Lipids Flashcards
What are lipids?
A group of substances that are soluble in alcohol rather than water. They include triglycerides, phospholipids, glycolipids and cholesterol.
What are the roles of lipids?
- Contains lots of energy
- Long-term energy stores
- Can be broken down quickly
- Acts as insulation
- Provides buoyancy
- Physical protection e.g. cushioning
- Waterproofing
- A source of water
What are macromolecules?
Macromolecules- a very large, organic molecule
What are Phospholipids?
Phospholipid- a molecule consisting of glycerol, two fatty acids and one phosphate group.
They are found in cell membranes.
Phosphates are ionise so phospholipids attracts water.
What are Triglycerides?
Triglycerides are made up of 1 glycerol and 3 fatty acids.
They are formed by condensation reactions and are broken by hydrolysis.
It forms ester bonds.
What are the functions of Triglycerides?
They are an energy source- Triglycerides can be broken down in respiration to release energy and generate ATP.
They are an energy store- because they are insoluble in water.
They are insulators for example Adipose tissue (blubber) is a storage location for lipids in whales acting as a heat insulator.
Buoyancy- because fat is less dense than water, it is used by aquatic mammals to help them stay afloat.
Protection- Humans have fat around delicate organs, such as their kidneys, to act as a shock absorber. The peptidoglycan cell wall of some bacteria is covered in a lipid-rich outer coat.
What is Glycerol?
Glycerol has three carbon atoms.
It is an alcohol, which means that it has free -OH groups.
What are fatty acids?
Fatty acids have a carboxyl group (-COOH), attached to a hydrocarbon tail, made of only carbon and hydrogen atoms.
The carboxyl group ionises into H+ and a -C00- group. This structure is therefore an acid because it can produce free H+ ions.
If a fatty acid is saturated this means that there are no C=C bonds in the molecule. If a fatty acid is unsaturated, there is a double bond between the two of the carbon atoms instead, which means they have fewer hydrogen atoms can be bonded to the molecule.
A single C=C bond makes a fatty acid monounsaturated. More than one C=C bond makes it polyunsaturated.
Having one or more C=C bond changes the shape of the hydrocarbon chain.
What are Ester bonds?
In Condensation reactions, when a water molecule is produced. They formed a type of covalent bond called an ester bond/
What is the structure of a phospholipid?
They have the same structure as Triglycerides, except that one of the fatty acids is replaced by a phosphate group. So the overall structure is 1 glycerol, 2 fatty acids and 1 phosphate group.
A condensation reaction between an OH group on a phosphoric acid molecule (H3PO4) and one of the three -OH groups on the glycerol forms an ester bond.
They have an even number of carbon atoms (usually 16 or 18).
One of the chains is saturated the other is unsaturated.
How do Phospholipids behave in water?
When surrounded by water, the phosphate group has a negative charge, making it polar. However, the fatty acid tails are non-polar and so are repelled by water.
Hydrophilic head- attracts water
Hydrophobic tail- repels water
This makes the phospholipid molecule amphipathic.
They may form a layer on the surface of the water with heads in the water and tails ticking 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.
What is the Phospholipid Bilayer?
Amphipathic phospholipids are excellent at forming membranes around the cells and organelles.
Cell membranes are surrounded by an aqueous solution.
The phospholipids form a bilayer, with two rows of phospholipids, tails pointing inwards and heads pointing outwards into the solution.
The individual phospholipids are free to move around in their layer, but will not move into any position where their hydrophobic tails are exposed to water. This gives the membrane more stability.
The membrane is selectively permeable. It is only possible for small and non-polar molecules to more through the tails in the bilayer, such as oxygen and carbon dioxide.
What is Cholesterol?
Is a steroid alcohol.
It is not made from glycerol or fatty acids. It consists of four carbon-based rings or isoprene units.
Cholesterol is a small and hydrophobic molecule.
It regulates the fluidity of the membrane, preventing it from becoming too fluid or stiff.
Cholesterol is usually made in the liver of animals.
Plants also have a cholesterol derivative in their membranes. It is called stigmasterol and is different from cholesterol in only one way- it has a double bond between carbon 22 and carbon 23.
Testosterone, oestrogen and Vitamin D are all made from Cholesterol
