Biochemical Tests for Molecules Flashcards

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1
Q

Starch

Iodine test

A
  • add iodine dissolved in potassium iodide solution to test sample
  • if starch is present, brown/orange to dark blue/black
    no starch, stays brown/orange
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2
Q

Protein

Biuret test

A
  • test solution needs to be alkaline so add few drops of sodium hydroxide solution
  • add some copper (ii) sulphate solution
  • if protein present (positive result), turns pale purple
  • no protein (negative result), stays pale blue
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3
Q

Lipid

Emulsion test

A
  • shake test sample with ethanol for about 1 minute then pour solution into water
  • if lipid is present, solution turns milky
  • more lipid, more noticeable the milky colour is
  • no lipid, solution stays clear
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4
Q

Glucose

Test strips

A
  • glucose tested using test strips coated in a reagent
  • strips dipped in test solution and change colour if glucose is present
  • colour change compared to chart to give indication of the concentration of glucose present
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5
Q

why are glucose test strips useful?

A
  • useful to test a person’s urine for glucose to indicate if person has diabetes
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6
Q

reducing sugar

Benedicts test

A
  • reducing sugars include all monosaccharides and some disaccharides
  • add Benedicts reagent (blue) to sample and heat it in water bath that’s been brought to boil
  • colour of precipitate changes from:
    blue - green - yellow - orange - brick red
  • if positive result, forms coloured precipitate
  • higher the concentration of reducing sugar, further the colour change goes (used to compare amount of reducing sugars in different solutions)
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7
Q

what is a more accurate method to compare the amount of reducing sugars in different solutions?

A

filter the solution and weigh the precipitate

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8
Q

Non-reducing sugars

Benedicts test

A
  • if negative result for reducing sugar then non-reducing sugar may be present
  • firstly, have to break non-reducing sugars to monosaccharides
  • add dilute HCL to new test sample and heat in water bath that’s been brought to boil
  • neutralise with sodium hydrogencarbonate and carry out benedicts test
  • positive result, forms coloured precipitate
  • negative result, stays blue so no sugar present
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