Carbohydrates Flashcards

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1
Q

What is the basic monomer unit of a carbohydrate?

A

A sugar, known as a saccharide.

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2
Q

How are carbohydrates built?

A

Many monosaccharides are paired up by condensation reaction (removal of water) to form a disaccharide, joined by a glycosidic bond.

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3
Q

What are monosaccharides?

A

Sweet tasting, soluble substances with the general formula (CH2O)n, with n being between 3-7.

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4
Q

Test for reducing sugars

A
  • Add sample to a test tube, in liquid form or ground up in water.
  • Add equal volume of Benedict’s Reagent.
  • Gently heat in boiling water bath for 5 mins.
  • If reducing sugar is present, solution turns orange-brown.
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5
Q

What are reducing sugars?

A

All mono and some disaccharides. Reducing sugar is able to donate electrons (reduce) another chemical.

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6
Q

What is Benedict’s Reagent?

A

Alkaline solution of Copper II Sulphate. Forms an insoluble red precipitate of Copper I Oxide when heated with reducing sugar.

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7
Q

What happens when water is added to a disaccharide?

A

Glycosidic bond breaks, releasing monosaccharides, in hydrolysis reaction.

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8
Q

What are disaccharides?

A

Pairs of monomers joined.

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9
Q

What happens with non-reducing sugars, e.g. sucrose?

A

They do not change colour of Benedict’s Reagent when they are heated with it, so must be hydrolysed into monosaccharides.

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10
Q

Test for non-reducing sugars

A
  • Solution remains blue after initial test.
  • Add another equal amount of dilute HCl and Sample to test tube and heat it.
  • Slowly add sodium hydrogencarbonate solution to neutralise HCl (test with pH paper to check alkaline).
  • Repeat Benedict’s test, solution should now turn orange/brown.
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11
Q

Why does the solution at the end of the test for non-reducing sugars go brown?

A

Reducing sugars were produced from the hydrolysis of the non-reducing sugar when HCl was added.

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12
Q

What are polysaccharides?

A

Polymers formed by combining many monosaccharide molecules by glycosidic bonds from condensation reactions.

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13
Q

Why is it advantageous for polysaccharides to be large molecules?

A

They are suitable for storage, e.g. starch and glycogen.

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14
Q

Test for Starch

A
  • Add sample to a test tube or spotting tile.
  • Add 2 drops of iodine and shake or stir.
  • Presence of starch is indicated by a blue-black coloration.
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