L3 - Lipids

Question 1

What are the 2 groups of lipids?

Answer 1

Triglycerides and phospholipids

Question 2

How are triglycerides formed?

Answer 2

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

Question 3

What forms an ester bond?

Answer 3

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

One water molecules is released per ester bond

Question 4

What 2 forms can the R-group of a fatty acid be?

Answer 4

saturated or unsaturated

Question 5

What happens in phospholipids?

Answer 5

In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group

Question 6

What are triglycerides mainly used as?

Answer 6

As energy store molecules

Question 7

What type of bond forms beteren glycerol and the fatty acid chains?

Answer 7

Ester bonds

Question 8

How many molecules of water are released per 1 triglyceride bond?

Answer 8

3 molecules of water

Question 9

What is the structure of fatty acids?

Answer 9

Long ‘tails’ made of a chain of hydrocarbon with 4-36 carbon atoms
(Most have 12-18)

Glycerol links to the central carbon atom on fatty acids

Question 10

What are triglycerides function in energy release?

Answer 10

Chemical energy is stored in the fatty acid hydrocarbon tails

So lots of energy is released when triglycerides are broken down

Question 11

How does the amount of energy contained in lipids compare to carbs?

Answer 11

Carbs contain half the amount of energy per gram lipids do

Question 12

Why do triglycerides repel water?

Answer 12

They are insoluble in water because the fatty acid tails are hydrophobic

Meaning the cell’s water potential isn’t affected by triglycerides

If they didn’t repel water, water would enter the cell through osmosis causing the cell to swell up

Question 13

Why do the insoluble triglycerides crowd together at droplets in cells?

Answer 13

Because the hydrophobic fatty acid tails face inwards

Question 14

What do phospholipids do?

Answer 14

Form a bilayer which controls what comes in and out of the cell

Question 15

What is the structure of phospholipids?

Answer 15

Composed of fatty acid chains attached to glycerol

Has 2 hydrophobic fatty acid tails and 1 hydrophilic phosphate group
Making it an amphipathic molecule

Question 16

What do the hydrophobic tails of phospholipids do?

Answer 16

They can’t interact with water

In membranes, they face inwards in the bilayer

This means water-soluble substances can’t easily pass through the membrane

Question 17

What does the hydrophilic head of phospholipids do?

Answer 17

It can interact with water

In membranes, it faces outwards

Question 18

What is the structure of saturated fatty acids?

Answer 18

Carbon atoms have single bonds in between them in the hydrocarbon chain

The number of hydrogen atoms attached to the carbon skeleton is maximised

Question 19

What are saturated fatty acids like at room temperature?

What are they also linked to?

Answer 19

Solid at room temp and usually of animal origin

Linked to increased risk of cardiovascular disease in humans

Question 20

What foods contain a high proportion of saturated fat?

5

Answer 20

Cream
Cheese
Butter
Other whole dairy products
Fatty meats

Question 21

What is the structure of unsaturated fatty acids?

Answer 21

Have one or more double bonds between carbon atoms in the hydrocarbon chain

Question 22

What is an example of an unsaturated fat?

Answer 22

Cooking oils

Question 23

What are unsaturated fats like at room temperature?

Answer 23

Double bonds ‘kink’ the carbon chain so unsaturated fats can’t pack tightly together

Causing them to remain liquid at room temperature

Question 24

Is the phosphate head of phospholipids positively or negatively charged?

Answer 24

Negatively charged

Question 25

What are the 3 main functions that lipids serve in plants and/or animals?

Answer 25

Storage of energy

A structural component of hormones

As signalling molecules

Question 26

How do phospholipids contribute to cell membrane structure?

Answer 26

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