Biochemical Tests

Question 1

Name of test for proteins

Answer 1

Biuret Test

Question 2

Name of test for reducing and non-reducing sugars

Answer 2

Benedict’s Test

Question 3

Name of test for starch

Answer 3

Iodine test

Question 4

Name of test for lipids

Answer 4

Emulsion test

Question 5

How to carry out Benedict’s Test for reducing sugars

Answer 5

Place sample in boiling tube, add equal volume of Benedict’s Reagent, heat mixture in water bath for five minutes

Question 6

Positive test for reducing or non-reducing sugars

Answer 6

Brick red precipitate

Question 7

Negative test for reducing or non-reducing sugars

Answer 7

Blue precipitate

Question 8

Why is the Benedict test qualitative?

Answer 8

The colour of the precipitate depends on the concentration of reducing sugar

Question 9

How to carry out Benedict’s test for non-reducing sugars

Answer 9

Boil the solution with hydrochloric acid in a water bath, neutralise it with calcium carbonate, add Benedict’s reagent and carry out Benedict’s test as normal

Question 10

Test for starch

Answer 10

Iodine test

Question 11

How to carry out iodine test

Answer 11

Add iodide solution into sample

Question 12

Positive result for starch

Answer 12

Blue-black

Question 13

Negative result for starch

Answer 13

Yellow

Question 14

Alternative test for reducing sugars

Answer 14

Reagent strips

Question 15

Test for lipids

Answer 15

Emulsion test

Question 16

How to do the emulsion test

Answer 16

Mix sample with ethanol, mix resulting solution with water and shake

Question 17

Positive test for lipids

Answer 17

White

Question 18

Negative test for lipids

Answer 18

Clear

Question 19

Test for proteins

Answer 19

Biuret Test

Question 20

How to do the Biuret Test

Answer 20

Add Biuret Reagent, leave in water bath

Question 21

Positive test for proteins

Answer 21

Lilac

Question 22

Negative test for proteins

Answer 22

Blue

Question 23

Quantitative methods of determining the concentration of a substance

Answer 23

Colorimetry, biosensors

Question 24

How to do colorimetry

Answer 24

Filter in colorimeter, calibration of colorimeter with distilled water, Benedict’s test with known concentrations of a solution, filtering of the solutions to remove precipitate, percentage transmission of each solution measured in colorimeter, calibration curve plotted, percentage transmission by sample can then be used to read off the concentration from the curve

Question 25

How do biosensors work?

Answer 25

Molecular recognition when a protein or single strand of DNA that has been immobilised interacts with the molecule being looked for, transducer detects this, produces a response such as releasing a dye or an electric current, display of a particular colour or a particular reading

Question 26

How to do paper chromatography

Answer 26

Wear gloves and draw a line on the chromatography paper relatively close to the bottom edge with 4 equally spaced marks drawn on the line, spot the amino acid solutions onto the marks using a capillary tube, dry the spot, repeat for many spots, place the paper into a jar containing a solvent, close the jar, remove the paper, draw a line along the solvent front, dry, spray with ninhydrin spray which will cause amino acids to turn brown, mark each dot with a pencil

Question 27

Equation for Rf

Answer 27

Rf = Distance travelled by component / Distance travelled by solvent

Question 28

Difference between paper and thin layer chromatography

Answer 28

You use plates rather than paper

Question 29

How can chromatography be used to separate biological molecules?

Answer 29

Different molecules will have different Rf values.

Question 30

Why is it essential that enzymes are the right shape?

Answer 30

Shape is linked to the specificity, substrate wouldn't fit, antibody wouldn't fit the antigen, allows reversible binding

Question 31

Why is it important that proteins fold right?

Answer 31

Won't fit into active sites of enzymes, insoluble, too compact

Question 32

Why can you tell that protein synthesis doesn't use diffusion?

Answer 32

Rate too slow over large distances, large molecules