Chapter 3- 3.5- Lipids Flashcards
Are lipids polar molecules (charged) ?
No
They are Non polar molecules as the electrons in the outer orbitals that form the bonds are more evenly distributed than in polar molecules.
This means there are no positive or negative areas within the molecules and for this reason lipids are not soluble in water.
That is why oil and water do not mix.
What type of molecule is a lipid ?
It is a complex molecule known as macromolecules.
Macromolecules are not built from repeating units or monomers like polysaccharides
What is a triglyceride made of ?
A triglyceride is made by combining 1 glycerol molecule with 3 fatty acids.
What group of molecules does glycerol belong to ?
Alcohols.
What group of molecules do fatty acids belong to ?
Carboxylic acids- they consist of a carbonyl group (-COOH) with a hydrocarbon chain attached.
What is esterification an example of ?
A condensation reaction.
Glycerol and fatty acids both contain hydroxyl (OH) groups. The hydroxyl groups interact, leading to the formation of three water molecules and bonds between the fatty acids and the glycerol molecule. These are called ester bonds and this reaction is esterification an example of a condensation reaction.
What are lipids commonly known as ?
Fats- lipids solid at room temp
Oils- lipids liquid at room temp
They are molecules containing carbon, hydrogen and oxygen.
What happens when triglycerides are broken down?
3 water molecules need to be supplied to reverse the reaction that formed the triglyceride. This is an example of a hydrolysis reaction.
What is the difference between saturated and unsaturated lipids?
Fatty acid chains that have no double bonds present between the carbon atoms are called saturated, because all the carbon atoms form the maximum number of bonds with hydrogen atoms.
A fatty acid with double bonds between some of the carbon atoms is called unsaturated. If there is just one double bond it is called monounsaturated. If there are two or more double bonds it is called polyunsaturated.
The presence of double bonds causes the molecule to kink and bend and they therefore cannot pack so closely together. This makes them liquid at room temperature rather than solid, and they are therefore described as oil rather than fats.
Plants contain unsaturated triglycerides, which normally occur as oils, and tend to be more healthy in human diet than saturated triglycerides, or (solid) fats.
There has been some evidence that in excess, saturated fats can lead to coronary heart disease, however the evidence remains inconclusive. An excess of any type of fat can lead to obesity, which also puts a strain on the heart.
What are phospholipids?
Phospholipids are modified triglycerides and contain the element phosphorus along with carbon, hydrogen, and oxygen.
Inorganic phosphate ions (PO(4)^3-) are found in the cytoplasm of every cell.
The phosphate ions have extra electrons and so are negatively charged, making them soluble in water.
One of the fatty aid chains in triglyceride molecule is replaced with a phosphate group to make a phospholipid.
Why are phospholipids called surfactants?
Due to their length, they have a non-polar end or tail (the fatty acid chains) and a charged end or head (the phosphate group). The non-polar tails are repelled by water (but mix readily with fat). They are hydrophobic.
The charged heads (often incorrectly called polar ends) will interact with, and are attracted to, water. They are hydrophilic.
As a result their dual hydrophobic/ hydrophilic structure, phospholipids behave in an interesting way when they interact with water.
They will form a layer on the surface of the water with the phosphate heads in the water and the fatty acid tails sticking out of the water. Because of this they are called surface active agents or surfactants for short.
Phospholipids can also form a two-layered sheet formation called what?
They can also form structures based on a two-layered sheet formation (a bilayer) with all of their hydrophobic tails pointing towards the centre of the sheet, protected from the water by the hydrophilic heads.
It is the result of this bilayer arrangement that phospholipids play a key role in forming cell membranes. They are able to separate an aqueous environment in which cells usually exist from the aqueous cytosol within cells. It is thought that this is how the first cells were formed and, later on, membrane-bound organelles within cells.
What are sterols?
Sterols are known as steroid alcohols, are another type of liquid found in cells. They are not fats or oils and have little in common with them structurally.
They are complex alcohol molecules, based on a four carbon ring structure with a hydroxyl (OH) group at one end.
Like phospholipids, however, they have dual hydrophilic/hydrophobic characteristics. The hydroxyl group is polar and therefore hydrophilic and the rest of the molecule is hydrophobic.
What is an example of a sterol?
Cholesterol is a sterol. The body manufactures cholesterol primarily in the liver and intestines. It has an important role in the formation of cell membranes, becoming positioned between the phospholipids with the hydroxyl group at the periphery of the membrane.
This adds stability to cell membranes and regulates their fluidity by keeping membranes fluid at low temperatures and stopping them becoming too fluid at high temperatures.
Vitamin D, steroid hormones, and bile are all manufactured using cholesterol.
What are the roles of lipids?
Due to their non-polar nature, lipids have many biological roles.
These include:
Membrane formation and the creation of hydrophobic barriers
Hormone production
Electrical insulation necessary for impulse transmission
Waterproofing, for example in birds’ feathers and on plant leaves.
