T1: Carbohydrates and Food tests Flashcards
what is a carbohydrate?
made from C,H,O
many monosaccharides joined together
common monosaccharides
glucose, galactose, fructose
what makes maltose?
glucose and glucose
what makes lactose?
glucose and galactose
what makes sucrose?
glucose and fructose
common disaccharides
maltose, lactose, sucrose
formed by the condensation of 2 monosaccharides forming a glycosidic bond
define polysaccharide
polymer formed by the condensation of more than two monosaccharides
e:g starch,glycogen and cellulose
polysaccharide(s) of alpha glucose
starch and glycogen
polysaccharide of beta glucose
cellulose
two isomers of glucose are…
alpha glucose + beta glucose
ABBA
alpha has OH below
beta has OH above
how to draw glucose
hexagonal shape with overlapping lines
H then HO on left
O in top right of hexagon
what is starch made from?
two polysaccharides of alpha glucose
amylose + amylopectin
describe amylose
long unbranched chain with alpha 1,4 glycosidic bonds
the angles of the glycosidic bonds give it a coiled structure SO its compact for energy storage
describe amylopectin
branched chain of alpha glucose with many side branches
has both alpha 1,4 AND 1,6 glycosidic bonds
side branches allow enzymes to hydrolyse the glycosidic bonds easily SO glucose can be released quickly
starch structure and function
large insoluble molecule SO osmotically inactive
large molecule SO cant cross the cell surface membrane and leave the cell
coiled AND branched SO compact for energy storage
branched SO glucose is easily hydrolysed for respiration
describe glycogen
many branches but NOT coiled
has more branches than amylopectin
many branches so fast release of glucose + compact
describe cellulose
long unbranched chains of beta glucose linked by hydrogen bonds to form microfibrils
cellulose structure and function
long straight chains of beta glucose FORM strong microfibrils (provide support for cells)
hydrogen bonding between chains provides rigidity and strength
what does cellulose do in plant cell walls?
prevents them from bursting when water enters by osmosis
what are the colour changes for Benedicts test for sugars?
blue
green
yellow
orange
brick red
traffic lights + blue n yelllow
what are the reducing sugars?
galactose
fructose
maltose
glucose
describe Benedicts test for reducing sugars
add Benedicts reagent to sample
heat in a boiling water bath for 5 minutes
if +ve colored ppt forms
what are the non reducing sugar(s)?
sucrose
describe Benedicts test for non reducing sugars
get new sample + add HCl
heat in a boiling water bath for 5 minutes
neutralise by adding alkali
add Benedicts reagent and heat again
if +ve colored ppt forms
if stays blue no sugars are present
describe the starch test
add a few drops of iodine in KI
if +ve then orange to blue/black
describe the Biuret test for proteins
add a few drops of NaOH (makes sol alkaline)
add some copper (II) sulfate solution
if +ve blue to lilac
describe the lipid test
grind food sample
add ethanol AND shake
add mix to water
if +ve a milky emulsion forms
