lipids

Question 1

What is a triglyceride and how do they form

Answer 1

Lipid molecule consisting in 1 glycerol and 3 fatty acids. They are non polar and hydrophobic
condensation reaction between 1 molecule of glycerol and 3 fatty acids which form ester bonds
They have 3 ester bonds

Question 2

contrast saturated and unsaturated fatty acids

Answer 2

saturated
- contain only single bonds
- straight chain molecules have many contact points
higher melting point = solid at room temperature
found in animal fats
unsaturated
- contain C=C double bonds
- kinked molecules have fewer contact points
lower melting point = liquid at room temperature
- found in plant oils

Question 3

What are the function of lipids

Answer 3

Energy source for respiration
thermal insulation
Electrical insulation
Protection
Membrane structure
Steroid hormones

Question 4

are phospholipids and triglycerides polymers

Answer 4

no they are not repeating units they are macromolecules

Question 5

describe the structure and function of cholesterol

Answer 5

steroid structure of 4 hydrocarbon rings
hydrocarbon tail on one side, hydroxyl group (-OH) on the other side
adds stability to cell surface phospholipid bilayer by connecting molecules
at low temps cholesterol increases membrane fludiity to stop the membrane solidifying - packs less closely togather

structure
what does it do to the phospoholipid bilayer

Question 6

type of bond formed when fatty acids bond with glycerol

Answer 6

ester bond

Question 7

phospholipid is therefore made up of what two parts

Answer 7

1. hydrophilic ‘head’ which interacts with water but no fat
2. hydrophobic ‘tail’ which orients itself away from water but mixes readily with fat

Question 8

describe how triglycerides may differ from each other

Answer 8

the glycerol molecule in all fatty acids is the same
the difference in fats and oils comes from variation in the fatty acid - saturated or unsaturated

Question 9

contrast the difference from phospholipids and triglycerides

Answer 9

triglycerides have 3 fatty acids and 3 ester bonds whereas phospholipids have 2 fatty acids and 2 ester bond

Question 10

Define lipid

Answer 10

A group of substances that are soluble in alcohol rather than water due to fewer -OH groups
They include phospholipids, glycolipids, and cholesterol

Question 11

Are lipids soluble in water + why

Answer 11

They are insoluble in water
They are not polar molecules

Question 12

Structure of glycerol

Answer 12

Three carbon backbone with an alcohol -OH attached to each carbon

Question 13

Structure of fatty acids

Answer 13

They have a carboxylic acid group -COOH and a variable ‘R’ group

Question 14

How do lipids act as an energy source

Answer 14

Can be broken down in respiration to generate energy and release ATP by hydrolysing the ester bonds and the glycerol and fatty acids until completely broken down into carbon dioxide and water
Insoluble in water so can be stored in cells without affecting the water potential - no osmotic effect

Question 15

How do lipids act as an thermal insulation

Answer 15

adipose tissue is a storage location for lipids in mammals acting as a heat insulator.

Question 16

how does lipids act as an electrical insluation

Answer 16

nerve fibres are suurounded by a fatty mylein sheath

Question 17

how do lipids act as a steriod hormones

Answer 17

steriod hormones are all made from the lipid cholesterol

Question 18

how do lipids help with buoyancy

Answer 18

because fat is less dense than water - used by aquatic animals to help them float

Question 19

how do lipids help with protection

Answer 19

human have a fat around delicate organs such as the kidneys to act as a shock absorber. the peptidoglycan cell wall of some bacteria is covered in a lipid rich outer coat

Question 20

What is the structure of a phospholipid

Answer 20

Glycerol
2 fatty acids
A phosphate group

Question 21

what sort of reaction forms a phosopholipid

Answer 21

condensation

Question 22

what type of bond is there between a phosophate group and a glycerol in a phosopholipid

Answer 22

Ester bond

Question 23

how do phosopholipids interact with water molecules

Answer 23

Hydrophilic head and a hydrophobic tail

Question 24

What type of molecule is a phospholipid

Answer 24

Amphipathic

Question 25

what is the usage of lipid normally means its amphipathic

Answer 25

Membrane lipids

Question 26

how do phosopholipids react when in contact with water

Answer 26

tails stick up with head forming layer of the surface or might form a micelle (ball with heads on the ouside and tails on the inside

Question 27

what structure do phosopholipids form when forming a membrane

Answer 27

A bilayer

Question 28

what gives a phosopholipid membrane bilayer its stability

Answer 28

individual phosopholipids are free to move around in their layer but will not move to any position that exposes the hydrophobic tails

Question 29

what allows the membrane to be selectively permeable

Answer 29

it is only possible for small, non-polar molecules to move through the bilayer

Question 30

Contrast cholesterol to phospholipids/triglycerides

Answer 30

Cholesterol is not made up of glycerol and fatty acids
phospholipids and triglycerides are made up of glycerol and fatty acids

Question 31

What is cholesterols role in the membrane

Answer 31

Regulates the fluidity of the membrane

Question 32

What is cholesterol made

Answer 32

In the liver of animals

Question 33

phospholipid molecules are similar to triglycerides but they also contain the element phosphorus as part of the phosphate group
explain how the structure of phospholipids allows them to form the bilayer of a plasma membrane
(3 marks )

Answer 33

hydrophilic head and hydrophobic tails (1)
hydrophobic part / tails, repelled, by water (1)
head / hydrophilic part, forms H bonds with water (1)
idea that medium outside / inside plasma membrane is aqueous (1)
idea that hydrophobic nature of tails results in their facing towards each other (10

Question 34

state two roles of cholesterol in living organisms

Answer 34

regulates fluidity of / stabilises phospholipid bilayer
converted to a steroid
making bile
making vitamin D

Question 35

phospholipid molecules also contain fatty acids
explain how the fatty acids in phospholipids allow the formation of membrane

Answer 35

fatty acids are hydrophobic so do not interact with water
form a phospholipid bilayer
hydrophobic nature causes the fatty acid tails to orientate towards the middle of the bilayer

Question 36

what do carbon-carbon double bonds do to the number of hydrogens

Answer 36

decreases the number of hydrogens