Lipids Flashcards
what kind of energy do lipids store?
chemical energy
what is an emulsion?
An emulsion is when small droplets of a substance are suspended in another solution.
what are triglycerides?
A type of lipid mainly used as energy storage molecules
How are triglycerides formed?
Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid.
Ester bonds form between the glycerol hydroxyl group and the fatty acid carboxyl group.
One water molecule is released per ester bond.
What is the structure of fatty acids?
They have long ‘tails’ made of a chain of hydrocarbons with 4-36 carbon atoms
Glycerol links to the central carbon atom on fatty acids
What are the two types of fatty acids?
Saturated
Unsaturated
What is the difference between a saturated an an unsaturated fatty acid?
A saturated fatty acid is fully “saturated” with hydrogens along the carbon skeleton hence involving only single bonds.
An unsaturated fatty acid can contain one or more double bonds between the carbon atoms having less hydrogens bonded to the carbon skeleton.
Where is the chemical energy in triglycerides stored?
Chemical energy is stored in the fatty acid hydrocarbon tails
The long hydrocarbon chains contain many carbon- hydrogen bonds with little oxygen (triglycerides are highly reduced)
So when triglycerides are oxidised during cellular respiration this causes these bonds to break releasing energy used to produce ATP- also releases large numbers of water molecules (metabolic water)
What is the behaviour of triglycerides around water?
Triglycerides are insoluble in water.
Their fatty acid tails are hydrophobic. As a result they do not cause osmotic water uptake and the cells water potential is not affected.
In cells, the insoluble triglycerides crowd together as droplets because the hydrophobic fatty acid tails face inwards.
what is the difference between an unsaturated fatty acid which is mono or poly- unsaturated?
Mono- 1 double bond
Poly- 1 + double bond
If H atoms are on the same side of the double bon they are cis-fatty acids and are metabolised by enzymes
If H atoms are on opposite sides of the double bond they are trans- fatty acids and cannot form enzyme-substrate complexes, therefore are not metabolised. They are linked with coronary heart disease
The presence of double bonds causes the molecule to link or bend and they therefore cannot pack so closely together
This makes them liquid at room temperature rather than solid, and they are therefore describes as oils rather than fats
what is the structure of a phospholipids?
A phospholipid consists of 2 fatty acid molecules bonded to a glycerol molecule which is bonded to a phosphate ion
what is the polarity of a phospholipid?
The phosphate ion is polar - soluble in water: hydrophilic
The fatty acid ‘tails’ are non-polar - insoluble in water: hydrophobic
hence phospholipids are amphipathic
- they can form mono layers or bilayers in water
what happens when a phospholipid bilayer is formed?
Due to the presence of hydrophobic fatty acid tails, a hydrophobic core is created when phospholipid bilayer forms.
How does the composition of phospholipids contribute to the fluidity of the cell membrane?
If there are mainly saturated fatty acid tails then the membrane will be less fluid
If there are mainly unsaturated fatty acid tails then the membrane will be more fluid
How are O2 and CO2 able to enter and exit cells through the phospholipid bilayer?
Unsaturated fatty acids in the phospholipids create gaps which make the cell-surface membrane flexible and allow some small molecules like CO2 and O2 to pass through.
