Biological Molecules Flashcards
Draw two molecules of alpha glucose and circle where they form a glycosidic bond.
OH below the plane
Circle should be around OH group on carbon 1 and 4 from glucose monomers
Describe how you would test for a non-reducing sugar.
First add Benedict’s solution and heat to 90C to test for any reducing sugars.
If solution does not change colours non present
Boil with Hydrochloric acid and then sodium hydrogen carbonate to neutralise.
Add Benedict’s and heat to 90C
Should turn dark red in presence of non-reducing sugars
How do you test for presence of a lipid?
Add a drop of water, then a drop of ethanol + shake
If a white emulsion is formed it contains lipids.
Describe a method to find the concentration of glucose in an unknown solution.
Plot a calibration curve
Prepare known solutions of glucose and add Benedict’s solution to them and place them in a water bath at 90C for 5 minutes.
Filter the precipitate and then add it to a cuvette.
Place into a colorimeter and measure absorbance of green light
Plot these points onto a graph.
Repeat Benedict’s test with unknown solution and then place precipitate into cuvette and measure absorbance of green light.
Read off calibration curve to see concentration of glucose.
Suggest a method other than colorimetry to measure the quantity of reducing sugar in a solution.
Add Benedict’s solution and place in water bath at 90C for 5 minutes.
Remove from water bath and filter to remove the precipitate from the solution.
Dry precipitate using heat gun and then measure dry mass as this is proportional to mass of glucose in solution.
Describe and explain the features of starch that make it a good storage molecule
Insoluble so doesn’t effect water potential of cell
Coiled into alpha helix so is compact
Branched so more ends for faster enzyme breakdown
Large molecule so cannot cross cell membrane
Polymer of alpha glucose so provides respiratory substrate
Describe and explain two features of cellulose that mean it is adapted to its function.
Long straight chains form hydrogen bonds between them to form fibrils which provide strength as structural molecule
Insoluble so does not effect water potential
Describe two differences between the structure of a glycogen and cellulose molecule.
Glycogen is Alpha Glucose cellulose is Beta
Cellulose is a straight chain and glycogen is branched
Glycogen is coiled and cellulose is straight
Glycogen has 1-4 and 1-6 but cellulose only has 1-4 glycosidic bonds
Describe how you would test for the presence of a lipid.
Add a drop of water
Add ethanol
Shake and a white emulsion is formed
Describe how a triglyceride molecule is formed.
Glycerol and three fatty acids
Condensation reaction between each one and removal of three water molecules
Forms an ester bond
Describe the induced fit model of an enzyme.
Substrate binds to enzyme active site
Tertiary structure is altered and active site changes slightly and becomes complementary to substrate
Describe how enzymes act as catalysts.
Lowers activation energy
Induced fit causes active site to change shapes
So enzyme substrate complex causes bonds to form or break
Describe a biochemical test to test for the presence of proteins in a solution.
Add biuret solution + shake
goes from blue to violet/purple
Describe two ways in which all dipeptides are the same and one way in which they are different.
Similarities- peptide bond
NH2 at one end
COOH at one end
Two R groups
Differences- different R groups
Describe how a non-competitive inhibitor reduces the rate of an enzyme controlled reaction.
Binds to allosteric site of the enzyme
Causes a change in tertiary structure which causes the shape of the active site to change
No longer complementary to substrate so no enzyme-substrate complexes formed
