Lipids

Question 1

What are triglycerides and phospholipids?

Answer 1

Two groups of lipid

Question 2

How are triglycerides formed?

Answer 2

By the condensation of one molecule of glycerol and three molecules of fatty acid.

Question 3

How is an ester bond formed?

Answer 3

A condensation reaction between glycerol and a fatty acid (RCOOH)

Question 4

What are Lipids?

Answer 4

Biological molecules made of carbon, hydrogen and oxygen which are only soluble in organic solvents such as alcohols

Question 5

What are Triglycerides?

Answer 5

Lipids made of one molecule of glycerol and three fatty acids joined by ester bonds formed in the condensation reactions.

Question 6

What are fatty acids and describe their appearance

Answer 6

There are many different types of fatty acids (over
70 different types) which vary in chain length, presence and a number of double bonds.

• The R-group of a fatty acid may be saturated or unsaturated.

Question 7

What is a Saturated Lipid?

Answer 7

Saturated lipids don’t contain any carbon-carbon double bonds - such as those found in animal fats

Question 8

What is an Unsaturated Lipid?

Answer 8

unsaturated lipids contain carbon-carbon double bonds. - which can be found in plants

Question 9

What does the presence of double bonds mean in the properties of a molecule?

Answer 9

The presence of a double bond means that the molecule is able to bend. As a result, unsaturated fats cannot pack together as tightly and are therefore liquid at room temperature.

Question 10

What is a phospholipid?

Answer 10

one of the fatty acids of a triglyceride is substituted by a phosphate-containing group.

Question 11

Describe the structure and components of a phospholipid

Answer 11

• Phosphate heads are hydrophilic (loves/attracts water) and the tails are hydrophobic (hates/resists water) and as a result phospholipids form micelles when they are in contact with water.

The molecule is therefore known as polar

Question 12

What test is used to test for the presence of lipids

Answer 12

Emulsion Test

Question 13

How do you carry out an Emulsion Test?

Answer 13

1. Take a completely grease-free test tube and add 2cm3 of the sample to be tested and 5cm3 of ethanol.
2. Shake the test tube thoroughly to dissolve all the lipid in the solution.
3. Add 5cm3 of water and shake gently.
4. A cloudy-white colour indicates the presence of lipid.
5. As a control repeat the experiment using water as the sample, the final solution should remain clear.

Question 14

How is the phospholipid structure related to its properties

Answer 14

• In an aqueous environment being polar means a bilayer can be formed.
• The hydrophilic heads of the phospholipids can be used to hold at the surface of the cell surface membrane.
• Their structure allows them to form glycolipids with carbohydrates which are important on the cell surface membrane for cell recognition.

Question 15

How is the Triglyceride structure related to its properties

Answer 15

• High ratio of energy-storing carbon-hydrogen bonds to carbon atoms and therefore they are an excellent energy store.
• A low mass to energy ratio meaning that they are a good storage molecule, with a lot of energy being stored in a small volume. This is beneficial for animals as it is less mass to move around.
• Being large and non-polar lipids are insoluble in water and therefore their storage does not affect the water potential of cells.
• A high ratio of hydrogen-oxygen atoms means that triglycerides release water when they are oxidised and therefore provide an important source of water for organisms to live in dry environments.

Question 16

What are micelles?

Answer 16

The products of lipase digestion remain in association with the bile salts to form structures. (Travel through the ileum)

Question 17

The word hydrolysis is defined as the lysis of water. How does this apply to polymers?

Answer 17

Polymers break by separating water into hydrogen and hydroxyl groups that are added to the monomers.

Question 18

What are three functions that lipids serve in plants and/or animals?

Answer 18

Lipids serve in the storage of energy, as a structural component of hormones, and as signalling molecules.

Question 19

How do phospholipids contribute to cell membrane structure?

Answer 19

Phospholipids orient their heads towards the polar molecules and tails in the interior of the membrane, thus forming a bilayer

Question 20

What type of compound functions in hormone production, contributes to membrane flexibility, and is the starting molecule for bile salts?

Answer 20

Cholesterol, which is a lipid and also steroid, functions here

Question 21

Cholesterol is a precursor to hormones, such as testosterone. Testosterone is a male sex hormone that has a key role in sperm production.

How is testosterone most likely to enter target cells?

Answer 21

Directly through the membrane

Question 22

Amphipathic molecules are both hydrophobic and hydrophilic. Which of the following molecules could be described as amphipathic?

Answer 22

Phospholipids

Question 23

Relate the structure of triglycerides to their functions.

Answer 23

• High energy: mass ration = high calorific value from oxidation (energy storage)
• Insoluble hydrocarbon chain - won’t affect ψ
  Used for waterproofing
• Slow conductor of heat = thermal insulation eg adipose tissue
• Less dense than water = buoyancy of aquatic animals

Question 24

Describe the structure and function of phospholipids.

Answer 24

Amiphiatic molecule:glycerol backbone attached to 2 hydrophobic fatty acid tails & 1 hydrophilic polar phosphate head

• Forms phospholipid bilateral in water = component of membranes
• Tails can splay outwards = waterproofing

Question 25

Compare phospholipids and triglycerides

Answer 25

• Both have glycerol backbone
• Both may be attached to a mixture of saturated, monounsaturated & polyunsaturated fatty acids.
• Both contain C,H,O
• Both formed by Condensation reactions.

Question 26

Contrast phospholipids and triglycerides

Answer 26

Phospholipids:

• 2 Fatty acids & 1 phosphate group attached
• Hydrophilic head & hydrophobic tail
• Used in primarily in membrane formation

Triglycerides
• 3 Fatty afire attached
• Entire molecule is hydrophobic
• Used primarily as storage molecule (oxidation releases energy)

Question 27

What is the most common number of carbon atoms found is fatty acids?

Answer 27

12-18 carbons

Question 28

emulsion

Answer 28

Small droplets of a substance are suspended in another solution

Question 29

when testing for a lipid how many minutes do you leave the test upright for

Answer 29

2-3 minutes