONE glycerol molecule, TWO fatty acids, and ONE phosphorous atom

Question 14

_________ phosphate ions are found in the cytoplasm.

What is the formula for this ion?

Answer 14

Inorganic, PO4,3-

Question 15

Why are phosphate ions soluble in water?

Answer 15

Contain 3 extra electrons, so are charged.

Question 16

What does hydrophobic mean?

Answer 16

Repels water

Question 17

What does hydrophilic mean?

Answer 17

Attracts water

Question 18

How would you identify whether a molecule is hydrophobic or hydrophilic?

Answer 18

Hydrophilic— polar/charged

Hydrophobic— non polar/not charged

Question 19

Describe the structure of phospholipids according to ‘heads’ and ‘tails’

Answer 19

Phospholipids have hydrophilic heads- the phosphate atom- and hydrophilic tails- the fatty acids.

Question 20

How area phospholipids arranged in the bilayer? Why is this useful?

Answer 20

They are arranged with the hydrophilic heads facing out of the membrane and the hydrophobic tails pointing towards the cytoplasm. Like this, the cell’s aqueous cytosol is kept separate from the aqueous environment outside.

Question 21

What are sterols?

Answer 21

Steroid alcohols, a type of lipid found in cells.

Question 22

What is the structure of sterols?

Answer 22

4 carbon ring ring structure and a hydroxyl group which is polar and so is hydrophilic, the rest of the molecule is hydrophobic.

Question 23

What is cholesterol?

Answer 23

Cholesterol is a sterol. The body mainly produces cholesterol in the liver and intestines.

Question 24

Structure of cholesterol?

Answer 24

Hydrophilic hydroxyl group

Hydrophobic rest of molecule

Question 25

How is cholesterol involved in the cell membrane?

Answer 25

It is positioned between the phospholipids, as the hydrophilic tail (hydroxyl group) of cholesterol is attracted to the hydrophilic head of the phospholipids, and vice versa. The hydroxyl group is at the PERIPHERY of the membrane.

Question 26

Why is the positioning of cholesterol in the bilayer useful?

Answer 26

It adds stability to cell membranes as it regulates their fluidity, making sure it’s fluid at low temps and not too fluid at high temps.

Question 27

What are manufactured from cholesterol in the body?

Answer 27

Vitamin D, steroid hormones and bile.

Question 28

What roles do lipids play due to their non polar nature? (4)

Answer 28

- membrane formation and the creation of hydrophobic barriers - hormone production - waterproofing e.g. in birds feathers - electrical insulation necessary for impulse transmission

Question 29

Lipids (triglycerides) play an important role in long-term energy storage. Where are they stored and why?

Answer 29

Under the skin and around vital organs —thermal insulation —cushioning to protect vital organs —buoyancy for aquatic organisms

Question 30

What is the test to identify lipids?

Answer 30

Emulsion test

Question 31

Outline the steps in the emulsion test for lipids

Answer 31

1. Sample mixed with ethanol 2. Solution mixed with water and shaken 3. White layer forms, lipid is present.

Question 32

Why is ethanol added to lipids (during the emulsion test) ? Explain why this happens.

Answer 32

To dissolve the lipids in the ethanol. Because lipids are insoluble in water, as they are non polar organic compounds, so will be soluble in organic solvents

Question 33

Why is water added in the emulsion test?

Answer 33

Ethanol (previously added) is soluble in water, while lipids are not, so they fall out and form a cloudy white, insoluble layer

Question 34

What lipids are in plants?

Answer 34

UNSATURATED triglycerides, occur mainly as oils

Question 35

What lipids are in our diet?

Answer 35

Animals (that we eat)(but generally not fish) contain saturated triglycerides.

Question 36

What are better, unsaturated or saturated triglycerides for our diets?

Answer 36

Unsaturated. | Saturated fats were thought to cause coronary heart disease, it recent evidence contradicted this.

Question 37

What are cis fats?

Answer 37

Where the hydrogens are on the same side as the double bond. H H | | C=C

Question 38

What are trans fats?

Answer 38

``` When the hydrogens are on opposite sides of the double bond. H | C=C | H ```

Question 39

Why is it good to have a low overall saturated fat intake?

Answer 39

Saturated fats are more closely packed together and so have a higher energy intake but this can lead to obesity

Question 40

What is the problem with trans fats?

Answer 40

Add

Question 41

Why are phospholipids known as surfactants?

Answer 41

They arrange themselves in a way that the hydrophilic heads face the water and the hydrophobic tails against.

Question 42

where are lipids to provide electrical insulation?

Answer 42

in nerve cells

Question 43

where are lipids to provide thermal insulation?

Answer 43

blubber, adipose tissue

Question 44

phospholipids are amphipathic, what does this mean?

Answer 44

have both hydrophobic and hydrophilic properties