Lipids Flashcards
What three elements do lipids contain
Carbon, oxygen and hydrogen
How does the proportion of oxygen to carbon and hydrogen in lipids compare to in carbohydrates
It is smaller in lipids than in carbohydrates.
What are the two main groups of lipids
Triglycerides and phospholipids.
Summarise how soluble lipids are
Insoluble in water but soluble in organic solvents such as alcohols and acetone.
List the five key roles of lipids
1) Cell membranes
2) Source of energy
3) Waterproofing
4) Insulation
5) Protection
Describe the role of lipids in cell membranes
Lipids are used in both cell-surface membranes and membranes around organelles.
Phospholipids contribute to the flexibility of membranes and the transport of lipid soluble substances across them.
Describe the role of lipids as a source of energy
When oxidised, lipids provide over twice the amount of energy as the same mass of carbohydrate and release valuable water.
Describe the role of lipids as waterproofing
Lipids are insoluble in water to they are useful as waterproofing.
Plants and insects have waxy lipid cuticles that conserve water.
Mammals produce an oily secretion from the sebaceous glands in the skin.
Describe the role of lipids as insulation
Fats are slow conductors of heat so when stored beneath the body surface help to retain body heat.
They also act as electrical insulators in the myelin sheath around nerve cells.
Describe the role of lipids as protection
Fat is often stored around delicate organs such as the kidney for extra protection.
What is the difference between fats and oils
Fats are solids at room temperature (10-20 degrees Celsius) whereas oils are liquids.
Describe the structure of a triglyceride
- Triglycerides have three fatty acids combined with glycerol.
- Each fatty acid forms an ester bond with glycerol in a condensation reaction.
- As the glycerol molecule in all triglycerides is the same, the differences in properties come from the fatty acids.
- There are over 70 different fatty acids and each contain the carboxyl (-COOH) group with a hydrocarbon chain attached.
- If the hydrocarbon contains no double bonds, then the triglyceride is saturated.
- If the carbon chain contains one double bond, the triglyceride is mono-unsaturated
- If the carbons chain contains multiple double bonds, then the triglyceride is polyunsaturated.
What is a saturated triglyceride
A triglyceride that contains no double carbon bonds within its carbon chains (found in the fatty acids molecules)
What is a mono-unsaturated triglyceride
A triglyceride that contains one double carbon bond in its carbons chains (found in the fatty acid molecules)
What is a polyunsaturated triglyceride
A triglyceride that contains multiple double carbon bonds within its carbon chains (found in the fatty acid molecules)
Describe how the structure of triglycerides relates to their properties
- Triglycerides have a high ratio of energy storing carbon-hydrogen bonds to carbon atoms and are therefore an excellent source of energy.
- Triglycerides have low mass to energy ratio which makes them good storage molecules as a lot of 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.
- Being large, non-polar molecules, triglycerides are insoluble in water. As a result, their storage does not affect osmosis in cells or the water potential of them.
- As they have a high ratio of hydrogen to oxygen atoms, triglycerides release water when oxidised and therefore provide an important source of water, especially for organisms living in dry deserts.
Describe the structure of phospholipids
-Phospholipids consist of one glycerol, two fatty acids and a phosphate group.
- Whereas fatty acid molecules repel water (are hydrophobic), phosphate molecules attract water (are hydrophilic).
- This means that phospholipids are made up of two parts- a hydrophilic ‘head’ that interacts with water (is attracted to it) but not fat and a hydrophobic ‘tail’ that orients itself away from water but mixes readily with fat.
- This makes phospholipids polar as they have two different ends that behave in different ways.
What does hydrolysis of a triglyceride produce
Three fatty acids and a glycerol
Describe how the structure of phospholipids relates to their properties
- Phospholipids are polar molecules (having a hydrophilic phosphate head and hydrophobic tail of two fatty acids). This means that in an aqueous environment 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.
- The hydrophilic phosphate heads of phospholipid molecules help to hold at the surface of the cell-surface membrane.
- The phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell surface membrane. These glycolipids are important in cell recognition.
