3.1.2 carbohydrates Flashcards
what is a monosaccharide?
+ the monomers from which larger carbohydrates are made
+ simple sweet-tasting sugar
general formula ( CH2O)n
+ n can be anywhere from 3-7
+ glucose, galactose and fructose are common
what happens in a condensation reaction between 2 monosaccharides?
+ a glycosidic bond is formed
how are disassachrides formed?
+ by the condensation of two monosaccharides
what is maltose?
+ a disaccharide formed by condensation of two glucose molecules
what is sucrose?
+ a disaccharide formed by condensation of a glucose molecule and a fructose molecule
what is lactose?
+ a disaccharide formed by condensation of a glusoce molecule and a galactose molecule
what are the two isomers of glucose?
+ alpha-glucose
+ beta-glucose
how are polysaccharides formed?
+ by the condensation of many glucose units
how is glycogen and starch formed?
+ by the condensation of alpha-glucose
how is cellulose formed?
+ by the condensation of beta-glucose
What are carbohydrates?
+ contains only C,H,O atoms
+ carbon atoms form bonds with each other allowing for long chains to be formed
+ can be used as a backbone for other atoms to join in order to form other molecules
+ in all organisms the function is it act as an easily accessible source of energy
+ in plants, carbs also have a structural role
Formula of a triose sugar?
C3H6O3
Formula of tetrose sugar?
C4H8O4
Formula of pentose sugar?
C5H10O5
Formula of hexose sugar?
C6H12O6
Formula of heptose sugar?
C7H14O7
What is an isomer?
+ same molecular formula but different structure (their atoms are arranged to give them slightly different properties)
What is the test for starch?
+ add iodine solution
+ blue/black precipitate forms if
What is a reducing sugar?
+ a sugar that can donate electrons (or hydrogen) to other chemicals
What is Benedict’s Reagent?
+ an alkaline copper (II) sulphate solution
How do you test for reducing sugars?
- Test tube with food sample dissolved in water
- Add an equal volume of Benedict’s Reagent
- Heat the mixture in gently boiling water
How are disaccharides formed?
+ two alpha-glucose molecules C1 and C4 meet
+ hydroxyl group (OH) from C1 and C4 react
+ a condensation reaction occurs so water is removed- so there will be less oxygen and hydrogen
+ the bond formed is caused an alpha-1,4 glycosidic linkage
How to test for non-reducing sugars?
- add liquid food sample to a test tube
- add 1cm^3 of hydrochloric acid (hydrolyses the disaccharide)
- place in a beaker of water and boil for approx. one minute
- allow the test tube to cool
- add sodium hydrogencarbonate to neutralize the acid
- carry out Benedict’s test as for reducing sugars
- non-reducing sugar present = brick red precipitate
what are polysaccharides?
+ formed by combinations of many monosaccharides molecules
+ they are joined by glycosidic bonds that were formed by condensation reactions (many bonds present within polysaccharides)
+ they are insoluble as they are large, making them highly suited for storage