lipids Flashcards
what is the main characteristic of lipids?
insoluble in water but soluble in organic solvents
components of lipids? what is the general formula of lipids?
carbon, hydrogen, oxygen
unlike carbohydrates, there is no fixed structure
therefore, if the formula is not in the form of carbohydartes, its more likely a lipid
state the difference between oils and fats
fat: lipid at solid state at 20°C
oil: lipid at liquid state at 20°C
state the difference between simple and compound lipids
simple: made up of fatty acids with various alcohols
compound: has lipid and non-lipid components
give an example of a simple and compound lipid, including what they are composed of
simple: fats/triglyceride, esters of fatty acids with glycerol
compound: phospholipid, lipids made up of fatty acids + alcohol + phosphate
what are fats/triglyceride composed of?
glycerol + 3 molecules of fatty acids
describe and sketch the structure of glycerol
alcohol with three carbons, each bearing a hydroxyl group (-OH)
structure
describe fatty acids
- consists of hydrocarbon chain and carboxyl group (-COOH)
- may be saturated / unsaturated
describe the hydrocarbon chains in fatty acids
consists of chain of carbon atoms to which hydrogen atoms are attached.
they vary in length, but they are most commonly even numbered chains between 14 to 20 carbon
describe the structure of saturated fatty acids
- general formula: RCOOH, where R is a hydrocarbon chain made entirely of single C-H and C-C bonds
- hydrocarbon chain does not does not contain any carbon-carbon double bond and contains the maximum number of hydrogen atoms possible
describe the state of fats with high content of saturated fatty acids at room temperature, and state what living organisms always produces saturated fats
- solid at room temperature, higher melting point
- animals
describe the structure of unsaturated fatty acids
- contains carbon-carbon double bonds, which causes kink(s) in hydrocarbon chain
- if a fatty acid has more than one double bond, it is polyunsaturated
a) describe AND explain the state of fats with high content of unsaturated fatty acids at room temperature
b) state what living organisms always produces unsaturated fats
a)
- liquid at room temperature, lower melting point
- because fatty acid chain bends at double bonds, preventing fat molecules from aligning closely with one another.
b)
- plants (expect tropical oils like palm/coconut oil)
describe the composition of one molecule of triglyceride, and hence the condensation reaction in lipids
- one molecule of triglyceride consists of 3 fatty acid molecules and one molecule of glycerol
- each hydroxyl group (-OH) in the glycerol molecule reacts with the carboxyl group (-COOH) of a fatty acid. in this reaction, one molecule of water is removed and an ester bond is formed between glycerol and one fatty acid
what are the functions of lipids? (7 points)
- triglyceride serves as a form of storage of energy (higher energy value and harder to hydrolyse as compared with starch / glycogen -> long term storage)
- good thermal insulator to prevent excessive heat loss
- shock absorbant and protects delicate organs from mechnical shock
- releases metabolic water when hydrolysed
- low density substance that improves buoyancy of organisms
- major component of cell membrane
- electrical insulation and act as a component of myelin sheath surrounding nerve cells
describe the test for lipids
1) add 2cm3 of ethanol to two drops of the test substance in a test tube. mix well.
OR grind the solid test substance and add..(same).. allow any solid particles to settle
2) decant the ethanol into another test tube containing 2cm3 of water
3) mix well and observe for cloudiness
expected results (standard):
homogeneous solution formed when ethanol was added
lipids absent: solution remained homogeneous when water was added
lipids present: white emulsion was formed when water was added
draw the condensation / hydrolysis reaction of triglyceride
draw a saturated and unsaturated fatty acid
