Lipids Flashcards
What elements are lipids made of?
Carbon, hydrogen and a little oxygen
Why are lipids hydrophobic?
Because they have little oxygen, meaning they have less polar bonds, therefore making them hydrophobic
Do lipids have more or less hydrogen in them than carbohydrates?
More
Are lipids soluble or insoluble in water?
Insoluble
What are lipids soluble in?
- Ethanol
- Organic solvents
What are the two types of lipid?
- Fats -> solid at RT (animals produce mostly fats)
- Oils -> liquid at RT (plants produce mostly oils)
What are 7 functions of lipids?
- Dense energy source
- Insulation
- Protection
- Waterproofing
- Metabolic water
- Buoyancy
- Cell membranes
Why are lipids good for storage?
- Insoluble -> they do not disperse
- They don’t affect water potential
- Energy rich (produce 2x as much energy as carbohydrates)
How are lipids used for insulation?
- Fats are slow conductors of heat so are stored underneath the skin of endothermic to maintain a constant body temperature
- Very important for acquatic organisms
- Also provides electrical insulation around nerves
How are lipids used for protection?
Fat is stored around delicate organs like the kidneys
How are lipids used for waterproofing?
- Water conservation is important to all terrestrial organisms
- Plants and insects have a
waxy cuticle - Mammals secrete an oily substance from sebaceous glands. They repel water so prevent water loss.
How are lipids used as a water source?
Breakdown of triglycerides can provide metabolic water which desert
animals can use
How are lipids used for buoyancy?
Lipids are less dense than water so insulated aquatic animals are buoyant (float) -> aids breathing
How are lipids used in cell membranes?
Phospholipids are a component of cell surface membranes. They add flexibility and act as a barrier in the cell.
What are the types of lipid?
- Simple -> triglycerides (fats, oils), waxes, steroids (hormones that derive from cholesterol)
- Complex -> phospholipids (similar to triglycerides and a component of cell surface membranes), glycolipids
What are triglycerides?
- Made of 3 fatty acids and a glycerol molecule
- Fatty acids contain a carboxyl group (COOH), hence acid
- Uncharged molecule, so insoluble jn water and hydrophobic
How are triglycerides formed?
- In a condensation reaction, the COOH group of the fatty acids react with the OH group of the glycerol molecule, which forms an ester bond
- Water is also formed
- Covalent linkage, so very strong
What is the formula of glycerol?
C₃H₅(OH)₃
What do the properties of triglycerides depend on?
- The fatty acids
- Because glycerol only has one form
What is the difference between saturated and unsaturated fats?
- Saturated -> they don’t have a C=C double bond
- Unsaturated -> that have one or more C=C double bonds
What do mono and polyunsaturated fats mean?
- monounsaturated -> one C=C double bond
- polyunsaturated -> multiple C=C double bonds
What do the C=C double bonds do to the fatty acids?
- Makes the fatty acids bend
- So they can’t pack as closely and the triglyceride is more liquid (oil)
- Double bonds reduce the melting point
What are waxes?
- Lipid molecules where the hydrocarbon chain is linked to an alcohol and not glycerol
- (not digested by animals)
What is the main use of waxes?
- Waterproof covering in living organisms -> e.g outer cuticle on leaves
Why are steroids a type of lipid?
- So that they can pass directly through phospholipid bilateral (including nuclear envelope)
- So can bind to target receptor in nucleus and can act directly on DNA
What is the structure of cholesterol and what does this structure allow them to do?
- Made of 4 carbon rings joined together
- Small narrow structure allow them to sit between phospholipids in membranes
Where is most cholesterol made?
Most is made in the liver (also comes from diet)
What two steroid hormones are made from cholesterol?
- Oestrogen
- Testosterone
What vitamin is made from cholesterol?
Vitamin D (important in calcium absorption, deficiency= rickets)
What does cholesterol do in plasma membranes?
- Regulates membrane fluidity
How do you test for lipids?
- Add ethanol and shake well
- Cloudy white -> positive result
Why does the ethanol test work?
- Lipids are insoluble in water and soluble in ethanol (an alcohol)
- After lipids have been dissolved in ethanol and then added toH2O,they will form tiny dispersed droplets in the water (emulsion)
- Droplets scatter light as it passes through the water so it appears white and cloudy
Give three differences between saturated and unsaturated fats?
- Unsaturated fats have at least one C=C double bond whereas saturated fats have on single bonds.
- Unsaturated fats have a lower melting point than saturated
- Unsaturated -> usually from plants whereas saturated -> usually from animals
