Biochemical Tests and Separating Molecules (pages 32 - 33) Flashcards
What do Biosensors detect?
Biosensors can detect chemicals in a solution.
What is a Biosensor?
it is a device that uses a biological molecule, such as an enzyme (see page 42) to detect a chemical.
How do the biosensor work to detect a chemical?
the biological molecule produces a signal (e.g. a chemical signal), which is converted to an electrical signal by a transducer (another part of the biosensor).
The electrical signal is then processed and can be used to work out the other information.
Give an example how a biosensor can determine the concentration of glucose in a solution?
1) A glucose biosensor is used to determine the concentration of glucose in a solution.
2) it does this by using the enzyme glucose oxidase and electrodes
3) the enzyme catalyses the oxidation of glucose at the electrodes - this creates a charge, which is converted into an electrical signal by the electrodes (the transducer).
4) The electrical signal is then processed to work out the initial glucose concentration.
What is Chromatography used for?
to separate stuff in a mixture - once it’s separated out, you can often identify the components.
for examples, chromatography can be used to separate out and identify biological molecules such as amion acids, carbohydrates, vitamins and mucleic acids.
There are quite a few different types of chromatography - you only need to know about paper chromatography and thin-layer chromatography.
How do chromatography work? (you need to understand this).
1) All types of chromatography (including paper and thin-layer) have the same basic set up:
1a) A mobile Phase - where the molecules can move. in both paper and thin-layer chromatography the mobile phase is a liquid solvent, such as ethanol or water.
1b) A Stationary Phase - where the molecules can’t move:
In paper chromatography the stationary phase is a piece of chromatography paper.
In the thin-layer chromatography the stationary phase is a thin (0.1 - 0.3 mm) layer of solid, e.g. silica gen, on a glass or plastic plate.
2) And they all use the same basic principle:
2a) the mobile phase moves through or over the stationary phase
b) the components in the mixture spend different amounts of time in the mobile phase and the stationary phase.
c) the components that spend longer in the mobile phase travel faster or further.
d) the time spent in the different phases is what separates out the components of the mixture.
look at diagram 1 on page 32.
What is Paper Chromatography used to identify?
it is used to identify unknown Amion Acids.
(in the exam you might be asked how chromatography can be used to identify biological molecules in a mixture)
Give an example of how paper chromatography can be used to identify Amino acids in a mixture?
(if you’re trying to identify different biological molecules, the method will vary slightly (e.g. a different solvent might be used) but the basic principle will be the same).
1) draw a pencil line near the bottom of a piece of chromatography paper and put a concentrated spot of the mixture of amino acids on it. It’s best to carefully roll the paper into a cylinder with the spot on the outside so it’ll stand up.
2) Add a small amount of prepared solvent (a mixture of butan-1-of glacial ethanoic acid and water is usually used for amion acids) to a beaker and dip the bottom of the paper into it (not the spot). This should be done in a fume cupboard. Cover with a lid to stop the solvent evaporating.
3) as the solvent spreads up the paper, the different amino acids (solutes) move with it, but at different rates, so they separate out.
4) When the solvents nearly reached the top, take the paper out and mark the solvent front with pencil. then you can leave the paper to dry out before you analyse it.
5) Amino acids aren’t coloured, which means you won’t be able to see them on the paper. So before you can analyse them, you have to spray the paper with ninhydrin solution to turn the amino acids purple. This shold also be done in a fume cupboard and gloves should be worn. (note: you cant use ninhydrin to detect all biological molecules, only proteins and amino acids).
6) You can then use R, values to identify the separated molecules:
and R, value is the ratio of the distance travelled by a solute to the distance travelled by the solvent. You can calculate it using the formala
distance travelled by solute R value of amion acid = \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
distance travelled by solvent.
When you’re measureing how far a solute has travelled, you measure from the point of origin to the vertical centre of the spot.
you can work out what was in a mixture by calculating an R, value for each solute and looking each R, value up in a database, or table, of known values.
(you could also compare your chromatogram to the chromatogram of a known mixture and identify the components that way - if two solutes have travelled the same didtance in the solvent, they will be the same molecule).
see diagram 1 on page 33.
What is a biosenor?
A biosensor is a device that uses a biological molecule, such as an enzme to detect a chemical.
What is Chromatography used for?
it is used to identify unknown amino acids.
Why would you use ninhydrin solution when using chromatography to identify amino acids in a mixture?
Amino acids aren’t coloured, which means ou won’t be able to see them on the paper. So before you can analyse them you have to spray the paper with ninhydrin solution to turn the amino acids purple. (this should also be done in a fume cupboard and gloves should be worn, also note, you cant use ninhydrin to detect all biological molecules, only proteins and amino acids).
The pepr chromatogram on page 33, shows the separation of three sugars from a solution.
a) briefly describe the method used to produce this chromatogram (3 marks)
b) explain why the solutes have ended up in different positions on the chromatogram (1 mark)
c) calculate thr Rf value of solute X and use your answer to identify which sugar it is (3 marks)
a) A concentrated spot of the sugar solution was placed on the line at the bottom of the paper (1 mark). The botto of the paper was then dipped in a solvent (1 mark). The paper was taken out when the solvent had nearly reached the top of the paper (1 mark)
b) The substances in the sugar solution travel different distances in the mobile phase (1 mark)
c) distance travelled by solute
Rf value = ________________________________
distance travelled by solvent.
= 2.5 ÷ 10.4 cm = 0.24 [2 marks for 0.24 or 1 mark for the correct calculation]
Solute X is fructose [1 mark]
fructose has a Rf value of 0.24 in the table of Rf values, so solute X is fructose.
