Lipids

Question 1

State the elements present in lipids (and the additional element needed to make phospholipids)

Answer 1

Carbon, Hydrogen, Oxygen + Phosphor

Question 2

Define the term “macromolecule”.

Answer 2

Complex molecules that have a relatively large molecular mass.

Question 3

State the 3 categories of lipids (or lipid derived molecules).

Answer 3

• Triglycerides
• Phospholipids
• Sterols

Question 4

Draw a labelled diagram showing the basic structure of a triglyceride. (Draw it on a piece of paper and check)

Answer 4

• Three fatty acid tails attached to one glycerol molecule

- They are synthesised by the formation of an ester bond.

Question 5

State the components of a triglyceride.

Answer 5

Three fatty acid tails and a glycerol head.

Question 6

State the difference between saturated, monounsaturated and polyunsaturated and how being one the other can change their properties.

Answer 6

saturated: no carbon-carbon double bonds between carbon atoms in their hydrocarbon tails. This means they can pack together as they are straight and are solid at RT.
monounsaturated/ Polyunsaturated: have at least one carbon double bond between carbon atoms. This causes them to bend or kink, meaning that cannot pack close together. This makes them liquid at RT. Monousaturated fatty acids have only one double bond.
Polyunsaturated fatty acids are the healthiest because they cannot be stored as solid fat, due to them being so bendy.

Question 7

Explain why saturated triglycerides tend to be solid (fats) at room temperature whereas unsaturated triglycerides tend to be liquid (oils).

Answer 7

Saturated triglycerides don’t have kinks so they can pack together tightly, meaning that there are more intermolecular interaction between the fatty acid chains. Therefore, it takes more energy to separate them.
Unsaturated triglycerides do have kinks so they bend and cannot pack closely together. Fewer intermolecular interactions. Takes less energy.

Question 8

Describe and explain how the melting point of a triglyceride would correlate with the length of the fatty acids it contained.

Answer 8

The longer the fatty acid chain the higher the melting point of the triglyceride. This is because longer fatty acids chain have a greater surface area for intermolecular interactions between them. This means that it takes more energy to break the chains apart, because there are a lot moreintermolecular interactions.
(Also, longer chain means more covalent bonds which are very hard to break).

Question 9

State the difference between the triglycerides found in non-fish animals and those in plants and fish.

Answer 9

Plants have unsaturated triglycerides and animals have saturated triglycerides.

Question 10

Draw a labelled diagram showing the basic structure of a phospholipid.

Answer 10

They have the same structure as a triglyceride expect on of their fatty acid tails is replaced by a phosphate group which is on the opposite side of the glycerol to the other two fatty acids. One of their fatty acids is saturated and the other is unsaturated.

Question 11

State the property that each end of the phospholipid has.

Answer 11

The phosphate group is hydrophilic - attracts and readily interacts with water molecules
Fatty acid tails are non-polar hydrophobic - they repel water and are insoluable in it.

Question 12

Draw a diagram to show how a triglyceride is formed and broken down.

Answer 12

Ester bonds are formed by a condensation reaction where a water molecule is released - esterification. The hydroxyl groups from the fatty acid tails and the glycerol interact to produce three water molecules and three ester bonds. Esterfication is another example of a condensation reaction.

When ester bonds are broken a hydrolysis reaction where a water molecule is used up the tricglyceride and the fatty acid tails break apart.

Question 13

Name the bond that holds the building blocks of a triglyceride together.

Answer 13

Ester bond

Question 14

State the number of water molecules produced in the production of one triglyceride.

Answer 14

Three water molecules

Question 15

State the products of digestion of a triglyceride (include partial digestion) and state what would happen to the pH of the solution (and why).

Answer 15

Products of digestion: free fatty acids and monoglycerides.

The PH of the solution would go down (more acidic) because you have free fatty acids (which are acids).

Question 16

Describe the structure of sterols/cholesterol.

Answer 16

They are complex alcohol molecules based on a four carbon ring structure with a hydroxyl group (OH) at one end. They have dual hydrophobic/ hydrophilic characteristics. The hydroxyl group is polar and so hydrophilic and the rest of the molecule is hydrophobic.

Question 17

List the functions of Triglycerides. (5)

Answer 17

• Insulation (slow conductors of heat so stored beneath skin of endotherm to maintain constant body temp)
• Store of energy (V. dense energy source, have x2 as much energy as carbs)
• Protection (fats stored around delicate organs)
• Buoyancy (less dense than water so insulated aquatic animals can float, this also aids breathing)
• Water source (hydrolysis of triglycerides can provide metabolic water)

Question 18

List the functions of Phospholipids (2)

Answer 18

• Cell Membrane - phospholipid bilayer with hymakes up part of the cell membrane and adds flexibility and acts as a barrier in the cell. The phospholipid bilayer has hydrophilic heads pointing out and a hydrophobic centre so water soluable substances can’t pass through easily.

Question 19

List the functions of Cholesterol (2)

Answer 19

• Plays a part in producing hormomes for cell communications. All the things that give us secondary sexual characteristics (i.e. sex hormones) are based in lipids.
• Cholesterol produces vitamins like vitamin D (fat soluable), steroid hormones and bile

Question 20

Describe how the presence of cholesterol affects the properties of cell membranes.

Answer 20

If a cell gets hot the phospholipids fall apart, if it’s cold they will clamp together. Cholesterol grabs on to the fatty acid tails and holds them together when it is too hot and keeps them apart when too cold.

Question 21

How to test for the presence of lipids?

Answer 21

1) Mix food sample with a small amount of ethanol
2) Move ethanol solution into a second test tube
3) Add distilled water
4) If cloudy emulsion appears, lipids are present

Question 22

How is the energy from lipids released?

Answer 22

When an enzyme called lipase breaks down lipids.

Question 23

Why do lipids contain so much energy?

Answer 23

The fatty acid chains of the triglycerides are hydro-carbons. The hydrogen and carbon bonds in these hydrocarbons contain a lot of energy, and this is released when the triglyceride is broken down.

Question 24

How can unsaturated fats be turned into saturated fats? (Give an example of this happening)

Answer 24

Unsaturated fats are made into saturated fats by bubbling it through hydrogen. This is called hydrogenation.
Vegetable oil —-> Margarine
(unsaturated) (saturated)
*Remember a side product of hydrogenation is transfats but these are always unsaturated.

Question 25

Give an example of a sterol

Answer 25

Cholesterol

Question 26

Why are transfats bad for you?

Answer 26

They are unsaturated fats but they do not have a kinked or bent chain so they still pack together as solid fats.
They do not have a bent chain because they hydrogen atoms on either side of the carbon-carbon double bond are on opposite side of the chain.

Question 27

Why is cholesterol carried as lipoprotein?

Answer 27

Cholesterol is a lipid so it is hydrophobic, but it still needs to be transported to cells in the blood stream. A lipoprotein is a soluable protein that cholesterol attaches to. Lipoproteins allow cholesterol to dissolve into the blood so that it can be tranported to cells.

Question 28

Where is cholesterol manufactured in the body?

Answer 28

The liver and intestines