Lipids (page 24 - 25) Flashcards
You need to learn about three types of Lipids, name them?
Triglycerides
Phospholipids
Cholesterol
What are Triglycerides?
Triglycerides are a kind of lipid.
they are macromolecules.
What are macromolecules?
they are complex molecules with a relatively large molecular mass. (triglycerides are macromolecules).
What chemical elements do Triglycerides contain?
like all lipids, they contain the chemical elements
carbon, hydrogen and oxygen.
What molecules do Triglycerides have?
they have one molecules of glycerol with three fatty acids attached to it. (see diagram 1 on page 24)
Explain the structure of a Triglyceride fatty acids?
fatty acid molecules have long ‘tails’ made of hydrocarbons (compounds that contain only carbon and hydrogen atoms).
The tails are hydrophobic (they repel water molecules). These tails make lipids insoluble in water. All fatty acids have the same basic structure but the hydrocarbon tail varies. (see diagram 1 on page 24). - Variable ‘R’ group hydrocarbon tail.
What do Tyiglycerides contain?
they contain Ester Bonds
Triglycerides are synthesised by the formation of an ester bond between what?
between each fatty acid and the glycerol molecule. (see diagram 2 on page 24).
Each ester bond is formed by what reaction?
ester bond is formed by a condensation reaction (in which a water molecule is released).
What is the process called in which triglycerides are synthesised?
esterification.
When do Triglycerides break down?
when the ester bonds are broken. Each ester bond is broken in a hydrolysis reaction (in which a water molecule is used up).
There are two kinds of fatty acids, name them? and how do you know the difference?
saturated and unsaturated.
The difference is their hydrocarbon tails.
How many double bonds do saturated fatty acids have between their carbon atoms?
saturated fatty acids dont have any double bonds between their carbon atoms. The fatty acid is ‘saturated’ with hydrogen.
see diagram 3 on page 24 at the saturated hydrocarbon chain.
What is the general formula for a saturated fatty acid?
CnH(2n + 1)COOH
How many double bonds do unsaturated fatty acids have between their carbon atoms, and explain what happens to the chain?
Unsaturated fatty acids have at least ONE double bond between carbon atoms, which causes the chain to kink.
look at diagram 4 on page 24 of the unsaturated hydrobarbon chain.
What are Phospholipids?
Phospholipids are also macromolecules. they are similar to triglycerides expect one of the fatty acid molecules is replaced by a phosphate group. (see diagram 5 on page 24 of the phospholipid structure)
The Phosphate group is Hydrophillic, what do this mean?
it attracts water molecules and the fatty acid tails are hydrophobic.
You need to know how the properties of triglycerides, phospholipids and cholesterol are related to their functions.
In animals and plants, triglycerides are mainly used as what?
energy storage molecules.
Some bacteria (e.g. Mycobacterium tuberculosis) use tryglycerides to store both energy and carbon. Why are Triglycerides good for storage?
1) The long hydrocarbon tails of the fatty acids contain lots of chemical energy - a load of energy is released when they’re broken down. Because of these tails, lipids contain about twice as much energy per gram as carbohydrates.
2) They’re insoluble, so they don’t cause water to enter the cells by osmosis (see page 58) which would make them swell. The triglycerides bundle together as insoluble droplets in cells because the fatty acid tails are hydrophobic (water repelling) - the tails face inwards, shielding themselves away from water with their glycerol heads. (see diagram 1 on page 25)
Where are Phospholipids found?
in the cell membranes of all eukaryotes and prokaryotes.
They make up wha’t known as the phosphholipid bilayer.
Regarding Phospholipids, cell membranes control what enters and leaves a cell, explain how?
1) Phospholipid heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side (see diagram 2 on page 25).
2) The centre of the bilayer is hydrophobic, so water-soluble substances can’t easily pass through it - the membrane acts as a barrier to those substances.
Explain the structure of the Cholesterol?
Cholesterol is another type of lipid - it has a hydrocarbon ring structure attached to a hydrocarbon tail. The ring structure has a polar hydroxl (OH) group attached to it.
In eukaryotic cells, cholesterol molecules help strengthen the cell membrane, how?
by interacting with the phospholipid bilayer.
1) Cholesterol has a small size and flattened shape - this allows cholesterol to fit in between the phospholipid molecules in the membrane (see diagram 3 on page 25).
2) They bind to the hydrophobic tails of the phospholipids, causing them to pack more cloesly together. This helps to make the membrane less fulid and more rigid.
What do ‘polar’ mean?
it means it has a slightly negatively charged bit and a slightly positely charged bit. (see page 20).
