3. 1. 3 Lipids Flashcards
Give two groups of lipids.
Triglycerides and Phospholipids.
How are triglycerides formed?
Triglycerides are formed by the condensation reaction of one molecule of glycerol and three molecules of fatty acids.
Each fatty acid forms an ester bond with glycerol.
What does a condensation reaction between glycerol and fatty acid form?
A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond.
Is the R-group of a fatty acid unsaturated or saturated?
The R-group of a fatty acid may be unsaturated or saturated.
What happens in a phospholipid?
One of the fatty acids of a triglyceride is substituted by a phosphate-containing group.
What are the different properties of a triglyceride?
- Non-polar structure making them insoluble in water. Storage doesn’t affect osmosis in cells or water potential of them.
- Effective energy storage molecule as they can be stored in adipose tissue without attracting water.
- High ratio of energy storing carbon-hydrogen bonds to carbon atoms so are a good energy source.
- Low mass:energy making them good storage molecules, much energy can be stored in a small volume.
What are the properties of phospholipids?
- Polar molecule
- Formed by a hydrophilic phosphate head bonding with hydrophobic hydrocarbon (fatty acid) tails.
- Known as amphipathic because of this.
- Phosphate head is polar (hydrophilic) therefore soluble in water.
- Fatty acid tail is non-polar (hydrophobic) therefore insoluble in water.
- In (aq) environment, bilayer formed in cell surface membranes. As a result, hydrophobic barrier is formed between inside and outside of cell.
Describe the emulsion test for lipids.
- Add ethanol to the sample and vigorously shake for one minute
- Pour solution into a test tube with water.
- Any lipids present will float to the top and form a milky white emulsion.
During the emulsion test for lipids, what happens when there is a lot of lipids present?
The greater the concentration of lipids in your sample, the more apparent the milky colour will become.
What are the characteristics of lipids?
- Contain carbon, hydrogen and oxygen
- They are insoluble in water
- They are soluble in organic solvents
List the roles of lipids.
- Source of energy
- Waterproofing
- Insulation
- Protection
Why are lipids a good source of energy?
When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water.
Why are lipids used for waterproofing?
They are insoluble in water, therefore useful in waterproofing.
Give an example of plants and mammals using lipids for waterproofing.
- Plants and insects have waxy, lipid cuticles that conserve water.
- Mammals produce an oily secretion from the sebaceous glands in the skin.
How are glycolipids formed?
The phospholipid structure allows them to form glycolipids by combining them with carbohydrates within the cell surface membrane.
