1A - Lipids Flashcards
What 3 elements do lipids contain?
Hydrogen, carbon and oxygen.
How do the amounts of each element vary in lipids compared to carbohydrates?
The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates.
Are lipids soluble or insoluble?
Insoluble in water.
Soluble in organic solvents such as alcohols and acetone.
What are the 2 main groups of lipids?
Triglycerides (fats and oils) and phospholipids.
What are the main roles of lipids?
- Used in cell membranes.
- They are a source of energy.
- They are useful for waterproofing.
- Insulation.
- Protection.
How are lipids used in cell membranes?
Phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them.
How are lipids a source of energy?
When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water.
How are lipids used in waterproofing?
Lipids are insoluble in water and therefore useful as a waterproofing. Both plants and insects have waxy, lipid cuticles that conserve water, while mammals produce an oily secretion from the sebaceous glands in the skin.
How are lipids used in insulation?
Fats are slow conductors of heat and when stored beneath the body surface help to retain body heat. They also act as electrical insulators in the myelin sheath around nerve cells.
How are lipids used in protection?
Fat is often stored around delicate organs, such as the kidney.
What is the main difference between fats and oils?
Fats are solid at room temperature (10-20 degrees C) whereas oils are liquid.
What are triglycerides?
Three fatty acids combined with a glycerol.
What type of bond combines fatty acids and glycerol?
An ester bond.
How is glycerol made and broken down?
Through a condensation reaction forming an ester bond then through a hydrolysis reaction which breaks this.
What does the differences in the properties of different fats and oils come from?
Variations in the fatty acids.
How many different fatty acids are there?
Over 70.
What do all fatty acids have?
A carboxyl group (-COOH) with a hydrocarbon chain attached.
What does it mean if a fatty acid is saturated and why?
There are no carbon-carbon double bonds in the hydrocarbon chain because all of the carbon are linked to the maximum possible number of hydrogen atoms (4). They are saturated with hydrogen atoms.
What does it mean if a fatty acid is mono-unsaturated and why?
There is a single double bond between carbon atoms in the hydrocarbon tail.
What does it mean if a fatty acid is poly-unsaturated and why?
There is there is more than one double bond between carbon atoms in the hydrocarbon tail.
What is the structure/benefits of triglycerides?
- High ratio of energy-storing carbon-hydrogen bonds to carbon atoms.
- Low mass to energy ratio.
- Large, non-polar and insoluble in water.
- High ratio of hydrogen to oxygen atoms and so release water when oxidised.
How does triglycerides having a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms help their function?
This means that they are an excellent source of energy.
How does triglycerides having a low mass to energy ratio help their function?
It makes them good storage molecules because much energy can be stored in a small volume. This is especially beneficial to animals as it reduces the mass they have to carry as they move around.
How does triglycerides being large, non-polar and insoluble in water help their function?
This means that their storage does not affect osmosis in cells or the water potential of them.
How does triglycerides having a high ratio of hydrogen to oxygen atoms and so release water when oxidised help their function?
This release of water provides an important source of water, especially for organisms living in dry deserts.
Describe the shape/build of a phospholipid:
Similar to lipids except that one of the fatty acid molecules is replaced by a phosphate molecule.
They are made up of two parts: a hydrophilic ‘head’ which interacts with water but not with fat and a hydrophobic tail which orients itself away from water but mixes readily with fat.
Do fatty acid molecules attract or repel water?
Repel water (hydrophobic).
Do phosphate molecules attract or repel water?
Attract water (hydrophilic).
What does hydrophobic mean?
Repel water.
What does hydrophilic mean?
Attract water.
What does it mean if a molecule is polar?
The molecule has two ends (poles) that behave differently in response to water for example.
What happens when a polar phosphate molecule is placed in water?
It will position itself so that its hydrophilic head is as close to the water as possible and the hydrophobic tails are as far away from the water as possible.
What is the structure of phospholipids?
- Polar molecules (hydrophilic phosphate head and hydrophobic tail of 2 fatty acids).
- Hydrophilic phosphate ‘heads’ made of phospholipid molecules.
How does phospholipids being polar help their function?
In aqueous environments, phospholipid molecules form a bilayer within cell-surface membranes. As a result, a hydrophobic barrier is formed between the inside and the outside of a cell.
How does phospholipids having hydrophilic phosphate ‘heads’ made of phospholipid molecules help their function?
They help to hold at the surface of the cell-surface membrane.
How does phospholipids structure in general help their function?
It allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane. These glycolipids are important in cell recognition.
What is the test for lipids?
Emulsion test.
What is a positive result in the emulsion test?
A cloudy-white colour (emulsion).
How do you carry out the emulsion test?
- Take a completely dry and grease-free test tube.
- To 2cm3 of the sample being tested, add 5cm3 of ethanol.
- Shake the tube thoroughly to dissolve any lipid in the sample.
- Add 5cm3 of water and shake gently.
- A cloudy-white colour indicates the presence of a lipid.
- As a control, repeat the procedures using water instead of the sample; the final solution should remain clear.
What is the cloudy colour in the emulsion test due to?
Due to any lipid in the sample being finely dispersed in the water to form an emulsion. Light passing through this emulsion is refracted as it passes from oil droplets to water droplets, making it appear cloudy.
