Biological molecules - Carbohydrates Flashcards
What are the roles of carbohydrates in living organisms?
Carbohydrates provide energy supply (glucose), energy stores (starch and glycogen) and structure (cellulose and chitin).
Name 3 monosaccharides.
Alpha glucose, Beta Glucose and Ribose.
Describe the structure of a monosaccharide.
A monosaccharide are simple sugars made up of only carbon, hydrogen and oxygen.
Describe how an alpha glucose differs to a beta glucose molecule.
The -OH group present on the first carbon atom of the molecule is above the plane of the ring for a beta glucose whereas it is bellow on an alpha glucose.
Explain how 2 monosaccharides join together to form a disaccharide.
Two monosaccharides join together with a glycosidic bond when a condensation reaction occurs forming a disaccharide.
Name 4 disaccharides.
- alpha glucose + alpha glucose = maltose
- alpha glucose + fructose = sucrose
- beta glucose + alpha glucose = lactose
- beta glucose + beta glucose = cellobiose
Name 4 polysaccharides and state whether they are found in a plant or animal cell.
- Amylose (in plants)
- Amylopectin (in plants)
- Glycogen (in animals)
- cellulose (in plants)
Describe the structure of amylose.
Amylose coils into a spiral shape, with hydrogen bonds holding
Describe the structure of amylose.
A long chain of alpha glucose molecules, has glycosidic bonds between carbons 1 - 4.
Amylose coils into a spiral shape, with hydrogen bonds holding the spiral in place. Hydroxyl groups on carbon 2 are situated on the inside of the coil, making the molecule less soluble and allowing hydrogen bonds to form to maintain the coils structure.
Describe the structure of amylopectin.
A long chain of alpha glucose molecules, has glycosidic bonds between carbons 1 - 4 but it also has branches that formed by glycosidic bonds between carbon 1 - 6.
Amylopectin coils into a spiral shape, held together by hydrogen bonds, with branches emerging from the spiral.
Describe the structure of glycogen.
A long chain of alpha glucose molecules, has glycosidic bonds between carbons 1 - 4 but it also has branches that formed by glycosidic bonds between carbon 1 - 6.
The 1 - 4 bonded chains tend to be smaller than in amylopectin, so glycogen has less tendency to coil. However it does have more branches, which makes it more compact. and it is easier to remove monomer units as there are more ends.
Describe the structure of cellulose.
It is a tough, insoluble and fibrous substance.
made up of up to 15000 beta glucose molecules bonded together by glycosidic bonds through condensation reaction.
Explain how you can test for starch.
The test for starch is done by adding iodine solution to a sample. If starch is present a colour change will be visible, going from yellow to blue-black.
Explain how you can test for reducing sugars.
Use the Benedict’s test. If the reducing sugar and Benedict solution is heated up there is a colour change from blue to green to yellow to orange-red .
Explain how you can test for non-reducing sugars.
For non reducing sugars, the bonds have to be hydrolysed first, to ‘free’ up these ‘reducing groups’, and then test for reducing sugars.
First check the sample for reducing sugars first. take a separate sample and boil it with hydrochloric acid to hydrolyse it to form monosaccharides. cool the solution and use sodium hydrogen-carbonate solution to neutralise it. Test for reducing sugars again.
A positive result (green-yellow-orange-red) indicates that a non-reducing sugar was present in the original sample.
