Carbohydrates

Question 1

What are carbohydrates?

Answer 1

• Carbohydrates are carbon molecules (carbo) combined with water (hydrate).
• Carbohydrates are biomolecules that are made of carbon, hydrogen and oxygen atoms.
• Carbohydrates are made from monosaccharides, which are simple sugars containing 3 to 7 carbon atoms.

Question 2

What are the jobs of Carbohydrates?

Answer 2

• Carbohydrates are used to store energy (starches), provide energy for the cells (glucose) and provide structure to plants and some animals.

Question 3

What are the 3 main types/ groups of carbohydrates?

Answer 3

• The 3 main types/groups of carbohydrates is:
• Monosaccharides (simple sugars): these are the monomers from which larger carbohydrates are made. They can’t be hydrolysed to make the simple sugars.
• Disaccharides: these are ‘double sugars’ formed from the condesation of 2 monosaccharides.
  -Polysaccharides: these are large molecules formed from many monosaccharides.

Question 4

Name the 3 hexose monosaccharides:
Hexose (6C) atoms

Answer 4

• Examples are monosaccharides are:
• Glucose
• Galactose (found in milk)
• Fructose (found in fruits).

Question 5

What is the formula for monosaccharides?

Answer 5

• C6, H12, O6.

Question 6

What is glucose?

Answer 6

• Glucose is a hexose sugar that has the chemical formula C6,H12,O6.
• Glucose is an important source of energy in humans. As during cellular respiration, the energy released from glucose helps to make ATP.

Question 7

What are the two types of Glucose?

Answer 7

• There are two types of Glucose:
• Alpha glucose
• Beta glucose
  These are isomers. Isomers have the same molecular formula but a different arrangements of atoms in the molecule.

Question 8

What is the difference between the Alpha glucose and the beta glucose?

Answer 8

The difference between the alpha glucose and the beta glucose is that:
- The alpha glucose hydroxyl group (OH) is at the bottom and the hydrogen atom is at the top bonded to carbon 1.
- Whereas in the beta glucose. the hydroxyl (OH) group is at the top and the hydrogen atom is at the bottom bonded to carbon 1.

Question 9

Name the 3 types of disaccharides and how they are formed?
Disaccharides are ‘double sugars’ which are formed by the condensation of 2 monosaccharides.

Answer 9

The 3 disaccharides are:
- Maltose: formed by the condensation of glucose + glucose.
- Sucrose: formed by the condensation of glucose+fructose.
- Lactose: formed by the condensation of glucose + galactose.

Question 10

Name the enzymes that are needed to catalyse the break down of the disaccharides (maltose, sucrose and lactose):

Answer 10

The enzymes that are needed to catalyse the break down of the disaccharides:
- Maltose= the enzyme = maltase
- Sucrose= the enzyme= sucrase
- Lactose= the enzyme= lactase

Question 11

What is the formula for disaccharides?

Answer 11

• C12, H22, O11.

Question 12

Test for reducing sugars: (benedict’s test)
All monosaccharides and some disaccharides (e.g. maltose and lactose) are reducing sugars. reduction is a chemical reaction involving the gaining of electrons or hydrogen. A reducing sugar is therefore a sugar that can donate electrons to (or reduce) another chemical, in this case Benedict’s reagent.

Answer 12

Benedict’s reagent is an alkaline solution of copper (II) sulfate.
1) you add 2cm^3 of the food sample to be tested to a test tube. If the sampe is not already in liquid form, first grind it up in water.
2) Add an equal volume of Benedict’s reagent to the sample.
3) Heat the mixture in a hot water bath for 5 mins.
If the tests positive it will form a brick red preciptate. As the higher the concentration of reducing sugar, the further the colour changes, as it goes from:
blue -> green -> yellow -> orange -> Brick red precipitate. A more accurate way of doing this is to filter the solution and weigh the precipitate.

Question 13

Tests for non-reducing sugar:

Answer 13

• If the results of the reducing sugars test is negative (remain blue), there could still be a non-reducing sugar present.
  To test for non-reducing sugars (e.g. sucrose), first you have to break them (disaccharides) down into monosaccharides.
• You do this by getting a new sample of the test solution, adding 2cm^3 of dilute hydrochloric acid and heat in a hot water bath.
• Then you neutralise it with sodium hydrogencarbonate. Then you carry out the benedicts test as you would for reducing sugar.
• If the test’s positive, it has non-reducing sugars present) , it will form a coloured precipitate (orange/brown) (as for the reducing sugars test). If the tests negative the solution, will remain blue, indicating it doesnt contain any sugar (either reducing or non-reducing).

Question 14

What are polysaccharides?

Answer 14

-Polysaccharides are polymers formed by combining together many monosaccharide molecules. The monosaccharide are joint together by glycosidic bonds that were formed by condesnation reactions.

Question 15

What makes polysaccharides suitable for storage?

Answer 15

• Due to polysaccharides being large molecules making them insoluble, this feature enables them to be suitable for storage.

Question 16

What happens to the polysaccharides, when they are being hydrolysed (broken down)?

Answer 16

• When the polysaccharides are being hydrolysed, they either break down into disaccharides or monosaccharides.

Question 17

Name the 3 polysaccharides:

Answer 17

• The 3 polysaccharides are:
• Starch
• Glycogen
• Cellulose

Question 18

What storages are formed by the condensation of Alpha glucose?

Answer 18

• Starch
• Glycogen.

Question 19

How is starch formed by the condensation of Alpha glucose?

Answer 19

• Starch is formed by the condensation of alpha glucose because lots of alpha glucose molecules joined together by glycosidic bonds to form amylose.