lipids Flashcards
(20 cards)
what elements do lipids contain?
lipids contain the elements, carbon, hydrogen and oxygen
how does the proportions of oxygen and hydrogen differ in lipids than in carbohydrates?
lipids possess a lower proportion of oxygen and a higher proportion of hydrogen compared to carbohydrates
what are lipids used in an for?
they are used in respiration and as structural and storage molecules
what are the two types of lipids?
triglycerides and phospholipids
what are triglycerides?
triglycerides are ideal storage compounds yielding twice as much energy as carbohydrates when fully oxidised (respired), and being insoluble, are osmotically inactive
what do triglycerides consist of?
triglycerides consist of fats (solids) and oils (liquids) at room temperature
what are triglycerides soluble and insoluble in?
although insoluble in water, triglycerides are soluble in a range of organic solvents e.g. alcohol
how are triglycerides formed?
triglycerides are one type of lipid formed by joining 3 fatty acids to one glycerol molecule during a condensation reaction with the loss of three water molecules
what is the general formula of a fatty acid?
the general formula of a fatty acid is R-COOH
what does R and COOH represent?
the R represents a long hydrocarbon chain and COOH is a carboxylic acid group
what two things can the fatty acids be?
the fatty acids can be saturated and unsaturated
define saturated and unsaturated
saturated - no double bonds between the carbon atoms, contain the maximum number of hydrogen atoms
unsaturated - contain one or more double bonds between the carbon atoms, do not contain the maximum number of hydrogen atoms
what are simple and mixed triglycerides?
simple triglyceride - three fatty acids all the same
mixed triglyceride - three fatty acids are different
how are lipids hydrolysed?
lipids can be hydrolysed into fatty acids and glycerol by
- heating with acid or alkali.
- using the enzyme lipase at an optimum temperature and pH
describe how to carry out a test for lipids
lipids can be detected in a sample by using the emulsion test:
- a small amount of the sample is placed into a test tube with 2cm^3 of ethanol
- shake the mixture so that the fat dissolves
- add this to water in another test tube and mix the contents
- a white or cloudy emulsion of fat droplets indicates lipid is present
what are phospholipids?
phospholipids are lipids containing a phosphate group
what does a phospholipid molecule consist of?
a phospholipid molecule consists of one glycerol, two fatty acids and a phosphate group (which replaces one of the fatty acid molecules) joined in a condensation reaction
what is the structure of a phospholipid molecule?
the phospholipid molecule has a polar hydrophilic head (attracts water) containing the phosphate group, and a non polar hydrophobic tail (repels water) consisting of the long fatty acids chains
what does a thin layer of phospholipids in contact with water form?
a thin layer of phospholipids in contact with water forms a single layer as the hydrophilic heads are attracted to the water whereas the hydrophobic tails are water repellent and project outwards
how are phospholipids arranged in the cell membrane?
in the cell membrane a bilayer of phospholipids is present as the non polar hydrophobic tails are attracted to each other and away from water and the polar hydrophilic heads are oriented outwards
