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List the functions of lipids in living organisms.
- Source of energy - can be respired
- Energy storage
- All biological membranes made from lipids
- Heat/electrical insulation - eg. blubber in whales, electrical insulation around nerve cells
- Protection - eg. cuticle on plant leaves protected from drying out
- Some hormones (steroid hormones) are lipids
Lipids contain which elements? Are they soluble in water?
- Carbon, hydrogen & oxygen. (oxygen small proportion)
- Lipids insoluble in water.
Lipids performing roles of energy supply and storage, as well as those in the membranes, contain what?
Glycerol and fatty acids
Glycerol and fatty acids - which is always the same and which can differ significantly?
- Glycerol molecule is always the same.
- Fatty acid molecules can differ significantly.
What are essential fatty acids? What is this similar to?
- Fatty acids that animals cannot make and therefore an essential part of their diet.
- Very much like essential amino acids.
Imagine the structure of glycerol.
Describe the structure of a fatty acid.
- An acid group at one end (same as amino acid)
- Rest of the molecule consists of a hydrocarbon chain (can be anything from 2-20 carbons)
What is a monounsaturated and polyunsaturated fatty acid?
- Monounsaturated - one C=C bond
- Polyunsaturated - more than one C=C bond
Why are unsaturated lipids often liquid (oil) at room temp, whereas saturated are fats?
C=C bonds changes the shape of the hydrocarbon chain (fatty chain), making the chain "kink" at the position of double bond, making the molecules in a lipid push apart, making them more fluid.
What does a triglyceride consist of?
Consists of one glycerol molecule bonded to three fatty acid molecule.
How do the fatty acid molecule bond to the glycerol molecule?
By condensation reaction between the acid group of the fatty acid and one of the OH (hydroxyl) groups of the glycerol molecule forms a covalent bond. (Water molecule is also produced).
What is the bond between the acid group of a fatty acid molecule and one of the OH groups of a glycerol molecule called? What is the molecule produced called at this point?
- Ester bond
- Produces a monoglyceride
- (two more condensation reactions with the other OH groups and two more fatty acid molecules will produce a triglyceride molecule).
Are triglycerides soluble in water? Why?
- They are insoluble in water. (hydrophobic)
- Because the charges on the molecule are evenly distributed around the molecule and thus it cannot form hydrogen bonds with the water molecules.
Imagine a triglyceride molecule
What is the difference between a triglyceride and a phospholipid?
- In phospholipids, the third fatty acid is not added to the glycerol molecule, and instead a phosphate group is covalently bonded to the third OH group by condensation.
- Phosphate head is hydrophilic and fatty acid tails are hydrophobic.
How can organisms control fluidity of membranes? (think phospholipids)
- The fatty acids can be saturated or unsaturated.
- An organism living in colder climates will have increased number of unsaturated fatty acids in their phospholipid molecules, making membrane more fluid because of the "kink" in their shape.
How does respiration from lipids happen? What are the advantages?
- First requires hydrolysis of the ester bonds
- Both the glycerol and the fatty acids can then be broken down completely into CO2 and H2O to release energy which is used to generate ATP.
- Advantages: respiration of one gram of lipid gives roughly twice as much as respiration of one gram of carbohydrate.
- They can be stored without affecting water potential for they are insoluble.
- Respiration of lipid gives out much more water than carbohydrate. (metabolic water vital for some organisms in extreme climates)
Describe the structure of a cholesterol molecule.
- It is a lipid, but not formed from fatty acids and glycerol.
- Small, narrow molecule made from 4 carbon-based rings.
Explain the functions of cholesterol.
- All biological molecules have cholesterol.
- Its small, narrow structure and hydrophobic nature allow it to sit between phospholipid hydrocarbon tails and help regulate fluidity and strength of membrane.
- Steroid hormones (eg. testosterone, oestrogen, vitamin D) are made from cholesterol. Its lipid nature allows it pass straight through phospholipid bilayer and nuclear envelope to reach target receptor.
How can cholesterol be a problem for humans?
- In bile, cholesterol can stick together to form lumps called gallstones.
- In blood, cholesterol can be deposited in inner lining and cause atherosclerosis.