carbohydrates Flashcards
what elements do carbohydrates contain
- carbon
- hydrogen
- oxygen
what is the general formula for carbohydrates
Cx(H2O)y
monosaccharide examples
glucose
fructose
ribose
disaccharide examples
lactose
sucrose
maltose
polysaccharide examples
glycogen
cellulose
starch
what is a monosaccharide
a single sugar unit
formula of glucose
C6H12O6
hexose monosaccharide (6 carbons)
what is the difference between alpha and beta glucose
alpha glucose has its OH ion on carbon 1 below
beta glucose has its OH ion from carbon 1 above
characteristics of glucose
- polar
- soluble due to hydrogen bonds that form between the hydroxyl groups and the water molecules
- solubility means glucose is dissolved in the cytosol of the cell
condensation reaction between 2 alpha glucose
- 2 hydroxyl groups interact
- forms a water molecule
- carbon 1 and carbon 4 bond
- glycosidic bond made
- maltose is made (disaccharide)
what is sucrose made from
glucose and fructose
examples of hexose monosaccharides
glucose
fructose
galactose
what is the disaccharide lactose made from
glucose
galactose
pentose monosaccharides
- 5 carbon atoms
- ribose in RNA nucleotides
- deoxyribose in DNA nucleotides
what is starch made from
- many alpha glucose molecules joined by glycosidic bonds
- form 2 slightly different polysaccharides
what is amylose
one of the polysaccharides in starch
- formed by alpha glucose molecules joined by 1-4 glycosidic bonds
- angle of the bond means that this long chain of glucose twists to form a helix which is further stabilised by hydrogen bonding
-makes the polysaccharide more compact and less soluble than the glucose molecules used to make it
what is amylopectin
- one of the polysaccharides in starch
- made by 1-4 glycosidic bonds between alpha glucose molecules
- also some glycosidic bonds formed by condensation reactions between carbon 1 and 6 on 2 glucose molecules
- this means that amylopectin has a branched structure
(1-6 branching points every 25 subunits) - insoluble, compact
what is glycogen in relation to starch
the functionally equivalent molecule to starch in animals and fungi
structure of glycogen
- forms more branches than amylopectin
- so its more compact and less space is needed for it to be stored
- this is important as animals are mobile, unlike plants
- branching means there are many free ends where glucose can be added/removed which speeds up processes of storing/releasing glucose molecules required by the cell
how is cellulose made
- chain of beta glucose molecules
- beta glucose molecules can only bond if alternate subunits are turned upside down
- so that their hydroxyl groups can interact
- when a polysaccharide is formed from glucose this way, it is unable to coil or form branches
- so forms a straight chain molecule called cellulose
what are microfibrils and macrofibrils
- when cellulose molecules make hydrogen bonds with each other, they form microfibrils
- microfibrils join to form macrofibrils
- macrofibrils combine to produce fibres
- fibres are strong and insoluble (cell walls)
what are reducing sugars
all monosaccharides and some disaccharides
they can donate electrons or reduce another molecule or chemical
what is the test for reducing sugars
Benedict’s reagent
an alkaline solution of copper(II) sulfate
boil it for 5 minutes
positive test- colour change from blue to brick red
how to carry out the test for reducing sugars
- place sample in boiling tube
- add equal volume of Benedict’s
- heat mixture gently in boiling water bath for 5 minutes
- reducing sugars will react with copper ions
- results in addition of electrons to the blue Cu2+ ions
- reduces them to brick red Cu+ ions
- the more reducing sugar present, the more precipitate formed and the less blue ions left in solution
- so the colour seen is a mixture of brick red and blue
- this will depend on the concentration of the reducing sugar present
- so this test is qualitative
how to carry out the test for non-reducing sugars
- boil sample with dilute HCl
- warm the sample with Benedict’s solution
this is because the non reducing sugar has been hydrolysed to reducing sugars
(e.g. sucrose goes to fructose and glucose)
test for starch
iodine test
-a few drops of iodine dissolved in potassium iodide solution are mixed with sample
- solution changes from yellow/brown to purple/black
