practical bio-chem 1 : quantitative tests for biological molecules

Question 1

how do you calibrate a colorimeter ?

Answer 1

• turn on colourimeter
• set colourimeter to coloured filter and absorbance or transmission
• 3/4 fill a cuvette with distilled water
• place cuvette into colourimeter and zero for absorbance or 100 % transmission

Question 2

what ions are reduced in the benedict’s reducing sugar test ?
–> what colour do they change from and to ?

Answer 2

Cu 2+ (blue ions) are reduced to Cu+ (red ions)

Question 3

what does quantitative data mean ?

Answer 3

• provides number-based data

Question 4

what does benedict’s reagent detect ?

Answer 4

• presence of reducing sugars

Question 5

what happens if more sugar is present ?

Answer 5

• the amount of precipitate will increase
• the amount of copper (ii) ions remaining in the solution will decrease

Question 6

how can one quantify the concentration of sugar ?

Answer 6

• by assessing how the 2 variables change using a technique called colourimetry

Question 7

how does a colorimeter work ?

Answer 7

• by shining light through a sample

Question 8

what would be a centrifuge be used for ?

Question 9

what should one ensure when using a cuvette because.. ?

Answer 9

• ensure you don’t leave a greasy fingerprint on the surface of the cuvette
  –> as it could affect transmission of light

Question 10

what are colour filters used for ?

Answer 10

• greater accuracy
  using red filter –> shines red light through the solution
  –> detects how much passes through
  –> solution reflects blue light but absorbs red light

Question 11

what is a supernatant ?

Question 12

what happens to the transmission and absorption of light when there is lots of Cu2+ ions in solution ?

Answer 12

• low transmission of light
• absorption of red light is high

Question 13

what happens to the transmission and absorption of light when there is little unreacted Cu2+ ions in solution ?

Answer 13

• high transmission of light
  -absorption of red light is low

Question 14

what is the purpose of calibiration curve

Answer 14

to find exact amounts

Question 15

how can one create a calibration curve ?

Answer 15

1. first take a series of known concentrations of reducing sugar
2. using a sample of each , carry out benedict’s test
3. use a colorimeter to record the percentage transmission of light through each supernatant
4. plot a graph to show ‘transmission of light’ against the concentration of reducing sugar
   –> this provides a calbiration curve , which you can use with other ‘unknown’ samples to determine the concentration of sugar in the original sample

Question 16

what are biosensors used for ?

Answer 16

• they take biological or chemical variables which cannot easily be measured and covert it in to an electrical signal

Question 17

draw a diagram of how biosensors work

Answer 17

in the textbook :)

Question 18

what can biosensors also be used for ?

Answer 18

• used to detect contaminants in water and pathogens and toxins in food
• used to detect airborne bacteria

Question 19

explain why the transmission of red light increases as the glucose concentration in the sample rises

Answer 19

• more glucose means more reduction of Cu2+ to Cu1+ which means less dissolved Cu2+
  –> this means less intensity of blue colouration which in turn indicates that more red light is transmitted

Question 20

why is it necessary to centrifuge the sample before taking colorimeter readings ?

Answer 20

the perciptate must be removed from the sample before colourimetery because any suspended particles will scatter light creating a false low transmission reading