lipids

Question 1

what functional group do all fatty acids contain

Answer 1

carboxyl

Question 2

features of saturated fatty acids (4)

Answer 2

• contain a c-c single bond
• bonded to maximum number of hydrogen bonds
• made up of stearic (straight) chains
• high melting point, solid at room temperature

Question 3

why do saturated fatty acids have a high melting point

Answer 3

the triglyceride molecules are tightly packed with lots of contact

Question 4

features of unsaturated fatty acids (4)

Answer 4

• contain c=c double bond
• bonded to ‘less’ hydrogen
• made up of a bent chain
• lower melting point, liquid at room temperature

Question 5

why do unsaturated fatty acids have a lower melting point

Answer 5

molecules are less tightly packed

Question 6

describe the formation of a triglyceride molecule

Answer 6

• one glycerol bonds with 3 fatty acids
• condensation reaction releasing three water molecules
• ester bonds form
• between hydroxyl groups on glycerol and carboxylic groups on fatty acids

Question 7

describe the formation of a phospholipid bilayer

Answer 7

• hydrophobic phosphate heads face outwards attracted to water
• found both inside and outside the cell
• hydrophobic fatty acid tails turn inwards repelled by water

Question 8

describe the structure of a phospholipid

Answer 8

contains a charged hydrophilic phosphate ‘head’, a glycerol molecule and hydrophobic fatty acid tails (two fatty acids)

Question 9

What are the roles of lipids (5)

Answer 9

• store of energy (to produce ATP through respiration)
• insulation
• protection
• waterproofing (e.g waxy cuticle on leaves)
• production of phospholipids for formation of cell surface/organelle membranes

Question 10

similarities of triglycerides and phospholipids

Answer 10

• both insoluble
• both have ester bonds

Question 11

describe the test for lipids

Answer 11

if the sample is solid, grind it. mix this sample with 2cm^3 of ethanol and 2cm^3 of water. shake. if positive, solution will go from colourless to a white/milky emulsion

Question 12

describe a triglyceride molecule

Answer 12

-1 glycerol bonded to three fatty acids
- hydrophobic (non-polar) molecule

Question 13

describe a phospholipid

Answer 13

• 1 glycerol bonded to two fatty acids, third replaced by a phosphate group
• hydrophilic head, hydrophobic tail
• unlike triglycerides it forms micelles in water

Question 14

describe the roles of phospholipid bilayers in the cell surface membrane

Answer 14

partially controls substances in and out of the cell

Question 15

what molecules can diffuse directly through the bilayer in a cell surface membrane

Answer 15

non-polar or lipid soluble molecules

Question 16

what molecules can’t diffuse directly through the bilayer in a cell surface membrane and how do they pass through

Answer 16

hydrophilic, polar, charged molecules. require protein transport channels

Question 17

describe the role of the phospholipid bilayer in the organelle membrane

Answer 17

• control entry/exit of substances
• isolates enzymes
• separates organelle contents from cytoplasm to allow specific metabolic reactions
• provides a surface for biochemistry