carbohydrates - disaccharides Flashcards
(19 cards)
describe the difference between alpha and beta glucose
in alpha glucose the OH group on carbon 1 points downwards whereas in beta glucose the OH group on carbon 1 points upwards
which 2 monomers make up sucrose
glucose + fructose
which 2 monomers make up maltose
glucose + glucose
which 2 monomers make up lactose
glucose + galactose
what is the function of sucrose
sucrose is a transport sugar and a storage form of energy in plants and is a product of photosynthesis which is transported in the phloem
describe the reaction that is involved in joining 2 monosaccharides
a condensation reaction joins 2 monosaccharides together by forming a chemical bond between the monosaccharides by removing a water molecule forming a glycosidic bond
what is the bond that links 2 glucose molecules together in maltose
1-4 glycosidic bond
describe how you would tests for the presence of a reducing sugar
the Benedict’s test - add an equal amount of Benedict’s and the solution being tested and heat it to at least 70 degrees. if a reducing sugar is present the solution will turn from blue to brick red
what colour change will be observed if a reducing sugar is present when testing for reducing sugar
the solution will turn from blue through green, yellow and orange and the a brick red precipitated will form
why does a colour change from blue to red happen when testing for reducing sugars
as these sugars donate a electron to reduce copper (III) ions in copper sulphate to red copper (I) oxide
why is testing for reducing sugars a semi-quantitative test
as it provides and estimate of the sugar concentration based on a colour change rather than a precise measurement
describe what you would do to test for a non reducing sugar
to tests for non reducing sugars you need to heat the solution being tested with hydrochloric acid and then carry out the benedicts test and if the solution then turn red then a non reducing sugar was present
what colour change will happen if a non reducing sugar was present
the solution will turn red if a non reducing sugar was initially present
when testing for a non reducing sugar why does it needed be heated with hydrochloric acid first
as Benedict’s needs alkaline conditions to work so an alkali is added
what is the general formula of a disaccharide
C12H22O11
Where is lactose found
in milk in mammals - its the main carbohydrate in milk
what is the function of maltose
has a role in germinating seeds
why is the bond formed between disaccharides called 1-4 glycosidic
as it between C1 and C4
