carbohydrates Flashcards
what is the empirical formula for carbohydrates
CH2O(n)
what are monosaccharides
monomers from which different carbohydrates are made
give three examples of monosaccharides
glucose, fructose, gelactose
roles of monosaccharides
- used in respiration to release energy (ATP)
- monomers to form polymers
- building DNA/RNA
- chemical intermediate
why can glucose hydrogen bond to water
it is polar and soluble
what are disaccharides
two monosaccharide units liked together with covalent bonds
are disaccharides polymers
no
why are disaccharides not polymers
they are soluble and dont contain ‘many’ repeating units
give three examples of disaccharides
maltose, sucrose, lactose
how are disaccharides formed
by the condensation of two monosaccharides
what monosaccharides form maltose
alpha glucose + alpha glucose
what monosaccharides form sucrose
alpha glucose + fructose
what monosaccharides form lactose
alpha glucose + galactose
what bond forms disaccharides
glycosidic bonds
describe how maltose is formed
a condensation reaction occurs between two molecules of alpha glucose, during this process water is released and a glycosidic bond forms between C1 from one glucose and C4 from the other
maltose, sucrose and lactose: which is not a reducing sugar
sucrose (comes from plants)
why is the benedict’s test a semi-quantitative test
as there are a range of positive results, they have no unit but you can make comparisons between them
what forms benedicts solution
copper sulfate and dilute sodium hydroxide
why does benedicts solution contain the alkali dilute sodium hydroxide
the solution only works in alkaline solutions
what occurs in a positive result in benedicts test
reducing sugars donate an electron to the Cu2+ to form Cu+ ( the ion is being reduced)
what does a higher concentration of reducing sugars do to the benedicts solution
more copper (II) is reduced, so a greater volume of precipitate is formed, the colour turning orange or brick red
how do you make the benedict’s test fully quantitative
you can use a colourimeter or filter out the precipitate formed and measure its mass
reducing sugars equation
Cu2+ (aq) -> Cu+ (ppt)
e-
How to test for non-reducing sugars
- boil the solution you are testing in hydrochloric acid - hydrolysis will occur and it will release monosaccharides
- neutralise with alkali (eg. hydrogen carbonate)
- repeat benedicts test
- if goes ‘brick red’ then there was a reducing sugar
what sugar type are all monosaccharides
reducing
Cu2+ soluble or insoluble
soluble
Cu+ soluble or insoluble
insoluble (produces a precipitate)
name three polysaccharides
starch, glycogen, cellulose
how is starch formed
condensation reaction forms many glycosidic bonds between the C1 and C4 of many alpha glucose monomers. water is eliminated in this process.
how is amylose formed
extensive hydrogen bonds between monomers pull the starch polymer chain to a compact coil. this is amylose.
amylose: soluble or insoluble
insoluble
role of starch
store energy
features of starch (3)
-consists mainly of polysaccharide amylose-
- compact, so lots of energy can be stored in a small place
- insoluble, so wont diffuse out of cells
- insoluble, does not effect water potential of the cell
how is starch used as an ‘energy store’
hydrolysis of starch releases glucose, this is used in respiration to release energy in the form of ATP
what solution tests for starch
potasium iodide solution
chemical equation, testing for starch
I2 + K+ + I- -> I3-
where can cellulose be found
walls of plant cells
describe the formation of cellulose
a condensation reaction occurs between many beta-glucose monomers, forming man glycosidic bonds between the C1 and C4 of each monomer. every second alpha glucose is rotated 180 degrees, long straight chains are formed and water is eliminated
how are microfibrils formed
extensive hydrogen bonding between parallel cellulose strands
how are cellulose fibres formed
microfibrils are layered to form a larger macrofibril, macrofibrils are then layered to form cellulose fibres
properties of cellulose
fibrous, strong, tensile
what is the role of cellulose
- support plant cell walls
- protects bursting by osmosis (prevents osmotic lysis- cell bursting)
describe how to test for reducing sugars
mix solution with 2cm^3 of benedicts solution, heat in a water bath at 90degrees for 5 minutes. positive result will end in a colour change from light blue- green/orange/brick red
what is the difference between alpha glucose and beta glucose
alpha glucose- on c1 and c4 hydroxide below the plane of the ring on both carbons
beta glucose- hydroxide above the place of the ring on C1
name the similarities between starch and glycogen (5)
- both polymers made from alpha-glucose
- both compact
- both insoluble
- stores of energy for respiration
- condensation reaction between monomers form glycosidic bonds
how is amylose different to glycogen
- forms C1-C4 glycosidic bonds only
- found in plants
- forms unbranched, coiled chains
how is glycogen different to amylose
- forms C1-C4 glycosidic bonds and C1-C6 branches
- found in animals
- heavily branched
- more ‘terminal ends’- more rapid hydrolysis of glucose
