lipids Flashcards
(18 cards)
characteristics of lipids
- contains carbon, hydrogen and oxygen
- contain large proportion of hydrocarbons and a smaller proportion of oxygen than in carbohydrates
- due to hydrocarbon chains, lipids are mostly non-polar and hence, insoluble in water but soluble in organic solvents like ethanol
three types of lipids
triglycerides, phospholipids and steroids (cholesterol)
basic structure of triglycerides
one molecule of glycerol + three fatty acids attached via ester linkages
what are fatty acids made up of?
consists of a long hydrocarbon chain that varies in length + and a terminal carboxyl group
two types of fatty acids
saturated fatty acids only consists of carbon-carbon single bonds
unsaturated fatty acids have one (monounsaturated) or more (polyunsaturated) carbon-carbon double bonds which causes the chain to kink.
relationship between melting point of FA and the length of hydrocarbon tail
longer hydrocarbon chains of fatty acids have more hydrophobic interactions, and more heat is required to disrupt these hydrophobic interactions, resulting in higher MP due to longer hydrocarbon chains
relationship between MP of FA and number of carbon-carbon double bonds
with more C=C double bonds, there are greater kinks in the hydrocarbon chain. this causes the FA to be less closely packed, resulting in lesser hydrophobic interactions, less heat required to disrupt these hydrophobic interactions, resulting in lower MP
relationship between water solubility of FAs and length of hydrocarbon tail
short FAs are soluble in water as the carboxyl group is normally ironsides under physiological conditions, forming a charged COO- group that interacts with water. however, as the length of the hydrocarbon chain increases, water solubility decreases due to the non-polar hydrophobic nature of the hydrocarbon chain
glycerol
an alcohol which has 3 carbons that each bear a hydroxyl group, making it polar and allowing it to form hydrogen bonds with water, hence making it soluble in water
how are triglycerides formed
formed from a condensation reaction between glycerol and three fatty acid chains. each hydroxyl group in glycerol reacts with the carboxyl group of a FA molecule to form an ester linkage, removing a water molecule in the process. hence, 3 ester linkages are formed with the removal of 3 water molecules
why are lipids not considered as polymers
they do not consist of long, repeating chains of monomers and are instead composed of different components which are mainly FAs and glycerol
structure and properties of triglycerides, in relation to their functions (energy storage in relation to carbon, hydrogen and oxygen atoms)
- triglycerides are highly reduced, with a high ratio of C-H bonds to carbon atoms, making them a good source of energy as they supply many hydrogens for reduction of NAD
- triglycerides have lower mass per unit volume due to high ratio of hydrogen to oxygen atoms compared to carbohydrates. they serve as good energy storage because more energy can be stored in a small volume. they release twice as much energy in their form of ATP compared to an equivalent mass of carbohydrates . this benefits animals, as it reduces the mass they have to carry when moving around. this also makes them less dense than water, improving buoyancy in mammals. they also release metabolic water when oxidases and provides an important source of water especially for organisms living in dry deserts.
structure and properties of triglycerides, in relation to their functions (solubility and conductivity of heat)
- they are non-polar and hence insoluble in water. they serve as good energy storage molecules as they do not affect the WP of cells. it also repels water and prevents excessive evaporation of water from terrestrial animals.
- they are poor conductors of heat as unlike ionic and metallic bonds, hydrophobic interactions impede transmission of heat energy. this is seen as blubber in the skin of arctic animals slows down the rate of heat transfer, helping to maintain a stable internal temperature, protecting the body from heat loss.
functions of triglycerides as adipose tissue
triglycerides are stored in fat cells which are part of the fat tissues (adipose tissues) found in the body. as adipose tissue are soft pliable structures, they can absorb mechanical shock and protect the internal organs from injury, indirectly contributing to the physical cushioning of mechanical shock.
structure and formation of phospholipids
they consist of a glycerol linked to a phosphate group and two FAs. the phosphate group may be bonded to a small organic molecule that is charged or polar. during formation, the two FAs are linked to the glycerol by 2 ester bonds while the phosphate group is linked to the glycerol by phosphoester bonds through condensation reactions.
properties of phospholipids
they are amphipathic in nature, made up of a hydrophilic phosphate group and hydrophobic hydrocarbon tails. when placed in water, phospholipids can self-assemble in aggregates (micelles and bilayers that shield their hydrophobic tails away from water)
functions of phospholipids
- amphipathic - forms bilayer in aq. env. which serves as hydrophobic barrier between inside and outside allowing for compartmentalisation
- double bond in HC chains forming a kink - reduces hydrophobic interactions between phospholipids giving greater fluidity to membrane
- forms glycolipids - cell recognition and adhesion, and act as receptors for signal molecules
emulsion test for lipids
shake food sample with ethanol, decant into water
presence of lipids has white emulsion after decanting
