3.5 Lipids Flashcards
What are lipids
Commonly known as fats and oils; are molecules containing carbon, hydrogen, oxygen.
Generally, oils are lipids that are liquid at room temp. and fats are lipids that are solid at room temp.
Non-polar molecules as the electrons in the outer orbitals that form the bonds are more evenly distributed than in polar molecules.
Therefore, no pos. or neg. areas in lipids and so aren’t soluble in water. Oil and water don’t mix.
Large molecules known as MACROMOLECULES which are built from repeating units or monomers (like polysaccharides).
What are Triglycerides
Made by combining ONE GLYCEROL with 3 FATTY ACIDS.
Member of alcohol group.
Fatty acids belong in group of CARBOXYL (-COOH) with a hydrocarbon attached.
The hydroxyl groups interact leading to 3 water molecules forming and bonds between the fatty acids and the glycerol molecule.
These bonds are called ESTER BONDS; reaction is ESTERIFICATION. (example of condensation reaction)
When triglycerides are broken down, 3 water molecules need to be supplied to reverse the reaction that formed the triglyceride (example of hydrolysis reaction).
What is the structure of saturated and non-saturated fatty acid chains
Fatty acid chains that have NO DOUBLE BONDS between carbon atoms are SATURATED, because all the carbon atoms form the max. number of bonds with hydrogen atoms (i.e. saturated with hydrogen atoms).
Fatty acid WITH DOUBLE BONDS between some carbon atoms are UNSATURATED. If there is one double bond, it’s MONOSATURATED. If there’s 2 or more then it’s POLYSATURATED.
The double bonds cause the molecule to bend/kink and so can’t be as compact. This makes them liquid at room temp.
Plants contain UNSATURATED TRIGLYCERIDES which normally occur as oils and tend to be healthier in our diets.
What are phospholipids
Modified triglycerides and contain phosphorous as well as C, O and H.
One of the 3 fatty acids is REPLACED with phosphate group to make it a phospholipid.
INORGANIC phosphate ions are found in the cytoplasm of every cell. The phosphate ions have extra electrons and so are neg. charged, making them soluble in water.
Phospholipids are unusual because, due to their length, they have a non-polar tail (fatty acid chains) and a charged head (phosphate group).
Non-polar tails are HYDROPHOBIC and the head are HYDROPHILIC.
As a result, they will from a layer on the surface of water with the heads in the water and the tails sticking out. Because of this they are called surface active agents or SURFACTANTS.
Also from the phospholipid bilayer in cell membranes; able to separate an aqueous environment in which cells usually exist from the aqueous cytosol within cells.
What are sterols
(Steroid alcohols) Type of lipid found in cells.
Not fats or oils and have little in common with them in terms of structure.
Complex alcohol molecules based on a 4 carbon ring structure with a hydroxyl group at one end.
Have duel hydrophobic and hydrophilic characteristics.
Hydroxyl group is polar so hydrophilic and rest of molecule is hydrophobic.
Cholesterol is a sterol; body manufactures it primarily in the liver and intestines; important role in formation of cell membranes.
Adds to stability of cell membranes and regulates their fluidity by keeping membranes fluid at low temps.
Vit. D, steroid hormones and bile are all made using cholesterol.
What’s the role of lipids
Due to non-polar nature:
- membrane formation and creation of hydrophobic barriers.
- hormone production
- electrical insulation necessary for impulse transmission.
- waterproofing like in birds feathers and on plant leaves.
Lipids, triglycerides in particular, have important long-term energy store roles.
Provide: stored under skin and around vital organs
1. thermal insulation to reduce heat loss (e.g. in penguins)
2. cushioning to protect vital organs such as the heart and kidneys.
3. buoyancy for aquatic animals like whales
How can you identify lipids
Can be identified in the laboratory by a simple test = EMULSION TEST
- test is mixed with ethanol
- resulting solution is mixed with water and shaken
- if white emulsion forms as a layer on top it’s a pos. test. If remains clear, it’s neg.
