Biochemical Test for Molecules Flashcards
What is a reducing sugar?
A sugar that acts as a reducing agent because of its aldehyde or ketone group. Examples: all monosaccharides and some disaccharides (e.g., maltose, lactose).
How do you test for reducing sugars?
- Add Benedict’s reagent to the sample.
- Heat the mixture in a water bath.
- Observe the color change:
Blue → No reducing sugar.
Green/yellow → Low concentration.
Orange/brick red → High concentration.
What do green/yellow/orange/brick red precipitates indicate in a Benedict’s test?
The presence of reducing sugar, with colour intensity increasing with concentration.
What does a negative Benedict’s test indicate?
The sample may contain a non-reducing sugar (e.g., sucrose).
How do you test for non-reducing sugars?
Hydrolyse the sample by boiling with hydrochloric acid (breaks glycosidic bonds).
Neutralise the solution using sodium hydrogen-carbonate.
Perform the Benedict’s test again.
Positive result (colour change) indicates non-reducing sugar was present.
Why does the hydrolysis step in the non-reducing sugar test work?
It breaks sucrose into glucose and fructose, which are reducing sugars that give a positive Benedict’s test.
What is starch?
Starch is the storage carbohydrate in plant cells.
What reagent is used to test for starch?
Iodine dissolved in potassium iodide solution.
How do you perform a starch test?
Add iodine dissolved in potassium iodide solution to the sample.
Observe any colour change.
What is a positive result for starch?
The solution changes from orange/brown to blue/black.
Which type of cells typically contain starch?
Plant cells, such as those in potatoes.
What is the Emulsion test used for?
The Emulsion test is used to detect the presence of lipids in a sample.
How do you perform the Emulsion test for lipids?
Add ethanol to the sample and shake thoroughly.
Add an equal volume of water to the mixture.
What indicates a positive result for lipids in the Emulsion test?
A milky white suspension forms if lipids are present.
What does it mean if the solution remains colorless in the Emulsion test?
No lipids are present in the sample.
What is the Biuret test used for?
The Biuret test is used to detect the presence of proteins in a sample.
What reagents are used in the Biuret test?
Sodium hydroxide (NaOH) and copper sulfate (CuSO₄) are used, together known as Biuret reagent.
How do you perform the Biuret test for proteins?
Add sodium hydroxide to the sample.
Add copper sulphate solution.
Observe the colour change.
What indicates a positive result for proteins in the Biuret test?
A colour change from blue to purple indicates the presence of proteins.
What does a blue colour in the Biuret test indicate?
A negative result, meaning no proteins are present.
What is a biosensor?
A biosensor is an analytical device used to detect the presence of a chemical by using biological molecules to produce a chemical signal, which is then converted into an electrical signal by a transducer.
How does a biosensor work?
Biological molecules detect the chemical of interest.
The chemical reaction produces a signal.
The signal is converted into an electrical signal by a transducer.
The electrical signal is processed to determine the concentration of the chemical.
What is an example of a biosensor?
A glucose biosensor, used to measure glucose concentration in a solution.
How does a glucose biosensor work?
HINT: Good Elephants Taste Everything
G = Glucose oxidase (enzyme) catalyses oxidation
E = Electrons are created (oxidation creates charge at electrodes)
T = Transducer (electrodes convert charge into signal)
E = Electrical signal processed to determine glucose concentration
