- Most carbohydrates are polymers
- Contain elements Carbon, Hydrogen and Oxygen
- Carbohydrates are made from Monosaccharides:
Formula for Glucose, Galactose and Fructose --- C6H12O6
- Glucose is a hexose sugar (6-Carbon) - this goes onto make larger chains such as Cellulose and Starch
- Alpha and beta forms of Glucose
You need to know a-glucose:
This is an alpha-glucose structure:
Two monosaccharides join together to form a disaccharide.
- Glucose + Fructose --> Sucrose
(sucrose is just regular table sugar) + hydrolysed down again by Sucrase
- Glucose + Galactose ---> Lactose
(lactose is the sugar in Milk - you can be intolerant to it) + hydrolysed by Lactase
- Glucose + Glucose --> Maltose
(Maltose is a product of starch digestion, broken down by the enzyme amylase)
+ hydrolysed to its monosaccharides again by maltase
- You are lactose intolerant if you don't make enough of the enzyme Lactase
- Lactase hydrolyses Lactose into its monosaccharides - glucose and galactose
- Undigested lactose is fermented by bacteria in the large intestine and can go onto cause intestinal complaints such as...
- Stomach cramps
- Excessive flatuence due to large volume of gas
... And obviously these are really unpleasant! So, before lactose-intolerant people drink milk, you can add lactase to it to pre-digest it for you.
- Lactose intolerance is bad for babies because their source of food is milk, so they need special Formula milk to be made for them.
Benedict's Test for Reducing Sugars
Test for reducing sugars: Reducing sugars = monosaccharides & some dissaccharides such as Maltose.
- You add Benedict's Reagent - Copper (II) sulfate which is blue
- You heat the sample
- If the sample contains reducing sugars such as glucose, galactose, fructose or maltose then the solution should turn brick red. (a red precipitate forms)
Test for non-reducing sugars:
- You boil the solution in dilute HCL (Hydrochloric Acid) and then neutralise with sodium hydrogencarbonate.
- You then do the Benedict's Test for the reducing sugars which would now have been hydrolysed into their constituent monosaccharides
- Then the same result- but compared with another sample of the same with just the reducing sugar test one on its own - so you can prove that it is non-reducing sugars.
Starch is made up of a mixture of two polysaccharide types - amylose and amylopectin
- Both are long chains of alpha-glucose
- Linked by glycosidic bonds
- Formed in condensation reactions
Starch-> Salivary Amylase and Pancreatic Amylase break it down into maltose
Maltase (from the intestinal epithelium) then breaks down maltose into alpha-glucose molecules
The test for Starch uses iodine dissolved in potassium iodide solution.
When starch is present:
Brown-orange changes to Blue-Black colour.