Lipids Flashcards
What are the main properties of lipids?
- They contain carbon, hydrogen and oxygen
- The proportion of carbon : oxygen and hydrogen is smaller than in carbohydrates - They are non-polar (triglycerides)
- They are insoluble in water but soluble in organic solvents (e.g. alcohols, acetone)
What are the main functions of lipids?
- Storage of energy for long term use
- Hormonal roles
- Insulation - thermal and electrical
- Protection of internal organs
- Structural components of cells
Remember SHIPS
What are the 2 main types of lipids?
- Triglycerides
- Phospholipids
What is meant by a macromolecule?
Lipids are examples of macromolecules - these are large molecules composed of several smaller ones that are not necessarily polymers.
How do triglycerides form?
They form when condensation reactions occur between 1 glycerol and 3 fatty acids.
The hydroxyl groups of the glycerol combine with the carboxyl groups of the fatty acids to form an ester linkage.
How do ester bonds form?
An ester bond forms when a hydroxyl group (-OH) group from the glycerol bonds with the carboxyl (-COOH) group of the fatty acids.
Why is esterification a condensation reaction?
A hydrogen from the glycerol combines with an OH from the fatty acid, making water.
This happens three times to form a triglyceride, meaning 3 water molecules are formed and released. This makes esterification a condensation reaction.
How are triglycerides stored in animals and plants?
They are stored as fats (solid) in animals and as oils (liquid) in plants.
What are fatty acids?
Fatty acids are long hydrocarbon chains which may differ in length and in the number of double bonds.
What is meant by a saturated fatty acid?
A fatty acid that possesses no double bonds.
This means it has the maximum amount of H atoms.
What are the properties of saturated fatty acids?
- They are usually solid at room temperature
- They originate from animal sources (fats)
- They are linear in structure
What is meant by unsaturated fatty acids?
Fatty acids with double bonds.
They can either be monounsaturated (1 double bond) or polyunsaturated (more than 1 double bond).
What are the properties of unsaturated fatty acids?
- They are bent in structure (known as kinks)
- They are usually liquid (oils) at room temperature
- They originate from plant sources
How is a phospholipid structured?
Phospholipids consist of 1 glycerol, 2 fatty acids and a phosphate group (PO4^3-)
How is the phosphate group bonded to the glycerol in a phospholipid?
They are joined by a phosphoester bond.
What is meant by the “polar head” of a phospholipid?
The glycerol and the phosphate group.
What is the key property of the polar head of a phospholipid?
It is hydrophilic, meaning it attracts water.
What is the key property of the fatty acid tails in a phospholipid?
They are hydrophobic, meaning they repel water.
What is meant by “amphipathic” and why is this significant?
Phospholipids are amphipathic which means they have both hydrophilic and hydrophobic parts.
This allows them to form monolayers or bilayers in water.
How do phospholipids form a bilayer in water?
The fatty acid tails face inwards towards each other, and the polar heads face outwards, dissolving in the aqueous intra and extracellular fluids.
Why is it important that phospholipids can form bilayers in water?
- The hydrophilic heads can be used to hold at the surface of the cell surface membrane
- Their structure allows them to form glycolipids with carbohydrates which are important on the plasma membrane for cell recognition.
- They are ideal for forming plasma membranes as they enable integration of other molecules and help regulate the movement of substances into and out of the cell.
What is the third key type of lipid?
Sterols (steroid alcohols) including cholesterol.
Cholesterol is manufactured primarily in the liver and intestines.
How is cholesterol structured?
It has a 4 carbon ring structure with a hydroxyl group at one end.
It forms a small, thin molecule that fits into the lipid bilayer, providing strength and stability.
What is the function of cholesterol?
It is important in the formation and fluidity of cell surface membranes and in the production of certain hormones (e.g. testosterone).
It is also needed to make vitamin D.
