Topic 1A- Biological Molecules (Lipids And Calculations) Flashcards
Describe the basic structure of triglycerides
They have one molecule of glycerol with 3 fatty acids attached to it
Are lipids soluble or insoluble? Why?
Lipids are insoluble. This is because they contain fatty acid molecules which have long ‘tails’ made of hydrocarbons. These tails are hydrophobic (they repel water molecules).
Give 1 way different fatty acids vary
The hydrocarbon tail varies
Describe the basic structure of a fatty acid and draw it
- Central carbon atom
-ester group (=O and -OH)
Variable R group (hydrocarbon tail)
What reaction joins fatty acids to the glycerol molecule
Condensation reactions
Draw the structure of a glycerol molecule
What bond is formed when a fatty acid joins to a glycerol molecule
Ester bond
Explain how the ester bond is formed when glycerol and fatty acid join together
Draw an image also to illustrate this occuring to create a triglyceride
The H from an OH group on the glycerol molecule reacts via a condensation reaction with the OH group from the fatty acid to form H2O. This was leaves an oxygen molecule, so forms an ester bond between the Carbon from the glycerol and the carbon on the fatty acid.
What is the difference between a saturated and unsaturated fatty acid
Unsaturated fatty acids have at least one Carbon - Carbon double bond in the hydrocarbon chain, which causes the chain to kink
However, saturated fatty acids only have single carbon-carbon bonds in the hydrocarbon chain (they are saturated with hydrogen), so form a straight chain
Give the two types of lipid
Triglycerides
Phospholipids
What is the difference between the structure of triglycerides and the structure of phospholipids
In triglycerides, there are 3 fatty acids but in phospholipids, one of the fatty acids is replaced with a phosphate group.
Which type of lipid is found in cell membranes
Phospholipids
Which part of the phospholipid is hydrophilic and which part is hydrophobic
The phosphate group is hydrophilic (attracts water) and the fatty acid tails are hydrophobic (repel water).
What are triglycerides mainly used for
They are mainly used as energy storage molecules
Why are triglycerides good for energy storage (2)
1) the long Hydrocarbon tails of the fatty acids contain lots of energy - a load of energy is released when they’re broken down. Because of this, lipids contain about twice as much energy per gram as carbohydrates.
2) they’re insoluble, so they don’t effect the water potential of the cell they’re stored in (which would cause water to enter the cells by osmosis which would make them swell).
Explain how triglycerides clump together as insoluble droplets in cells
The hydrophobic fatty acid chains face inwards, shielding themselves from water with their hydrophilic glycerol heads
What makes up the bilayer in cell membranes? Explain how they help to complete the function of the cell membrane.
Phospholipids. The function of the cell membrane is to control what enters and leaves the cell.
They do this because their heads are hydrophilic and their tails are hydrophobic, so they can form a double layer with their heads facing out towards the water on each side.
Because the centre of the bilayer is hydrophobic, water-soluble substances can’t easily pass through it therefore the membrane acts as a barrier to them.
What do cell membranes do
Control what enters and leaves the cell
What is the test for lipids called and what do you need to do for it
The emulsion test
1) shake the test substance with Ethanol in a test tube for about a minute to that it dissolves
2) pour distilled water into the solution and shake again
3) Any lipid will show up as a milky emulsion. The more lipid there is, the more noticeable the milky colour will be
