Lipids Flashcards
Describe lipids
A diverse group of compounds which all contain carbon, hydrogen and oxygen
Characteristics of lipids
- insoluble in water
* soluble in other lipids and organic solvent (e.g. ethanol, chloromethane, diethyl ether)
Describe the composition of lipids
Larger number of carbon and hydrogen atoms than oxygen atoms
Significance??
Describe triglycerides
- lipids made from one molecule of glycerol and 3 fatty acid molecules
- these molecules are not identical and are therefore not monomers; lipids are not polymers
- AKA: triacylglycerols, true fats, neutral fats
Describe glycerol
An alcohol containing 3 carbon atoms each linked to a hydroxyl group
Describe a fatty acid
- long chain of carbon and hydrogen atoms (a hydrocarbon chain) ending in an acidic carboxyl (-COOH) group
- (-COOH) ionises in water to release a hydrogen ion (proton), which gives fatty acids their acidic properties
- -COOH -COO- + H+
Describe the formation of triglycerides
- each hydroxyl group on the glycerol molecule combines with a carboxyl group on a fatty acid molecule
- condensation reaction (water is released)
- an ester bond is formed
Describe fats
- solid at RT (20°C)
- found in animals
- saturated fats
Describe oils
- liquid at RT
- found in plants
- unsaturated fats
Describe saturated fatty acids
- each carbon atom in the hydrogen carbon is linked to a carbon atom on each side and 2 hydrogen atoms
- the carbons are bonded to the maximum number of other atoms
- only contain single bonds in the hydrocarbon chain; the chain is relatively straight; triglycerides can pack closely together; solid at RT
Describe unsaturated fatty acids
- the carbon atoms in the hydrocarbon chain are not bonded to the maximum number of other atoms
- two or more carbon atoms have a double bond between them
Define monounsaturated fatty acids
Fatty acids with one double bond
Define polyunsaturated fatty acids
Fatty acids with two or more double bonds
Describe cis double bonds
- both CH2 groups are on top; causes a kink in the hydrocarbon chain
- prevents molecules from packing closely
- triglycerides with a high proportion are oils because attraction between molecules is weak
Describe trans double bonds
- similar properties to saturated fatty acids; solid (straighter chain)
- vv unhealthy
What is adipose tissue
Excess fat in mammals, laid down for storage in special connective tissue
How do lipids compare to carbs and proteins?
- triglycerides have a higher proportion of hydrogen compared to carbohydrates or proteins
- they are a more concentrated source of energy
- each gram yield about 38kJ (more than double that of a gram of carbohydrate)
How are lipids adapted for heat insulation?
- fat is a bad conductor of heat
* mammals increase adipose tissue in winter to reduce heat loss
How are lipids adapted for shock absorption
• thick layers of adipose tissues are formed around delicate mammalian organs (e.g. kidneys) to stop them from being vulnerable to knocks and bumps
How are lipids adapted for buoyancy
Many single-celled aquatic organisms produce an oil droplet to aid buoyancy
Describe the composition of a phospholipid
- a molecule of glycerol attached to 2 fatty acid chains
- the third hydroxyl group of glycerol combines with phosphoric acid to form a polar phosphate group
- amphipathic -> one end of the molecule is hydrophilic (the head), and the other is hydrophobic (the tail)
Why is the tail of a phospholipid hydrophobic
- the tail is the fatty acid chains
* these are oily
Describe the phospholipid bilayer
- in water, phospholipid molecules collect together into a single (monomolecular) layer
- the hydrophilic heads poke into the water
- hydrophobic rails point inwards, away from watery environment
- gives cell membranes their fluid properties; allows lipid-soluble substances to pass easily though them
Why does the phospholipid bilayer form
because, in cells, both the intracellular and immediate external environment are watery
Describe waxes
- similar to triglycerides
- contain fatty acids joined to long-chain alcohols rather than glycerol
- usually relatively hard solids at room temperature
- provide protection and waterproofing on TBR surfaces of insects and leaves
Describe steroids
- contain four rings of carbon and hydrogen atoms with various side chains
- many animal hormones are steroids (e.g. oestrogen, testosterone) -> made from cholesterol
Describe cholesterol
- Raw material for the manufacture of vitamin D
* viral component in mammalian cell membranes; strengthens them at high temperatures
