tests for biological molecules

Question 1

what does qualitative results refer to with biochemical tests

Answer 1

is the substance present or absent

Question 2

what does semi qualitative refer to

Answer 2

how much is present

Question 3

what are some reducing sugars

Answer 3

all monosaccharides plusmaltose and lactose
galactose
glucose
fructose
maltose

Question 4

what are some non reducing sugars

Answer 4

sucrose which is the only one i need to know. it is a disaccharide

Question 5

what is the method for the benedicts rest for reducing sugars

Answer 5

add a fixed volume (2cm3) to the sample into a test tube.
add equal amount of benedicts reagent
boil for 5 mins in a water bath

Question 6

what are the results for the benedicts test for reducing sugars

Answer 6

negative: the solution will remain blue

positive: will turn from blue to green then yellow, brown, brick red , red depending on the concentration

Question 7

what is the principal of the benedicts test for reducing sugars

Answer 7

when they are heated in the presence of an alkali they get converted to enediols.

the copper 2 ions are reduced to copper 1 ions which causes the colour change

Question 8

method for the modified benedicts test for non reducing sugars

Answer 8

add equal amount of HCL and heat for 3 mins to hydrolyse the glycosidic bond

add sodium hydrogen carbonate powder to neutralise

then the last step same as the other

Question 9

what test is used for proteins

Answer 9

the biuret test

Question 10

what are the results of the biuret test

Answer 10

negative- remains blue

positive- changes from blue to purple

Question 11

what is a negative control for the biuret test

Answer 11

to use water at the same volume as the sample

Question 12

what would be a positive control for the biuret test

Answer 12

use albumein which is the white protein in egg whites

Question 13

if a sample is solid what should you always do to make it easier to test

Answer 13

grind it up and add water

or melt if it is a lipid

Question 14

what is the method of the biuret test

Answer 14

add buiret reagent in a 5:1 ratio to the sample, mix and leave

Question 15

what is the method and the results for the translution mark test for lipids

Answer 15

put a drop of the sample onto some cloth and let it dry. if it is still transulcent after then it is a lipid. if it is opaque then it isnt

Question 16

what is the method for the emulsion test

Answer 16

mix the sample with equal volumes of ethanol and water, shake vigourously

The first step is to add 2cm3 of the fish to a dry and grease-free test tube. Next, add 5cm3 of alcohol to the sample and shake the test tube. Finally, add 5cm3 water to the sample and shake the test tube.

Question 17

what are the results for the emulsion test

Answer 17

negative- no emulsion will form

positive- a cloudy/milky white emulsion will form

Question 18

what is a positive control for the emulsion test

Answer 18

use a known oil

Question 19

what is a negative control for the emulsion test

Answer 19

use water

Question 20

what is the method for the iodine test

Answer 20

use iodine dissolved in potassium iodide,
add and mix

Question 21

what are the results for the iodine test

Answer 21

negative- stays yellow/brown

positive- turns from yellow/brown to blue/black

Question 22

what is the iodine test for

Answer 22

starch

Question 23

how can you test for water

Answer 23

water has a fixed melting and boiling point

Question 24

testing for the presence of oil in the fish was observed under an optical microscope. There were many lipid droplets visible. Explain why.

Answer 24

The non-polar regions of lipids are hydrophobic and they form micelles when added to water. When the mixture is shaken, the micelles are broken into even smaller micelles and distributed through the water. The lipid droplets visible are the micelles distributed throughout the test tube.

Question 25

An emulsion test is an example of a…

Answer 25

qualitative test because it tells you if the lipid is present or not in a sample.