lipids Flashcards
What are lipids? Are they soluble or insoluble?
A diverse group of compounds that are insoluble in water but soluble in organic solvents
what are the elements in lipids? proportion?
contain CHO, but proportion of oxygen is much less compared to carbohydrates
what are the 3 classes of lipids
triglycerides (fats/oils), phospholipids and steroids
test for presence of lipids and observation
emulsion test:
1. add 2cm3 of sample solution into test tube containing 2cm3 of ethanol
2. shake mixture well
3. allow mixture to settle for 2 minutes (for any lipids present in sample to dissolve in ethanol)
4. empty any clear liquid into a test tube containing 2cm3 of distilled water
observation:
lipids are present when white emulsion is formed
general formula of glycerol
C3H8O3
- 3 carbon atom
- 3 hydroxyl group
- 5 hydrogen atom
is glycerol soluble in water? why?
- glycerol is a polar hydrophilic molecule which is soluble in water
- this is due to the presence of -OH group in glycerol, which can form HB with water
general formula of fatty acid
R.COOH
- R is a long hydrocarbon chain consisting of a chain of carbon and hydrogen atoms
is fatty acid soluble in water? why?
- fatty acids are non-polar, hydrophobic molecules which are insoluble in water
- this is due to the presence of their non-polar hydrophobic hydrocarbon chain which is unable to form HB with water
why does unsaturated fatty acids have lower melting point than saturated fatty acids
- the C=C bonds in unsaturated fatty acid causes kinks in their fatty acid tails.
- this does not allow the unsaturated fatty acids to pack closely together, resulting in weaker hydrophobic interactions existing between fatty acid molecules.
- thus less heat/energy is required to disrupt these hydrophobic interactions to bring about a change in state. therefore, unsaturated f.a have a lower melting point that saturated f.a
what does a molecule of triglceride consists of
1 glycerol and 3 fatty acids
what bond is formed in a triglyceride
ester bond
formation of ester bond
in a condensation reaction known as esterification, one water molecule is removed when one of glycerol’s hydroxyl groups condense with the carboxyl group of a fatty acid, resulting in formation of a covalent bond known as ester bond
reverse process of esterification
saponification
describe the structure and functions of triglycerides (5)
- GOOD ENERGY SOURCE
- there is higher proportion of hydrogen and an almost insignificant proportion
of oxygen in lipids (triglycerides) compared to carbohydrates OR Lipids (triglycerides) have a higher ratio of energy-storing C-H bonds to carbon atoms
than carbohydrates
- therefore, more than twice the amount of energy in the form of ATP is released from the oxidation of a given mass of lipids compared to an equal mass of carbohydrates, hence lipids are a good energy source - GOOD ENERGY STORAGE
- lipids (triglycerides) contain more energy/gram than carbohydrates which
provide a more weight-efficient means for animals to store energy, thus lipids
are good energy storage molecules
- this is useful for animals where locomotion requires mass to be kept to a minimum - SOURCE OF METABOLIC WATER
- there is higher proportion of hydrogen in lipids (triglycerides) compared to carbohydrates
- during aerobic respiration, the completion oxidation of lipids (triglycerides) produces a larger amt of metabolic water/gram of lipid compared to the
oxidation of an equal mass of carbohydrates
- metabolic water is retained within the bodies of desert animals, helping them to survive when there is no liquid water for drinking - THERMAL INSULATION
- lipids (triglycerides) are good thermal insulators as they conduct heat slowly,
thus reducing heat loss from the body. This is important for animals living in
cold climates, as the thick subcutaneous layer of fats reduces the loss of body heat from the deeper regions of
the body to the surroundings - BUOYANCY
- Lipids (triglycerides) are less dense than water, and this is important for providing aquatic mammals with buoyancy
what does a molecule of phospholipid molecule consist of?
- a glycerol backbone
- a hydrophilic negatively charged phosphate group
- 2 non-polar hydrophobic fatty acid tails/hydrocarbon chains
