Topic 1---A:Biological molecules- 2. Sugars Flashcards
What is sugar a general term for?
Monosaccharides and disaccharides.
What are monosaccharides?
They are the simplest sugars and are the building blocks of carbohydrates.
What elements does carbohydrates contain?
- Carbon
- Hydrogen
- Oxygen
What are the monomers carbohydrates are made from?
Monosaccharides
e.g.
- Glucose
- Fructose
- Galactose
What is glucose?
- It’s a hexose sugar
- A monosaccharide with 6 carbon atoms in each molecule.
- There are two types of glucose (alpha and beta glucose).
What are alpha and beta glucose?
They’re isomers
What are isomers?
They are molecules with the same molecular formula as eachother, but with atoms connected in a different way.
What is the difference between alpha and beta glucose?
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.
How is a disaccharide formed?
- Disaccharides are formed when two monosaccharides join together.
- Monosaccharides are joined together by condensation reactions.
What bond is formed between the two monosaccharides as a molecule of water is released in the condensation reaction?
A glycosidic bond
How is sucrose formed?
- Sucrose is a disaccharide formed from a condensation reaction of a glucose molecule and a fructose molecule.
How is maltose formed?
- Maltose is a disaccharide formed from a condensation reaction of two glucose molecules.
How is lactose formed?
- Lactose is a disaccharide formed by a condensation reaction of a glucose molecule and galactose molecule.
How can sugars be classified and tested?
- Sugars can be classified as reducing sugars or non-reducing sugars.
- To test for sugars you use the Benedict’s test.
What examples are there of reducing sugars?
- All monosaccharides and some disaccharides.
E.g. - Glucose
- Fructose
- Galactose
- Maltose
- Lactose
Reducing sugars
- 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.
Non-reducing sugars
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.
What is an example of a non-reducing sugar?
Sucrose
How is the benedicts solution supply us with semi-quantitative data?
By seeing the colours of solution and precipitate you can tell the concentration/ strength of the reducing sugar.
