Unit 2 - Testing for biological molecules Flashcards Preview

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Flashcards in Unit 2 - Testing for biological molecules Deck (20)
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1
Q

Explain the iodine test.

A
  • Tests for the presence of starch
  • Add iodine dissolved in potassium iodide solution to test sample
  • If starch is present the colour will change from brown/orange to dark blue/black
  • If no starch is present, the colour stays brown/orange
2
Q

Explain the Biuret test.

A
  • Test for the presence of protein
  • The test solution needs to be alkaline so first step is to add few drops of sodium hydroxide solution
  • Next add the copper (ii) sulphate solution
  • If protein is present (positive result) the solution turns pale purple
  • If no protein is present (negative result) then the solution stays pale blue
3
Q

What is used to test for starch?

A

Iodine

4
Q

Why does iodine turn starch blue?

A

When dissolved in potassium iodide the iodine forms a tri-iodide ion, which slips into the middle of the amylose helix.

5
Q

What does the biuret test really discover?

A

Peptide bonds in proteins

6
Q

How is the colour formed in the biuret test?

A

Colour is formed by a complex between the nitrogen atoms in a peptide chain and Cu2+ ions

7
Q

Explain the Emulsion test.

A
  • Tests for the presence of lipids
  • Shake test sample with ethanol for about 1 minute then pour solution into water
  • If lipid is present, solution turns milky
  • The more lipid present, the more noticeable the milky colour
  • If there is no lipid present the solution stays clear
8
Q

What is used to test for reducing sugars?

A

Benedict’s solution

9
Q

Explain the steps in the Benedict’s test.

A
  • Add Benedicts reagent (blue) to sample
  • Heat it in water bath that’s been brought to boil
  • Watch for colour change
  • Colour of precipitate changes from: blue - green - yellow - orange - brick red
  • If positive result, forms coloured precipitate
  • The higher the concentration of reducing sugar, further the colour change goes (used to compare amount of reducing sugars in different solutions)
10
Q

Define reducing sugar

A
  • A sugar which can give electrons (reduce) to other molecules
  • Reducing sugars include all monosaccharides and some disaccharides
11
Q

What causes the change in colour of the Benedict’s solution?

A

The Cu2+ in benidict solution reduces into Cu+ making copper oxide giving that orange colour

12
Q

What else can test for reducing sugars?

A

Commercially manufactured test strips
Glucose strips like for testing for diabetes etc

13
Q

What are biosensors?

A
  • Biosensors use biological components to determine the presence and concentration of molecules
  • Glucose blood strips are an example
  • Blood is the alayte which is placed onto the test strip,
  • Molecular recognition uses glucose oxidase immobilised upon the surface of the strip
  • Glucose in the blood reacts with a glucose oxidase producing gluconic acid causing a change in the tranducer (a change in the current between the terminals of a glucose monitor)
  • Data is processed by the glucose monitor to give a reading dependent upon the current
14
Q

Why are glucose test strips useful and how do glucose test strips work?

A
  • Useful to test a person’s urine for reducing sugars which could indicate if person has diabete
  • Also can help a diabetic person to manage their bloods
  • Glucose tested using test strips coated in reagent (Benedict’s solution)
  • Strips dipped in test solution and change colour if glucose (reducing sugar) is present
  • Colour change is compared to chart to give indication of the concentration of glucose present

N.B this test only shows presence of a reducing sugar, which could be glucose, this is why a blood test is then done to determine if this is glucose

15
Q

What is a more accurate method than the Benedict’s test to compare the amount of reducing sugars in different solutions?

A

Filter the solution and weigh the precipitate

16
Q

What is the test for non-reducing sugars?

A

Benedict’s test

17
Q

What must first happen to the sugar solution before it can tested for non-reducing sugars?

A

Boiled with hydrochloric acid to hydrolyse the bonds and free up the reducing sugar group e.g. Sucrose split into glucose and fructose

18
Q

After adding hydrochloric acid to free up the reducing sugar group, what must be added to the testing solution to neutralise the acid?

A

Sodium hydrogen carbonate

19
Q

What are the non-reducing sugars Benedict’s test results?

A
  • Positive result, forms coloured precipitate.
  • Colour changes:
    • Blue - Green - Yellow - Orange - Red
  • Negative result, stays blue so no sugar present
20
Q

How can colorimetry be used to calculate the concentraction of reducing sugar present?

A
  • A colorimeter is a piece of equipement that quantitatively measures the absorbance, or transmission, of light be a coloured solution.
  • The more concentrated a solution is the more light it will absorb and the less light it will transmit.