Lipids 3.1.3 Flashcards
Are lipids soluble or insoluble in water
Insoluble
Are lipids polar or nonpolar
Non-polar
Describe four characteristics of lipids
*They contain carbon, hydrogen and oxygen
The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates.
*They are insoluble in water
*They are soluble in organic solvents E.G. acetone, alcohols.
Name the four roles of lipids
Source of energy
Waterproofing
Insulation
Protection
How do lipids provide a source of energy
When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water (metabolic water).
How to lipids waterproof
As lipids are insoluble in water, it is therefore useful for waterproofing, E.G. both plants and insects have waxy cuticles is that reduce water loss (conserving it), while the mammals produce an oily secretion from the sebaceous glands in the skin
How do lipids provide insulation
Facts are slow conductors of heat and when stored beneath the body surface, help to retain body heat. They also act as electrical insulators E.G.the myelin sheath around nerve cells
How do lipids provide protection
Fat is often stored around delicate organs, E.G.kidneys.
How is a triglyceride molecule formed
It is formed by three condensation reactions between the three hydroxyl groups in the glycerol and the three fatty acid chains. This creates a triglyceride and three water molecules
How do triglycerides differ from one another
The glycerol molecule stays the same in all triglycerides. The differences in the properties of the different facts and oils come from variations in the fatty acids
What part of the fatty acid chains are polar and which are non polar
The hydrocarbon chains are nonpolar, but the carboxyl groups are polar.
Define mono-unsaturated fatty acid
If it has one single double carbon bond
Define Polyunsaturated fatty acid
If it has more than one double carbon bond
How is the structure of triglycerides related to its properties
- Triglycerides have a high ratio of energy store and carbon hydrogen bonds to carbon atoms, so are an excellent source of energy.
- Triglycerides have a low mass to energy ratio, making them good storage molecules because lots of energy can be stored in a small volume. This is extremely beneficial to animals as it reduces the mass they have to carry around.
- Being larger, nonpolar molecules, triglycerides are insoluble in water, so they do not affect the water potential or osmosis in cells.
- As they have a high ratio of hydrogen to oxygen atoms, they release water and oxidised and therefore provide an important source of water, especially for organisms living in dry deserts e.g. camels
What is a phospholipid
The phospholipid molecule is an ester composed of glycerol, two fatty acid chains and a polar group containing a phosphate group
What part of the phospholipid are hydrophilic and what parts are hydrophobic
The phosphate group is hydrophilic and soluble in water, but the fatty acid chains are hydrophobic and are not soluble in water. At air-water, or oil-water interfaces, the phospholipid molecule orientate themselves so that their heads are in water.
How does the phospholipid orientate itself in water
The hydrophilic heads are as close to the ward as possible and the hydrophilic tails are as far away from the water as possible
How does the structure of a phospholipid relate to its properties
- Phospholipids are polar molecules, having hydrophilic phospholipid head and hydrophobic tails of two fatty acids. This means that in an aqueous environment, phospholipid molecules from a bilayer within cell surface membranes. As a result, a hydrophobic barrier is formed between the inside and the outside of the cell.
- The hydrophilic phospholipid heads of the phospholipid molecules help to hold at the cell-surface membrane.
- The phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell surface membrane. These are important in cell recognition.
Name 5 differences between a triglycerides and phospholipids
*Triglycerides are lipids that are composed of a glycerol backbone attached to three fatty acid chains
Phospholipids are lipids composed of a phosphate group attached to a glycerol backbone
*Triglycerides have three fatty acid chains whereas phospholipids have three fatty acid chains
*Triglycerides have no phosphate group attached to the glycerol backbone whereas phospholipid have a phosphate group attached to the glycerol backbone
*In the formation of a triglyceride molecule, three water molecules are released whereas in the formation of a phospholipid molecule, to water molecules are released.
*Triglycerides act as fat storage in the body whereas phospholipid make up membranes in the cell.
Test for lipids (emulsion test)
1) Take a completely dry and grease-free test tube
2) Grind 2 cm³ of the sample and add 5 cm³ of ethanol
3) shake the tube starrily to dissolve any lipid in the sample
4) Add 5 cm³ of water and shake gently
5) A cloudy white colour indicates the presence of a lipid
6) As a control, repeat the method using water instead of the sample, the final solution should remain clear.
