3.1.3 Lipids Flashcards
Name two groups of lipid?
Triglycerides
Phospholipids
How are triglycerides formed?
The condensation of one molecule of glycerol and three molecules of fatty acid
What bond is formed during the condensation of one molecule of glycerol and three molecules of fatty acid?
Ester bond
Where is the R group in a triglyceride?
The fatty acid molecule
Is the R group of a fatty acid saturated or unsaturated?
It can be both
How does a phospholipid differ from a triglyceride?
One group of fatty acids is removed
A phosphate containing group joins the molecule
How do lipids insulate?
A layer of fat under the skin
How do leaves reduce transpiration?
With a waxy cuticle on the upper surface of the leaf
Why do seeds need a fat store?
As an energy store to aid growth
When oxidised, lipids provide more than twice the energy as carbs and release valuable water
Where else are fats found in animals?
Around organs for protection (eg kidney)
Under the skin for insulation as fats are slow conductors of heat
Where are fats found in cells?
Cell membrane
Separate substances inside and outside cell
Contribute to flexibility
How do insects prevent dehydration?
They have a lipid based waxy cuticle
Why is triglyceride not a polymer?
There are no repeated subunits
What elements are involved in a triglyceride?
Carbon
Hydrogen
Oxygen (least)
What are the properties of a triglyceride?
Insoluble in water
Soluble in organic solvents (alcohol)
What’s the general formula of a triglyceride?
RCOOH
Describe saturated fats?
Single carbon-carbon bonds
Straight chains
More dense at room temperature
Straight chains are compact
Describe unsaturated fats?
One or more carbon-carbon double bonds
Kinky chains as double bonds make it bend
Less dense so liquid at room temperature
Kinky chains can’t be tightly packed
What’s the difference between a monounsaturated fats and polyunsaturated fats?
Monounsaturated fats have just one carbon carbon double bond whereas polyunsaturated fats have more than one carbon carbon double bond
What’s the structure of a triglyceride?
H O
H-C-O-C-R
H O
H-C-O-C-R
H O
H-C-O-C-R
HDescribe the test for a lipid?
Take a dry, grease-free test tube
Add ethanol to solution
Shake to dissolve any lipid
Add water and shake
A cloudy white emulsion indicates a lipid is present
Repeat with water instead of solution X (should remain clear)
Why does a sample containing a lipid produce a cloudy-white colour in the lipids test?
The alcohol with the lipid in doesn’t dissolve in water so forms an emulsion
Why are phospholipids useful as cell membranes?
The two layers of phospholipids have hydrophobic ends facing toward each other to make a micelle which controls what substances come in and out
List the 4 main roles of lipids.
Source of energy
Waterproofing
Insulation
Protection
What is the formula for glycerol?
CH2OH
What is the formula for a fatty acid?
HOOC
Why are hydrocarbon chains with no carbon to carbon double bonds described as saturated?
All carbon atoms are linked to the maximum possible number of hydrogen agoms
What makes triglycerides good storage molecules?
Low mass to energy ratio
Lots of energy stored in a small volume
Good for animals as it reduces the mass they have to carry as they move
Why don’t triglycerides affect the water potential of a cell?
They’re large and non polar
This makes them insoluble in water
So their storage doesn’t affect osmosis in cells
How do triglycerides provide a good source of water?
High ratio of hydrogen to oxygen atoms
This means they release water when oxidised
What makes phospholipids polar?
Each end (pole) behaves differently in water Hydrophilic heads (phosphate molecules) attract water Hydrophobic tails (2 fatty acids) repel water
How does the phospholipid structure have any association with cell recognition?
By combining with carbohydrates within the cell-surface membrane they can form glycolipids
Glycolipids are important in cell recognition
