Biological Molecules - Lipids Flashcards
What are lipids?
- Contain large amounts of carbon and hydrogen but smaller amounts of oxygen
- Not polar so are therefore insoluble in water as they do not attract water molecules
- Do dissolve in alcohol
- Not polymers but do have different components bonded together
- Macromolecules
What are the three most important lipids
- Triglycerides
- Phospholipids
- Steroids
Describe Triglycerides
- Made up of Glycerol and Fatty Acids
Describe Glycerol
- 3 carbon atoms, an alcohol with 3 OH groups attached to it, these are important to the structure of triglyceride
Describe fatty acids
- Have a carboxylic group -COOH attached to a hydrocarbon chain, this tail is made up of hydrogen and carbon atoms only
Fatty acids - what happens to the glycerol in a fatty acid which makes it acidic
- The carboxyl group ionises into H+ and -COO- group, this is therefore an acid as it produces free H+ ions
Name the two different types of fatty acid and what makes them different
- A single C=C bond makes a fatty acid monounsaturated, more than one C=C bond makes it polyunsaturated
Why is unsaturated fat better than saturated
- Having more than one C=C bond changes the hydrocarbon chain this gives it a kink where the double bond is, the kinks push the molecules apart making it more fluid and the melting point lower, this also makes it more healthy as there are less fatty acids present
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What are completely digested fatty acids called
essential fatty acids
What is the covalent bond between lipids called
An ester bond
How does a triglyceride form
- Triglyceride consist of one glycerol molecule bonded to three fatty acids, A condensation reaction happens between the COOH of the fatty acid and the OH group of the glycerol
- Because there are 3 OH groups three fatty acids will bond therefore it is called a triglyceride
- A condensation reaction happens and a water molecule will be produced and a covalent bond is formed this is known as ester bond
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What are the functions of Triglycerides
- Energy source
- Energy store
- Insulation
- Buoyance
- Protection
What are the functions of Triglycerides; Energy source
Triglycerides can be broken down in respiration to release energy and generate ATP, Hydrolyse the ester bonds then both the glycerol and the fatty acids can be broken down to carbon dioxide and water, respiration of a lipid produces more water than respiration of a sugar
What are the functions of Triglycerides: Energy store
Triglycerides are insoluble in water so can be stored without affecting the water potential of the cell, mammals store the fat in adipose cells under the skin, one gram of fat releases twice as much energy as 1g of glucose – this is because lipids have a high proportion of hydrogen atoms than carbohydrates and nearly no oxygen atoms
What are the functions of Triglycerides: Insulation
in whales adipose tissue is a storage location for lipids called blubber this acts as a heat insulator, Lipids in nerve cells act as an electrical insulator, when animals hibernate they eat and store extra fat
What are the functions of Triglycerides: Buoyance
because fat is less dense than water it is used by aquatic mammals to help them stay afloat
What are the functions of Triglycerides: Protection
fat is around delicate organs as a shock absorber, the peptidoglycan cell wall of some bacteria is covered in a lipid rich outer coat
What is the structure of Phospholipids
- Same structure as triglycerides except that one of the fatty acids is replaced by a phosphate group, A condensation reaction between an OH group on a phosphoric acid molecules and one of three -OH groups on the glycerol forms an ester bond
- Most of the fatty acids found in phospholipids have an even number of carbon atoms – commonly one of these chains is saturated and one of them unsaturated
How do phospholipids respond to water
- When in water the phosphate group has a negative charge making it polar and attracted to the water
- But the fatty acid tails are non-polar and are repelled by the water, therefore they have a hydrophobic and hydrophilic set up and the phospholipid molecules is amphipathic, membrane molecules tend to be amphipathic whereas those involved in storage are not
What are the properties of Amphipathic Phospholipids in water
they form a layer on the surface of the water with heads in the water and tails sticking up out of the water, they may also form micelles – tiny balls with the tails tucked away inside and the heads pointing outwards into the water
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How do phospholipids form a Bilayer
Phospholipids form a bilayer with two rows of phospholipids tails pointing inwards as they are hydrophilic and heads pointing outwards as they are hydrophobic
How do Phospholipids provide stability in a bilayer
- The individual phospholipids are free to move around in their layer but will not move to any position where the tail is exposed to the water therefore it provides the membrane with stability
Why does a bilayer have a selectively permeable membrane
- Membrane is also selectively permeable as its only possible for small nonpolar molecules to move throughout the tails of the bilayer like carbon dioxide and oxygen therefore the membrane can control what goes in and out of the cell keeping it functioning properly
What is cholesterol
- Steroid alcohol
- type of lipid which is not made from glycerol or fatty acids
- consists of four carbon based rings or isoprene units
What are the functions of cholesterol
- Small and hydrophobic molecule therefore can sit in the hydrophobic part of a bilayer
- Regulates the fluidity of the membrane so it does not become to stiff or fluid
- Mainly in the liver in animals, plants also have a cholesterol derivative in their membranes called stigmasterol – different from cholesterol as it has a double bond between carbon 22 and carbon 23
- Steroid hormones such as testosterone, oestrogen and vitamin D are all made from cholesterol – they are small and hydrophobic so can pass through the hydrophobic part of the cell membrane and any other membrane in the cell
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