Biochemical Tests

What does qualitative testing determine?

Wether a substance is present in a sample

What does the biuret test test for?

Proteins

What test determines the presence of proteins?

Biuret test

Explain the biuret test for proteins

• Add a few drops of sodium hydroxide solution to a test tube to make it

• alkaline

• Then add copper sulfate solution

What is the colour for a positive biuret test?

Purple

What is the colour for a negative biuret test?

Stays blue

What does the iodine test test for?

Starch

What test determines the presence of starch?

Iodine test

Explain the iodine test for starch

• Dissolve iodine in a potassium iodide solution

• Add the solution to the test sample

What is the colour for a positive iodine test?

Blue black

What is the colour for a negative iodine test?

Stays browny-orange

What does the emulsion test test for?

Lipids

Which test determines the presence of lipids?

Emulsion test

Explain the emulsion test for lipids

• Shake the test tube with ethanol for about a minute

• Then pour the solution into water

What happens to the solution in a positive emulsion test?

Turns milky

What happens to the solution in a negative emulsion test?

Stays clear

What does the benedicts test test for?

Sugars

What test determines the presence of sugars?

Benedicts test

Why does the Benedict’s test differ?

Depends on if you’re testing for reducing or non reducing sugars

Give examples of reducing sugars

All monosaccharides e.g glucose

Some disaccharides e.g maltose/lactose

Explain the benedict’s test for reducing sugars

• Add benedict’s reagent to a sample

• Heat in a water bath thats been brought to a boil

What will happen to the solution in a positive benedict’s test for reducing sugars?

Brick red precipitate forms

What will happen to the solution in a negative benedict’s test for reducing sugars?

Stays blue

What can be tested for if theres no reducing sugars present?

Non-reducing sugars

What do you have to do before testing for non reducing sugars?

Break it down into a monosaccharide

Explain the benedict’s test for non reducing sugars

• Get a new sample of the test solution and add dilute hydrochloric acid

• Heat in a water bath thats been brought to a boil

• Neutralise it with sodium hydrogencarbonate

• Then carry out the Benedicts test for reducing sugars

What will happen to the solution in a positive benedict’s test for non-reducing sugars?

Brick red precipitate

What will happen to the solution in a negative benedict’s test for non-reducing sugars?

Stays blue

What is another way to test for glucose?

Use testing strips

Explain how to test for glucose using testing strips

• Coat the testing strips in a reagent

• Then dip the strips in a test solution

What can be used to give an indication of the conc. of glucose present

A chart

What are the glucose testing strips useful for?

Indicating wether a person has diabetes by testing their urine

What does quantitative testing determine?

The conc. of a substance present in a sample

What is used to get a quantitative estimate of glucose present in a solution?

Colorimeter and benedicts test

What is a colorimeter and what does it measure?

A device that measures the strength of a coloured solution

How does a colorimeter test the strength of a coloured solution?

By seeing how much light passes through it

Explain how to use a colorimeter to measure absorbance of an unknown solution

• Make up several solutions of known glucose concentration and measure the absorbance of them

• Plot the absorbances on a graph to make a calibration curve

• Use the calibration curve to determine the conc of glucose in the unknown solution

What is a biosensor?

A detector that uses a biological molecule e.g an enzyme to detect a chemical

What does a glucose biosensor determine?

The concentration of glucose in a solution

What does a glucose biosensor use to determine glucose?

Using the enzymes glucose oxidases and electrodes

What does the enzyme in a glucose biosensor do?

Catalyses the oxidation of glucose at the electrodes

What does the oxidation of glucose in a glucose biosensor create?

Creates a charge

What is the charge converted into and where?

Converted into an electrical signal at the transducer

What does the electrical signal then do?

Is processed to work out the initial glucose concentration