3.5 Lipids Flashcards
What elements do lipids contain?
Carbon, Hydrogen and Oxygen
What are lipids commonly known as?
Fats and oils.
Are lipids polar or non-polar?
Non-polar, the electrons in outer orbitals are evenly distributed
What are lipids built from?
Repeating monomers
Are lipids macro or micromolecules?
Macromolecules; they are large complex molecules
What is the structure of a triglyceride?
One glycerol molecule combined with 3 fatty acids (fatty acids are either all identical or all different)
What functional group do fatty acids belong to?
Carboxyl group (-COOH)
Describe the structure of a fatty acid.
A hydrocarbon attached to the carboxyl functional group.
Describe the general formula for a fatty acid.
RCOOH (Where R is the variable number of carbon and hydrogen atoms)
What do both glycerol and fatty acids contain?
Hydroxyl groups (OH)
How does a triglyceride form?
The hydroxyl groups of the fatty acids and the glycerol interact in a condensation reaction, formation 3 water molecules and an ester bond between the fatty acids and glycerol molecule.
What is the formula for an ester bond?
RCOOR
What kind of reaction is required to break down a triglyceride?
A hydrolysis reaction. The three water molecules produced in the condensation reaction need to be supplied back.
What makes a fatty acid saturated, and why?
If they have no double bonds between the carbon atoms, because all the carbon atoms have formed the maximum number of bonds with hydrogen atoms (they are saturated with hydrogen bonds)
What is the name for if there is one double bond in a fatty acid?
Monounsaturated
What is the name for if there are two or more double bonds in a fatty acid?
Polyunsaturated
Why are unsaturated fatty acids liquids at room temperature?
Because the presence of double bonds causes the molecule to bend, so they cannot pack so closely together.
What is the general formula for a saturated fatty acid?
CnH2n+1 COOH
Why are lipids long-term energy stores?
Because when fats/oils are hydrolysed, a large amount of energy is released (because the bonds between carbon and hydrogen in the fatty acids contain large amounts of energy).
Describe the structure of a phospholipid.
2 fatty acids are bonded to a glycerol molecule. This glycerol molecule is attached to a phosphate group
What is a phosphate group?
The same as a phosphate ion. PO4 (3-)
What are the two key sections of a phospholipid?
Hydrophobic tails (two fatty acids), hydrophilic head (the glycerol and phosphate group)
Is phosphate polar or non-polar?
Polar (all ions are polar)
Is the hydrophilic head of a phospholipid charged?
Yes, negatively charged
Are the hydrophobic tails of a phospholipid charged?
No
Describe what happens to a phospholipid when in water.
-The hydrophilic head will interact and dissolve in the water
-Hydrophobic fatty acid tails will stick out of the water
-Phospholipids form a monolayer on the surface of the water
-Phospholipids are insoluble in water
What is the name of the structure that phospholipids form when in an aqueous environment?
Two-layered sheet formation (bilayer)
Describe the bilayer that phospholipids form when in an aqueous solution.
Hydrophobic tails point towards the centre of the sheet, protected from the water by hydrophilic heads
Why do phospholipids play a key role in forming cell membranes?
Because of the bilayer arrangement that they form, and because they can therefore separate an aqueous environment from the aqueous cytosol within cells.
What chemical do you use to test for lipids?
Ethanol
Describe the method for testing for lipids.
1) If testing solid food, grind up the food using a pestle or mortar
2) Add a solvent, like ethanol, to the food sample
3) Place a bung in the test tube and shake thoroughly so that any lipid will dissolve in the solvent
4) Decant the lipid/solvent mixture into a test tube of distilled water
5) The presence of a white emulsion (cloudy) indicates the presence of a starch
6) The degree of cloudiness indicates the amount of lipid present
What is a sterol?
A type of alcohol
Describe the two ends on a sterol.
One hydroxyl, polar, hydrophilic end and one non-polar, hydrophobic end
What is an important use of cholesterol?
Used in the structure of cell membranes, to add stability and regulate their fluidity, by keeping the membrane fluid at a low temperature.
Describe the relationship between cholesterol and phospholipids in the cell membrane
The hydrophilic ened of the cholesterol molecule is attracted to the hydrophilic heads of the phospholipid.
Where does the body manufacture cholesterol?
In the liver and intestines
What are the biological roles of lipids that they have due to their non-polar nature?
-Membrane formation (formation of hydrophobic barriers)
-Hormone production
-Electrical insulation necessary for impulse transmission
-Waterproofing (eg in bird’s feathers)
-Buoyancy for aquatic animals
-Cushioning to protect vital organs
-Thermal insulation to reduce heat loss.
