Lipids

Question 1

Describe lipids

Answer 1

A diverse group of compounds which all contain carbon, hydrogen and oxygen

Question 2

Characteristics of lipids

Answer 2

• insoluble in water

* soluble in other lipids and organic solvent (e.g. ethanol, chloromethane, diethyl ether)

Question 3

Describe the composition of lipids

Answer 3

Larger number of carbon and hydrogen atoms than oxygen atoms

Significance??

Question 4

Describe triglycerides

Answer 4

• lipids made from one molecule of glycerol and 3 fatty acid molecules
• these molecules are not identical and are therefore not monomers; lipids are not polymers
• AKA: triacylglycerols, true fats, neutral fats

Question 5

Describe glycerol

Answer 5

An alcohol containing 3 carbon atoms each linked to a hydroxyl group

Question 6

Describe a fatty acid

Answer 6

• long chain of carbon and hydrogen atoms (a hydrocarbon chain) ending in an acidic carboxyl (-COOH) group
• (-COOH) ionises in water to release a hydrogen ion (proton), which gives fatty acids their acidic properties
• -COOH -COO- + H+

Question 7

Describe the formation of triglycerides

Answer 7

• each hydroxyl group on the glycerol molecule combines with a carboxyl group on a fatty acid molecule
• condensation reaction (water is released)
• an ester bond is formed

Question 8

Describe fats

Answer 8

• solid at RT (20°C)
• found in animals
• saturated fats

Question 9

Describe oils

Answer 9

• liquid at RT
• found in plants
• unsaturated fats

Question 10

Describe saturated fatty acids

Answer 10

• each carbon atom in the hydrogen carbon is linked to a carbon atom on each side and 2 hydrogen atoms
• the carbons are bonded to the maximum number of other atoms
• only contain single bonds in the hydrocarbon chain; the chain is relatively straight; triglycerides can pack closely together; solid at RT

Question 11

Describe unsaturated fatty acids

Answer 11

• the carbon atoms in the hydrocarbon chain are not bonded to the maximum number of other atoms
• two or more carbon atoms have a double bond between them

Question 12

Define monounsaturated fatty acids

Answer 12

Fatty acids with one double bond

Question 13

Define polyunsaturated fatty acids

Answer 13

Fatty acids with two or more double bonds

Question 14

Describe cis double bonds

Answer 14

• both CH2 groups are on top; causes a kink in the hydrocarbon chain
• prevents molecules from packing closely
• triglycerides with a high proportion are oils because attraction between molecules is weak

Question 15

Describe trans double bonds

Answer 15

• similar properties to saturated fatty acids; solid (straighter chain)
• vv unhealthy

Question 16

What is adipose tissue

Answer 16

Excess fat in mammals, laid down for storage in special connective tissue

Question 17

How do lipids compare to carbs and proteins?

Answer 17

• triglycerides have a higher proportion of hydrogen compared to carbohydrates or proteins
• they are a more concentrated source of energy
• each gram yield about 38kJ (more than double that of a gram of carbohydrate)

Question 18

How are lipids adapted for heat insulation?

Answer 18

• fat is a bad conductor of heat

* mammals increase adipose tissue in winter to reduce heat loss

Question 19

How are lipids adapted for shock absorption

Answer 19

• thick layers of adipose tissues are formed around delicate mammalian organs (e.g. kidneys) to stop them from being vulnerable to knocks and bumps

Question 20

How are lipids adapted for buoyancy

Answer 20

Many single-celled aquatic organisms produce an oil droplet to aid buoyancy

Question 21

Describe the composition of a phospholipid

Answer 21

• a molecule of glycerol attached to 2 fatty acid chains
• the third hydroxyl group of glycerol combines with phosphoric acid to form a polar phosphate group
• amphipathic -> one end of the molecule is hydrophilic (the head), and the other is hydrophobic (the tail)

Question 22

Why is the tail of a phospholipid hydrophobic

Answer 22

• the tail is the fatty acid chains

* these are oily

Question 23

Describe the phospholipid bilayer

Answer 23

• in water, phospholipid molecules collect together into a single (monomolecular) layer
• the hydrophilic heads poke into the water
• hydrophobic rails point inwards, away from watery environment
• gives cell membranes their fluid properties; allows lipid-soluble substances to pass easily though them

Question 24

Why does the phospholipid bilayer form

Answer 24

because, in cells, both the intracellular and immediate external environment are watery

Question 25

Describe waxes

Answer 25

• similar to triglycerides
• contain fatty acids joined to long-chain alcohols rather than glycerol
• usually relatively hard solids at room temperature
• provide protection and waterproofing on TBR surfaces of insects and leaves

Question 26

Describe steroids

Answer 26

• contain four rings of carbon and hydrogen atoms with various side chains
• many animal hormones are steroids (e.g. oestrogen, testosterone) -> made from cholesterol

Question 27

Describe cholesterol

Answer 27

• Raw material for the manufacture of vitamin D

* viral component in mammalian cell membranes; strengthens them at high temperatures