Topic 1---A:Biological molecules- 2. Sugars

Question 1

What is sugar a general term for?

Answer 1

Monosaccharides and disaccharides.

Question 2

What are monosaccharides?

Answer 2

They are the simplest sugars and are the building blocks of carbohydrates.

Question 3

What elements does carbohydrates contain?

Answer 3

• Carbon
• Hydrogen
• Oxygen

Question 4

What are the monomers carbohydrates are made from?

Answer 4

Monosaccharides
e.g.
- Glucose
- Fructose
- Galactose

Question 5

What is glucose?

Answer 5

• It’s a hexose sugar
• A monosaccharide with 6 carbon atoms in each molecule.
• There are two types of glucose (alpha and beta glucose).

Question 6

What are alpha and beta glucose?

Answer 6

They’re isomers

Question 7

What are isomers?

Answer 7

They are molecules with the same molecular formula as eachother, but with atoms connected in a different way.

Question 8

What is the difference between alpha and beta glucose?

Answer 8

The two types of glucose have there groups reversed on the right side.
a-glucose has H at the top then OH at the bottom.
b-glucose has OH at the top and H at the bottom.

Question 9

How is a disaccharide formed?

Answer 9

• Disaccharides are formed when two monosaccharides join together.
• Monosaccharides are joined together by condensation reactions.

Question 10

What bond is formed between the two monosaccharides as a molecule of water is released in the condensation reaction?

Answer 10

A glycosidic bond

Question 11

How is sucrose formed?

Answer 11

• Sucrose is a disaccharide formed from a condensation reaction of a glucose molecule and a fructose molecule.

Question 12

How is maltose formed?

Answer 12

• Maltose is a disaccharide formed from a condensation reaction of two glucose molecules.

Question 13

How is lactose formed?

Answer 13

• Lactose is a disaccharide formed by a condensation reaction of a glucose molecule and galactose molecule.

Question 14

How can sugars be classified and tested?

Answer 14

• Sugars can be classified as reducing sugars or non-reducing sugars.
• To test for sugars you use the Benedict’s test.

Question 15

What examples are there of reducing sugars?

Answer 15

• All monosaccharides and some disaccharides.
  E.g.
• Glucose
• Fructose
• Galactose
• Maltose
• Lactose

Question 16

Reducing sugars

Answer 16

• Add benedicts reagent (blue) to a sample
• Heat in a water bath that has been brought to a boil
• A colour change to red is observed when reducing sugar is present.

Question 17

Non-reducing sugars

Answer 17

If the result of the reducing sugar is negative, there could still be a non-reducing sugar present.
- New sample
- Boil in acid to hydrolyse bonds (dilute hydrochloric acid)
- Neutralise acid with alkali (sodium hydrogencarbonate)
- Heat with benedicts reagant
- If brick red, sample contained a non-reducing sugar.

Question 18

What is an example of a non-reducing sugar?

Answer 18

Sucrose

Question 19

How is the benedicts solution supply us with semi-quantitative data?

Answer 19

By seeing the colours of solution and precipitate you can tell the concentration/ strength of the reducing sugar.