lipids Flashcards
two forms of lipid
triglycerides and phospholipids
how are triglycerides formed
condensation reaction of one molecule of glycerol and three molecules of fatty acid
lipid bond
condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond
fatty acids
contain a carboxylic acid group - connected to a hydrocarbon chain
R group may be saturated or unsaturated
saturated fatty acid
there are only single bonds between carbon atoms in the hydrocarbon chain
solid at room temperature
unsaturated fatty acid
one or more double bonds or triple bonds between carbon atoms in hydrocarbon chain
liquid at room temp
why are lipids not polymers
biological polymers have one kind of monomer that is repeated
lipids are not polymers because they are made of 2 types of monomer
phospholipids
one of the fatty acids of a triglyceride is substituted by a phosphate-containing group
polar (head) and non-polar (tail) - tails point together
glycerol + 2 fatty acids + phosphate group
comparing triglycerides and phospholipids
similarities
- both have fatty acids
- both have glycerol
- both contain ester bonds
differences
- TG 3FA, PL 2FA
- TG have no P group, PL have 1 P group
- TG non-polar, PL polar head and non-polar FA/hc tails
- TG insoluble in water, PL form monolayer/bilayer with head towards water and tails pointing away
- TG used as energy store, PL used to make membranes
test for lipids
(Crush the sample if it is a solid.)
Dissolve the sample in ethanol.
Add it to cold water.
Result: If lipid is present, an emulsion is formed. If lipid is not present, no emulsion is formed.
functions of lipids
• Triglycerides are long-term energy store in animals and plant seeds
• Compared to carbs, fat stores more energy per gram
• BUT more difficult to access / takes more O2 to respire it and release its energy
• Phospholipids: Cell membrane
• Less dense: efficient storage of energy in seeds
• Waxy cuticle (waterproofing) on leaves to reduce water-loss
• Thermal insulation: sub-cutaneous fat (adipose tissue)
• Electrical insulation (neurones are surrounded by insulating MYELIN sheath)
• Buoyancy eg. squaline that fills a shark’s liver
• Oils to protect and condition hair and skin produced by sebaceous glands
• Lubricant fluid between bones: synovial fluid contains a small quantity of lipids.
• Protection of delicate organs against mechanical injury
• Steroids: can act as hormones. Eg. Testosterone, Estrogen, etc
lipids
have many uses, including the bilayer of plasma membranes, certain hormones and as respiratory substrates
relate the structure of triglycerides to their functions
high energy:mass ratio - high calorific value from oxidation
insoluble hydrocarbon chain - no effect on water potential of cells and used for waterproofing
slow conductor of heat - thermal insulation
less dense than water - buoyancy of aquatic animals
compare phospholipids and triglycerides
both have glycerol backbone
both may be attached to a mixture of saturated and unsaturated fatty acids
both contain C, H, O
both formed by condensation reactions
contrast phospholipids and triglycerides
phospholipid
2 FA and 1 P group attached
hydrophilic head and hydrophobic tail
used primarily in membrane formation
triglycerides
3 FA attached
entire molecule is hydrophobic
used primarily as storage molecule
