1. AICE Biology Lab Review: Biological Molecules & Enzymes
Prepared by Ms. Evans at GHS
Lab Review ppt: Biological Molecules & Enzymes

2. B. Biological Molecules
(a) carry out tests for reducing and non-reducing sugars (including semi-quantitative use of the Benedict’s test), the iodine in potassium iodide solution test for starch, the emulsion test for lipids and the biuret test for proteins;
Lab Review ppt: Biological Molecules & Enzymes

3. Benedict’s Test: Reducing & Non Reducing Sugars, Round 1
Testing for simple sugars: Benedict's Reagent, round 1
Procedure:
Add Benedicts reagent to sample, place in waterbath until just boiling.
Left to right:
Benedict's reagent (BnR),
potato extract + BnR,
onion extract + BnR,
5% glucose + BnR.
RESULTS:
Aqua-blue = negative.
Green to Yellow to orange = positive.
Note: to detect the simple sugar sucrose, you must do round 2 test
Lab Review ppt: Biological Molecules & Enzymes

4. Benedict’s Test: Reducing & Non Reducing Sugars, Round 2
A Negative result in round one DOES NOT mean an absence of carbohydrates!!
Sucrose is a non-reducing Sugar & can only be detected by doing round 2 of Benedict’s testing (Acid Hydrolysis)
Procedure:
Perform round 1 of Benedict’s Testing. Negative result indicates either no carbohydrate OR Non-reducing Sugars (Sucrose or starch).
How would you test for the presence of starch???
Perform Round 2 of Benedict’s Testing to see if you have sucrose if Starch test is Negative.
Lab Review ppt: Biological Molecules & Enzymes

5. Sample Procedure for Benedict’s Test for Non Reducing Sugar
In a test tube place 5 cm3 solution, add 3 cm3 Benedict's reagent to the solution in the test tube and place the tube in the boiling water bath for five minutes.
Add 1 cm3 dilute hydrochloric acid to the solution solution in your test tube. Note the time and place in the water bath
After 10+ minutes, remove the tube from the water bath & cool it under the tap. Neutralize the acid by adding solid sodium bicarbonate, a little at a time, until the addition of one portion produces no fizzing.
With a dropping pipette place 3 cm3 Benedict's solution in test tube & return to the water bath and heat for five minutes.
A color change indicates that there was Non reducing sugar present. How would you verify that your solution was sucrose & not starch???
Lab Review ppt: Biological Molecules & Enzymes

6. Benedict’s Testing: Sample Question 1
Solutions of four food substances are tested for sugars. The table shows the colours of the solutions after testing.
Which food is a non-reducing sugar?
Lab Review ppt: Biological Molecules & Enzymes

7. Benedict’s Testing: Sample Question 2
Four sugar solutions were tested with a standard Benedicts solution. The table shows the colour of the solutions after testing.
What is the best interpretation of the results?
Lab Review ppt: Biological Molecules & Enzymes

8. Testing for Starch IKI (Iodine in Potassium Iodide)
Left to right:
IKI only,
starch solution,
starch solution + IKI.
RESULTS: Yellow-orange = negative.
Purple-black = positive.
Lab Review ppt: Biological Molecules & Enzymes

9. Emulsion Testing for Lipids
Sample Procedure:
Add 2cm3 fat or oil to a test tube containing 2cm3 of absolute ethanol. Dissolve the lipid by shaking vigorously. Add an equal amount of cold water.
Observation: A cloudy white suspension.
Basis of test:
Lipids are immiscible with water. Adding water to a solution of the lipid in alcohol results in emulsion of tiny droplets in the water which reflect light and give a white , opalescent appearance.
Lab Review ppt: Biological Molecules & Enzymes

10. Testing for Polypeptides (proteins) Biuret’s Reagent
Left to right:
Biuret's reagent (BrR),
water + BrR,
egg albumin solution,
egg albumin solution+ BrR.
RESULTS:
Denim-blue = negative.
Lavender = positive.
Lab Review ppt: Biological Molecules & Enzymes

11. Acid hydrolysis then Benedict’s
Identify each sample
Food tests are carried out on four unknown chemicals. The chart below shows the results of each test.
Solution
Benedict’s Test
Acid hydrolysis then Benedict’s
IKI
Biuret
Emulsion A X + B C D
(KEY: + = positive result , X = negative result)
Lab Review ppt: Biological Molecules & Enzymes

12. C. Enzymes
(c) follow the time course of an enzyme-catalysed reaction by measuring rates of formation of products (for example, using catalase) or rates of disappearance of substrate (for example, using amylase)
Lab Review ppt: Biological Molecules & Enzymes

13. Enzymes
(d) investigate and explain the effects of temperature, pH, enzyme concentration and substrate concentration on the rate of enzyme-catalysed reactions, and explain these effects;
Practice Question 1:
The curve X shows the activity of an enzyme at 20oC. Curves A to D show the effect of different conditions on the activity of the enzyme.
Which curve shows the effect of increasing the temperature by 10o C and adding extra substrate?
Lab Review ppt: Biological Molecules & Enzymes

14. Enzymes Practice Question 2
The graphs show the effects of temperature and pH on enzyme activity.
Which statement explains the enzyme activity at the point shown?
A. At P, hydrogen bonds are formed between enzyme & substrate.
B. At Q, the kinetic energy of enzyme and substrate is highest.
C. At R, peptide bonds in the enzyme begin to break.
D. At S, the substrate is completely denatured.
Lab Review ppt: Biological Molecules & Enzymes

15. Enzymes Practice Question 3
The graph shows the effect of substrate concentration on the rate of an enzyme-controlled reaction. The enzyme concentration is constant.
Which statement about the graph is correct?
Between W and X, the number of enzyme molecules is limiting.
B. Between X and Y, the number of enzyme molecules is limiting.
C. Between X and Y, the number of substrate molecules is limiting.
D. Between X and Y, the product concentration remains the same.
Lab Review ppt: Biological Molecules & Enzymes