Lipids Flashcards
What are triglycerides and phospholipids?
Two groups of lipid
How are triglycerides formed?
By the condensation of one molecule of glycerol and three molecules of fatty acid.
How is an ester bond formed?
A condensation reaction between glycerol and a fatty acid (RCOOH)
What are Lipids?
Biological molecules made of carbon, hydrogen and oxygen which are only soluble in organic solvents such as alcohols
What are Triglycerides?
Lipids made of one molecule of glycerol and three fatty acids joined by ester bonds formed in the condensation reactions.
What are fatty acids and describe their appearance
There are many different types of fatty acids (over
70 different types) which vary in chain length, presence and a number of double bonds.
- The R-group of a fatty acid may be saturated or unsaturated.
What is a Saturated Lipid?
Saturated lipids don’t contain any carbon-carbon double bonds - such as those found in animal fats
What is an Unsaturated Lipid?
unsaturated lipids contain carbon-carbon double bonds. - which can be found in plants
What does the presence of double bonds mean in the properties of a molecule?
The presence of a double bond means that the molecule is able to bend. As a result, unsaturated fats cannot pack together as tightly and are therefore liquid at room temperature.
What is a phospholipid?
one of the fatty acids of a triglyceride is substituted by a phosphate-containing group.
Describe the structure and components of a phospholipid
- Phosphate heads are hydrophilic (loves/attracts water) and the tails are hydrophobic (hates/resists water) and as a result phospholipids form micelles when they are in contact with water.
The molecule is therefore known as polar
What test is used to test for the presence of lipids
Emulsion Test
How do you carry out an Emulsion Test?
- Take a completely grease-free test tube and add 2cm3 of the sample to be tested and 5cm3 of ethanol.
- Shake the test tube thoroughly to dissolve all the lipid in the solution.
- Add 5cm3 of water and shake gently.
- A cloudy-white colour indicates the presence of lipid.
- As a control repeat the experiment using water as the sample, the final solution should remain clear.
How is the phospholipid structure related to its properties
- In an aqueous environment being polar means a bilayer can be formed.
- The hydrophilic heads of the phospholipids can be used to hold at the surface of the cell surface membrane.
- Their structure allows them to form glycolipids with carbohydrates which are important on the cell surface membrane for cell recognition.
How is the Triglyceride structure related to its properties
- High ratio of energy-storing carbon-hydrogen bonds to carbon atoms and therefore they are an excellent energy store.
- A low mass to energy ratio meaning that they are a good storage molecule, with a lot of energy being stored in a small volume. This is beneficial for animals as it is less mass to move around.
- Being large and non-polar lipids are insoluble in water and therefore their storage does not affect the water potential of cells.
- A high ratio of hydrogen-oxygen atoms means that triglycerides release water when they are oxidised and therefore provide an important source of water for organisms to live in dry environments.
What are micelles?
The products of lipase digestion remain in association with the bile salts to form structures. (Travel through the ileum)
The word hydrolysis is defined as the lysis of water. How does this apply to polymers?
Polymers break by separating water into hydrogen and hydroxyl groups that are added to the monomers.
What are three functions that lipids serve in plants and/or animals?
Lipids serve in the storage of energy, as a structural component of hormones, and as signalling molecules.
How do phospholipids contribute to cell membrane structure?
Phospholipids orient their heads towards the polar molecules and tails in the interior of the membrane, thus forming a bilayer
What type of compound functions in hormone production, contributes to membrane flexibility, and is the starting molecule for bile salts?
Cholesterol, which is a lipid and also steroid, functions here
Cholesterol is a precursor to hormones, such as testosterone. Testosterone is a male sex hormone that has a key role in sperm production.
How is testosterone most likely to enter target cells?
Directly through the membrane
Amphipathic molecules are both hydrophobic and hydrophilic. Which of the following molecules could be described as amphipathic?
Phospholipids
Relate the structure of triglycerides to their functions.
- High energy: mass ration = high calorific value from oxidation (energy storage)
- Insoluble hydrocarbon chain - won’t affect ψ
Used for waterproofing - Slow conductor of heat = thermal insulation eg adipose tissue
- Less dense than water = buoyancy of aquatic animals
Describe the structure and function of phospholipids.
Amiphiatic molecule:glycerol backbone attached to 2 hydrophobic fatty acid tails & 1 hydrophilic polar phosphate head
- Forms phospholipid bilateral in water = component of membranes
- Tails can splay outwards = waterproofing
Compare phospholipids and triglycerides
- Both have glycerol backbone
- Both may be attached to a mixture of saturated, monounsaturated & polyunsaturated fatty acids.
- Both contain C,H,O
- Both formed by Condensation reactions.
Contrast phospholipids and triglycerides
Phospholipids:
- 2 Fatty acids & 1 phosphate group attached
- Hydrophilic head & hydrophobic tail
- Used in primarily in membrane formation
Triglycerides
• 3 Fatty afire attached
• Entire molecule is hydrophobic
• Used primarily as storage molecule (oxidation releases energy)
What is the most common number of carbon atoms found is fatty acids?
12-18 carbons
emulsion
Small droplets of a substance are suspended in another solution
when testing for a lipid how many minutes do you leave the test upright for
2-3 minutes
