section 1: biological molecules Flashcards
1
Q
test for reducing sugars
A
- all monosaccharides and some disaccharides are reducing sugars
- add 2cm of the food sample to be tested in a test tube
- add an equal volume of Benedict’s reagent
- heat the mixture in a water bath for 5 minutes
- if reducing sugar is present there will be a colour change to red/brown
- different colours can show different amounts of reducing sugar : blue = none, green = very low, yellow = low, orange = medium, red = high
2
Q
test for non-reducing sugars
A
- add 2cm of the food sample being tested to 2cm of Benedict’s reagent in a test tube and filter
- put test tube in water bath for 5 minutes, if no colour change then reducing sugar is not present
- add another 2cm of the food sample to 2cm of dilute hydrochloric acid in a test tube and place in water bath for 5 minutes, the hydrochloric acid will hydrolyse any disaccharide present into its monosaccharides
- slowly add some sodium hydrogencarbonate solution to the test tube to neutralise the acid
- re test the solution by heating it with 2cm of Benedict’s reagent in a water bath for 5 minutes
- if a non-reducing sugar was present in the original sample then the Benedict’s solution will now turn orange/brown due to reducing sugars that have been produced
3
Q
test for starch
A
- place 2cm of sample being tested into a test tube
- add two drops of iodine solution and shake
- if starch is present there will be a colour change to blue/black
4
Q
what does saturated mean ?
A
no double bonds between carbon atoms
5
Q
what does unsaturated mean?
A
there is double bond between carbon atoms
6
Q
test for lipids
A
- known as the emulsion test
- take a completely dry and grease free test tube and add 2cm of the sample being tested
- add 5cm of ethanol
- shake thoroughly to dissolve any lipid in the sample
- add 5cm of water and shake gently
- a cloudy-white colour indicates the presence of a lipid
7
Q
test for proteins
A
- the Biuret test which detects peptide bonds
- put a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature
- add a few drops of very dilute copper sulfate solution and mix gently
- a colour change to purple indicates peptide bonds are present, if it remains blue there are none
8
Q
what bond is between 2 monosaccharides
A
glycosidic bonds
9
Q
monomers
A
are the smaller repeating units from which larger molecules are made to by joining them to make polymers
10
Q
polymers
A
a molecule made from a large number of monomers joined together
11
Q
condensation reaction
A
removing water from something to make new bonds
12
Q
hydrolysis reaction
A
adding water to something to break it’s bonds
13
Q
monosaccharides
A
- glucose
- galactose
- fructose
14
Q
disaccharides
A
- maltose (glucose + glucose)
- sucrose (glucose + fructose)
- lactose (glucose + galactose)
15
Q
polysaccharides
A
- starch
- glycogen
- cellulose