tests for biological molecules Flashcards
How would you carry out the biuret test for proteins? (4)
- Add sodium hydroxide to make the solution alkaline;
- Add copper (II) sulfate solution;
- Protein present: solution turns purple;
- No protein: solution stays blue
How would you carry out the benedict’s test for reducing sugars? (4)
- Add Benedict’s reagent to the sample;
- Heat in a water bath;
- Reducing sugar present: coloured precipitate forms (green to brick red);
- No reducing sugar: stays blue
How would you carry out the benedict’s test for non-reducing sugars? (4)
- Add dilute hydrochloric acid and heat to hydrolyse your sample;
- Neutralise acidic solution with sodium hydrogen-carbonate;
- Redo Benedict’s test;
- Positive: coloured precipitate. Negative: stays blue
What are reagent test strips used for? (3)
To detect reducing sugars like glucose;
Dip strip into the test solution;
Color change indicates sugar presence
How would you carry out the iodine solution for starch? (3)
- Add potassium iodide solution to the sample.;
- Starch present: solution turns blue-black.;
- No starch: remains browny-orange
How would you carry out the emulsion solution for lipids? (3)
- Shake the test substance with ethanol.;
- Pour into water;
- Lipid present: solution turns milky. No lipid: stays clear
What does a colorimeter measure? (2)
Measures the absorbance of a coloured solution;
The more concentrated the solution, the higher the absorbance
How do you zero a colorimeter? (1)
Use a cuvette containing a blank (water)
How do you create a calibration curve for glucose concentration? (3)
- Make serial dilutions of glucose;
- Add Benedict’s solution to each, filtering out the precipitate;
- Measure the absorbance of the remaining solution with a colorimeter
How does glucose concentration affect absorbance in a colorimetry test? (2)
Higher glucose concentration = lower absorbance of the remaining solution
How do you determine an unknown glucose concentration using a calibration curve? (2)
- Test the unknown solution with Benedict’s solution;
- Use the calibration curve to find its concentration based on absorbance
What is a biosensor and how does it work? (3)
Uses a biological molecule (e.g., enzyme) to detect a chemical;
Produces a chemical signal, converted to an electrical signal by a transducer;
The electrical signal is processed
How does a glucose biosensor work? (3)
- Enzyme glucose oxidase catalyses glucose oxidation at electrodes;
- This creates a charge, which is converted into an electrical signal by the transducer;
- The signal is processed to determine glucose concentration
What is the mobile phase in chromatography? (2)
Phase where molecules can move;
The mobile phase in paper and thin-layer chromatography is a liquid solvent (e.g., ethanol or water)
What is the stationary phase in chromatography? (3)
Phase where molecules can’t move;
In paper chromatography, this is the chromatography paper;
In thin-layer chromatography, this is the thin layer of gel on a glass/plastic plate
What separates components in a mixture during chromatography? (1)
Components that spend more time in the mobile phase travel further
How do you set up paper chromatography for amino acids? (4)
- Draw a pencil line at the bottom of the paper;
- Spot the mixture of amino acids on the line (point of origin);
- Dip the bottom of the paper in solvent;
- As solvent spreads up the paper, amino acids separate based on solubility
How do you visualise amino acids after chromatography? (1)
Spray the paper with ninhydrin solution to turn the amino acids purple
How do you calculate an Rf value in chromatography? (2)
- Rf = distance travelled by spot / distance travelled by solvent;-
Measure from the point of origin to the centre of the spot
How can you identify compounds using chromatography? (2)
Compare Rf values to a known database;
Compare your chromatogram to a known mixture to identify compounds
What can chromatography distinguish between in sugars? (2)
Between reducing sugars like glucose and fructose;
Unlike Benedict’s test
