Carbohydrates Flashcards
What is the formula for monosaccharides?
Cn (H2O)n
What are the examples of Triose?
Pyruvate and glyceraldehyde
What are the examples of pentose?
Ribose and deoxyribose
What is the difference between ribose and deoxyribose’s structures?
Deoxyribose has 1 less oxygen (thus deoxy = loss of oxygen)
What are the examples of hexose?
Glucose, fructose and galactose
What is the difference between alpha and beta glucose?
The oxygen and hydroxide molecules on C1 are switched with OH at the top in beta glucose (‘bouncing’ beta)
What is a structural isomer?
Where molecules have the same formula but different structure
What the three key properties of fructose?
- it is the main sugar in fruits/nectar
- very soluble
- sweeter than glucose
What are the three key properties of galactose?
- important in glycolipid and glycoprotein production
- less soluble
- not as sweet as fructose
What is the test for monosaccharides and what is it called?
The reducing sugars test.
- mix the test solution with an equal volume of Benedict’s solution
- heat (70oC)
- a positive test result is shown by the solution turning from blue to red
What are disaccharides?
2 monosaccharides bonded by a glycosidic bond
What type of reaction is the bond formation called and why?
Condensation reaction because water is released
What the monosaccharides in maltose?
2 alpha glucose
What are the monosaccharides in sucrose?
Alpha glucose and fructose
What are the monosaccharides in lactose?
Beta glucose and galactose
Where is maltose found?
Malt sugar
Where is sucrose found?
Cane sugar
Where is lactose found?
Milk sugar
What is hydrolysis’ purpose in relativity to carbohydrates?
It is the splitting of the glycosidic bond by the chemical addition of a water molecule.
It enables disaccharides to be broken back down into mono (e.g in digestion)
How can hydrolysis be increased?
Addition of acid and heat
Enzymes
How does the non-reducing sugars (disaccharide) test work?
- add 2cm^3 to test tube
- add 10 drops HCl (1 mol)
- mix and heat (70oC)
- neutralise with alkali (sodium hydrogen carbonate)
- add 2cm^3 Bendict’s
- mix + heat
- change from blue to red = positive
What is the main use of starch?
Main storage polysaccharide in plants
What is the main use of glycogen?
Main storage polysaccharide in liver and muscles
What is the main use of cellulose?
Main structural polysaccharide in plants
What is the main use of chitin?
Main structural polysaccharide in insects
What are polysaccharides?
Polymers made up of many monosaccharides joined by glycosidic bonds
What polysaccharide group does alpha glucose contribute to?
Storage
What polysaccharide group does beta glucose contribute to?
Structure
What is amylose’s structure and why is it good for glucose storage?
Un-branched long chain of alpha glucose with 1-4 bonds. The bond angles cause it to bend into a compact coiled helix which makes it really good for glucose storage.
What is amylopectin’s structure and why is it good for glucose storage?
Long branched chain with some 1-4 bonds but many more 1-6 that give it its branches. This enables easy access for enzymes to break down glycosidic bonds and release glucose.
What percentage of starch is amylose?
20%
What percentage of starch is amylopectin?
80%
Why is starch and glycogen being insoluble beneficial?
It is a large molecule so it can’t leave the cell via the membrane and has no osmotic effect (doesn’t draw water into the cell)
What is the test for starch?
Mix test solution with 3 drops of iodine solution. A change from orange to blue/black = positive result.
What is glycogen’s structure?
Similar to amylopectin but with many more 1-6 bonds leading to more side branches
What is the effect of glycogen’s many branches?
Stored glucose can be released quickly
What is glycogen easily hydrolysed by?
Glycogen phosphorylase, an enzyme, to provide glucose for respiration
How is cellulose structured?
Many beta glucose units linked by 1-4 glycosidic bonds forming long straight chains. Every other molecule rotates 180o so the hydroxyl (OH) groups line up. The alternating up and down bonds increases structural strength. The chains are cross linked by 3-6 hydrogen bonds.
What is formed by the chains grouping in cellulose?
Strong fibres called microfibrils which make plant walls inelastic through their arrangement, giving strength and rigidity and preventing bursting when taking in excess water.
Why can’t enzymes that break down starch’s glycosidic bonds break down cellulose’s?
They cannot reach them, providing structural support
What are chitin’s properties and uses?
Strong, lightweight and waterproof.
Forms insect exoskeletons and is found in fungi cell walls.
What is chitin’s structure?
Similar to cellulose, but with some OH replaced by nitrogen containing acetylamine groups.
What are carbohydrates’ two main functions?
- energy source for plants and animals
- structural support for plants and insects.
Why are disaccharides known as ‘non-reducing sugars?’
They can’t reduxe the blue copper sulfate in the Benedict’s solution.
