section 2: biological molecules - topic 4: lipids

Question 1

what are lipids?

Answer 1

macromolecules.

Question 2

what do all lipids contain?

Answer 2

carbon.
hydrogen.
oxygen.

Question 3

what are the 3 types of lipids?

Answer 3

triglycerides.
phospholipids.
cholesterol.

Question 4

what is the structure of a triglyceride?

Answer 4

they have 1 molecule of glycerol with 3 fatty acids attached to it.

Question 5

how are triglycerides formed?

Answer 5

they’re synthesised by the formation of an ester bond between each fatty acid and the glycerol molecule.

Question 6

how many ester bonds does 1 triglyceride molecule have?

Answer 6

3.

Question 7

how is each ester bond formed?

Answer 7

by a condensation reaction.

Question 8

what is the process called in which triglycerides are synthesised?

Answer 8

esterification.

Question 9

how is an ester bond broken?

Answer 9

in a hydrolysis reaction.

Question 10

what is the structure of fatty acids?

Answer 10

they have long ‘tails’ made of hydrocarbons.
the ‘tails’ are hydrophobic.
the tails make lipids insoluble in water.

all fatty acids have the same basic structure, but the hydrocarbon tail varies.

Question 11

what are the 2 kinds of fatty acids?

Answer 11

saturated.
unsaturated.

the difference is in their hydrocarbon tails.

Question 12

what is the stricture of saturated fatty acids?

Answer 12

they don’t have any double bonds between their carbon atoms in their hydrocarbon tails.

Question 13

what is the structure of unsaturated fatty acids?

Answer 13

they have at least 1 double bond between carbon atoms - causes the chain to kink.

Question 14

what is the difference between phospholipids and triglycerides?

Answer 14

they are pretty similar, except the 1 of the fatty acid molecules is replaced by a phosphate group.

phosphate group = hydrophilic.
fatty acid tails = hydrophobic.

Question 15

what is the structure of cholesterol?

Answer 15

has a hydrocarbon ring structure attached to a hydrocarbon tail.

the ring structure has a poly hydroxyl (OH) group attached to it.

Question 16

what do animals and plants use triglycerides for?

Answer 16

mainly used as energy storage molecules.

Question 17

what do some bacteria use triglycerides for?

Answer 17

to store both energy and carbon.

Question 18

why are triglycerides good for storage?

Answer 18

because the long hydrocarbon tails of the fatty acids contain lots of chemical energy.
^ a load of energy is released when they’re broken down.

Question 19

how are triglycerides insoluble?

Answer 19

they bundle together as insoluble droplets in cells because the fatty acid tails are hydrophobic.
^ the tails face inwards - shielding themselves from water with their glycerol heads.

Question 20

why is triglycerides being insoluble useful?

Answer 20

because they don’t cause water to enter the cells by osmosis - which would make them swell.

Question 21

where are phospholipids found?

Answer 21

in the cell membranes of all eukaryotes and prokaryotes.

they make up the phospholipid bilayer.

Question 22

describe the phospholipid heads & tails.

Answer 22

heads = hydrophilic.
tails = hydrophobic.

Question 23

what is the function of cholesterol in eukaryotes?

Answer 23

help strengthen the cell membrane by interacting with the phospholipid bilayer.

Question 24

what is the structure of cholesterol?

Answer 24

has a small size and flattened shape.
^ allows cholesterol to fit in-between the phospholipid molecules in the membrane.

Question 25

how does cholesterol act upon the membrane?

Answer 25

bind to the hydrophobic tails of the phospholipids, causing them to pack more closely together.
^ this helps to make the membrane less fluid and more rigid.