2.2.13 practical biochem 2: quantitative tests for bio molecules

Question 1

what does benedict’s reagent detect

Answer 1

presence of reducing sugars

Question 2

if more sugar present, what will happen

Answer 2

• amount of precipitate increases
• amount of copper (II) ions in solution decrease

Question 3

how can we try quantify the concentration of sugar in the original sample

Answer 3

colorimetry

Question 4

how does colorimetry work

Answer 4

by shining light through sample

Question 5

what would we use to separate precipitate & excess benedict’s solution (supernatant)

Answer 5

centrifuge

Question 6

describe steps of using a colorimeter

Answer 6

1. using pipette, take supernatant & place in cuvette then placed into colorimeter

• colour filters often used for greater accuracy
  2. using red filter (in this case), can shine light through & detect how much passes through (percentage transmission) - solution reflects blue but absorbs red

Question 7

result if lot of copper unreacted sulfate

Answer 7

supernatant still quite blue, absorption of red light is high & percentage transmission low

Question 8

result if little unreacted copper sulfate

Answer 8

supernatant less blue, absorption of red light is low & percentage transmission high

Question 9

what do we often do to the colorimeter between each reading

Answer 9

zero it by placing appropriate ‘blank’ sample to reset 100% transmission/absorption eg. water

Question 10

what result does using a colorimeter give us

Answer 10

semi-quantitative

Question 11

what do we need to find exact amount of sugar contained in each sample

Answer 11

calibration curve

Question 12

steps of creating a calibration curve

Answer 12

1. take series of known conc. of reducing sugars
2. using sample of each, do benedict’s test
3. use colorimeter to record percentage transmission of light through each supernatant
4. plot graph showing transmission of light against conc. of reducing sugar

Question 13

what can we use a calibration curve for

Answer 13

use with other ‘unknown’ samples to determine conc. of sugar in original sample

Question 14

function of biosensors

Answer 14

take biological/chemical variable, which cannot be easily measured, and convert into electrical signal

Question 15

examples of what biosensors can be used for

Answer 15

• detect contaminants in water/pathogens & toxins in food
• detect airborne bacteria eg. in counter-bioterrorism programmes