Lesson 8 - Lipids Flashcards
Lipids:
Fats and oils
What elements do lipids contain?
Hydrogen , oxygen, carbon
State at room temperature: fats
Solid
State at room temperature: oils
liquid
Why are lipids non-polar molecules
Electrons in the outer orbitals that form bonds are more evenly distributed than in polar molecules. No positive or negative regions.
What is the result of lipids being non-polar?
Not soluble in water
Other word for large complex molecules:
Macromolecules
How are triglycerides made?
By combining one glycerol molecule with three fatty acids
Glycerol group
Alcohols
Fatty acids group
Carboxylic acids. (-COOH) with a hydrocarbon chain attached.
Carboxylic group
-COOH
Bonding in triglycerides:
Hydroxyl (OH) groups interact in both glycerol and fatty acids. This leads to the formation of three water molecules and bonds between the glycerol and fatty acids.
These are ester bonds.
What is the name of the type of reaction that forms triglycerides?
Esterification.
What is esterification an example of?
Condensation reaction
Hydrolysis of triglycerides?
Three water molecules supplied.
Saturated fatty acids:
Fatty acid chains that have no double bonds present between the carbon atoms are called saturated. This is because all the carbon atoms form the maximum number of bonds with hydrogen atoms.
Unsaturated fatty acids:
A fatty acid with double bonds between some carbon atoms
One double bond between fatty acids:
Monounsaturated
Two or more double bonds present in fatty acids:
Polyunsaturated
Effect of double bonds in fatty acids:
Molecules kink or bend so they can not pack closely. This makes them a liquid at room temperature rather than a solid. So they are oils.
Plants contain triglyceride oils:
They tend to be more healthy in the human diet than saturated triglycerides or (solid) fats. There is evidence that excess unsaturated fats can lead to CHD, but evidence is inconclusive.
All types of fat can lead to obesity and put strain on the heart.
Saturated?
No double bonds between carbon atoms
Monosaturated?
One double bond between carbon atoms
Polysaturated?
2 or more double bonds between carbon atoms.
What is the result of a double bond between carbon?
Cause the molecule to bend. They can noy pack together so closely so form a liquid at room temperature.
What are phospholipids?
Modified triglycerides and contain the elements phosphorus, carbon, hydrogen, and oxygen.
Where are inorganic phosphate ions found?
Cytoplasm of every cell.
Formula of phosphate?
PO4^3+
Why are phosphate soluble in water?
Have extra electrons as ions so are negatively charged.
How are triglycerides modified to form phospholipids?
One fatty acid chain is replaced by a phosphate group.
Structure of phospholipids?
- Charged hydrophilic head
- Non-polar hydrophobic tails (fatty acids)
Point of the non-polar hydrophobic tails?
Repelled by water but mix readily with fat
Point of the charged head?
Interact with and attracted to water
How do phospholipids interact with water?
Form a layer on the surface of water. Phosphate heads in the water and fatty acid tails sticking out.
Other name for phospholipids?
Surface active agents / surfactants
How they form phospholipid bilayer?
Tow layered sheet with the hydrophobic tails pointing towards the centre of the sheet, protected from water by the hydrophilic heads.
Why are phospholipid bilayers used to form cell membranes?
Separate aqueous environment in which cells exist from aqueous cytosol in cells.
How is it believed that the first cells were formed?
As phospholipid bilayers. They then became cell membranes.
Steroid Alcohols
Steroids
Where are steroids found?
Cells
Structure of steroids?
- 4 carbon ring structure
- hydroxyl (OH) group at one end
- complex alcohol molecules
How do steroids have dual hydrophobic and hydrophilic properties?
OH group is hydrophilic
Rest of molecule is hydrophobic
Example of a sterol?
Cholesterol
Where is cholesterol manufactured in the body?
Liver and intestines
Role of cholesterol?
Formation of cell membranes –> positioned between the phospholipids. OH hydroxyl group at the periphery of the membrane.
Why is cholesterol in the cell membrane?
- Adds to the stability
- Regulates fluidity of cell membranes by:
Keeping membranes fluid at low temperatures.
Stopping them from becoming too fluid at high temperatures.
What is manufactured using cholesterol?
- Vitamin D
- Steroid hormones
- Bile
Roles of lipids due to non-polar nature?
- Membrane formation and the creation of hydrophobic barriers.
- Hormone production
- Electrical insulation necessary for impulse transmission.
- Waterproofing (birds feathers and plants leaves)
Storage via lipids?
- Triglycerides (long term energy storage)
Stored under skin and around vital organs.
Storage of lipids provides:
- Thermal insulation to reduce heat loss
- Cushioning to protect vital organs such as the heart and kidneys.
- Buoyancy for aquatic animals like whales.
Identification of lipids test:
Name
Emulsion
Identification of lipids test:
Steps?
- Add 2cm2 test solution and 5cm2 ethanol to the test tube.
- Shake the test tube thoroughly.
- Add 5cm2 of water and shake again.
- White cloudy emulsion forms.
Why does a white cloudy emulsion form?
Light is refracted as it passes from droplets of oil to droplets of water.
Food synergy:
Nutrients do not work in isolation but as part of the combined effect of a whole range of nutrients.
What can help prevent certain types of heart disease?
A combination of fish, fruit, vegetables.
Why do people respond differently to different nutrients?
Different genetic make-up.
Faults with studies on food nutrition?
- Small number of subjects
- People underestimate what they eat. Can’t remember or don’t know the ingredients.
- Technology develops and so understanding of biological processes increases.
Benefits of triglycerides as a storage molecule
- Long hydrocarbon tails - Their many carbon-hydrogen bonds can be broken to release energy.
- Low mass to energy ratio - Lots of energy can be stored in a small volume.
- Insoluble - They do not affect the water potential of cells as they are large and non-polar.
- High ratio of hydrogen to oxygen atoms - Triglycerides will release water when oxidised.
