Biochemical tests Flashcards

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1
Q

what are the 3 different carbohydrates that you need to know the tests for ?

A
  • starch
  • reducing sugars
  • non-reducing sugars
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2
Q

what are the 3 categories of biochemical tests that you need to know ?

A
  • carbohydrates
  • proteins
  • lipids
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3
Q

test for starch

A
  • add the potassium iodide solution ( reagant)
  • positive test = solution turns from orange to blue/black
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4
Q

test for reducing sugars ?

A
  • add benedict’s reagent and heat
  • a positive test observation = turns from blue to green, yellow, orange or brick red
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5
Q

what does it mean if the benedict’s reagent turns more red ?

A

the more red the solution is, the higher the concentration of the reducing sugar
green means it has a low conc of reducing sugars

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6
Q

why does the colour change occur at the top of the solution first ?

A

because of convection current as the hottest particles will rise to the top and they will have the most kinetic energy and more successful collisions so the reaction will occur the fastest at the top

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7
Q

test for non reducing sugars: what do you have to do before you peform the non reducing sugars test ?

A

firstly you have to confirm that the sample is not a reducing sugar by doing the benedict’s test
so a negative result will mean that the reagent remains blue

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8
Q

test for non reducing sugars: ? (sucrose)

A
  • add an acid and boil for 2 mins - to perform acid hydrolysis
  • cool solution and add an alkali to neutralise it
  • add benedict’s reagent and heat
  • positive test observation = turns from blue to green, yellow, orange or brick red
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9
Q

what will happen due to the fact you boil the non reducing sugar with acid ( acid hydrolysis ) ?

A

this will break the glycosidic bonds and cause sucrose to be hydrolysed and become glucose and fructose

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10
Q

state all the reducing sugars
?

A

all of the monosacharrides :
- glucose
- fructose
- galactose
and 2 of the disacharrides :
- maltose
- lactose

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11
Q

state the non-reducing sugar ?

A

sucrose

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12
Q

what is meant by a reducing sugar ?

A

these sugars can reduce the copper sulphate (blue) in benedict’s reagent to copper oxide (brick red)

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13
Q

what is meant by a non-reducing sugar ?

A

the reducing group is involved in the glycosidic bond in sucrose and therefore sucrose cannot reduce copper sulphate to copper oxide

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14
Q

what happens when sucrose is hydrolysed (through boiling with an acid ) ?

A

the glycosidc bond is broken and therefore the reducing group becomes exposed
a positive test is then received with benedict’s reagent following hydrolysis

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15
Q

test for proteins ?

A
  • add biuret
  • a positive test observation = solution turns from blue to purple / lilac
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16
Q

test for lipids ?

A
  • dissolve the sample in ethanol
  • add distilled water and shake
  • a positive test = a white cloudy emulsion forms