Topic 1a- Biological Molecules- Carbohydrates Flashcards
Carbohydrates
Maltose is a sugar. Describe how a molecule of maltose is formed.
Two molecules of alpha-glucose are joined by glycosidic bonds. A molecule of water is released a condensation reaction takes place.
What is a condensation reaction and what is a monosaccharide.
A condensation reaction is when two molecules join together with the formation of a new chemical bond, and a water molecule is released when the bond is formed.
Monosaccharides are joined together by condensation reactions.
What is a glycosidic bond?
Forms between two monosaccharides as a molecule of water is released.
What is sucrose and lactose?
Sucrose- a disaccharide formed from a condensation reaction between a glucose molecule and a fructose molecule.
Lactose- another disaccharide formed from a glucose molecule and a galactose molecule.
What is a hydrolysis reaction?
Breaks the chemical bond between monomers using a water molecule. The opposite of a condensation reaction.
Use Benedict’s Test for sugars. What is the reducing sugars practical?
- Include all monosaccharides and some disaccharides.
- Add Benedict’s reagent to a sample and heat it in a water bath that’s been brought to the boil.
- If test’s positive it will form a coloured precipitate.
- The higher the concentration of reducing sugar, the further the colour change goes- you can use this to compare the amount of reducing sugar in different solutions.
What is the practical for non-reducing sugars?
- If negative, could still be a non-reducing sugar present. To test for non-reducing sugars, like sucrose, first you have to break them down into monosaccharides.
- Get a new sample of test solution, adding dilute hydrochloric acid and carefully heating it in a water bath, been brought to the boil.
- Then neutralise it with sodium hydrogencarbonate. Then carry out Benedict’s test as you would for reducing sugar.
- If positive forms a coloured precipitate. If negative solution will stay blue, means it doesn’t contain any sugar.
What is starch?
A mixture of two polysaccharides of alpha-glucose- amylose and amylopectin. Starch is the main energy storage in plants. Use iodine test for starch.
What is amylose and amylopectin?
Amylose- a long, unbranched chain of a-glucose. Angles of the glycosidic bonds give it a coiled structure. Makes it compact- good for storage.
Amylopectin- a long, branched chain of a-glucose. Side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily. Means that glucose can be released quickly.
What is glycogen?
The main energy storage material in animals. It’s structure is very similar to amylopectin, except that it has loads more side branches coming off it. Loads of branches means that stored glucose can eb released quickly, which is important for energy release in animals. Compact so it’s good for storage.
What is cellulose?
Major component of cell walls in plants. Made of long, unbranched chains of beta-glucose. When beta-glucose molecules bond, they form straight cellulose chains. They are linked together by hydrogen bonds to form a strong fibres called microfibrils.
The strong fibres mean cellulose provides structural support for cells.
Hydrogen bonds are important in cellulose molecules. Explain why.
Hydrogen bonds are strong in large numbers. Provides strength for the molecule as there is lots of them.
A starch molecule has a spiral shape. Explain why this shape is important to its functions in cells.
It coils up making it more compact so it can store more in a tight space.
Describe 2 ways in which molecules of cellulose are similar to molecules of starch.
- Both insoluble
- Both contain glycosidic bonds
