Module 6

Question 1

What are the functions of proteins?

Answer 1

catalysis
defense
transport
structure
movement
signaling

Question 2

what are the different ways you can classify proteins

Answer 2

structure
composition
function

Question 3

what are the ways you can classify proteins based on structure

Answer 3

fibrous proteins
globular proteins

Question 4

what are the ways you can classify proteins based on composition

Answer 4

simple proteins
conjugates proteins

Question 5

what is the biuret test used for

Answer 5

check for the presence of peptide bonds, but can also be used to the concentration of proteins in an analyte

Question 6

what is the indication for a positive result in a biuret test

Answer 6

purple complex

Question 7

explain how the purple complex came to be

Answer 7

copper sulfate reacts with 2 or more peptide bonds, which gives a violet complex because cupric ions form a co-ordination complex with unshared electron pairs of peptide nitrogen and oxygen of water

Question 8

when should u use biuret test?

Answer 8

*detect presence of proteins in biological fluids
*detect amount of protein in urine

Question 9

can you detect protein quantitatively? how?

Answer 9

yes, by using spetrophotometric analysis

Question 10

reagents and test solutions biuret test

Answer 10

reagents:
10% sodium hydroxide
0.5% copper sulfate

test solutions:
5% albumin
5% arginine
5% glycine
distilled water

Question 11

what gives a positive and negative result of a biuret test

Answer 11

positive: purple/violet complex
negative: blue complex

Question 12

what gives a positive result for biuret test

Answer 12

all proteins and peptides, and histidine

Question 13

what amino acid gives a biuret a positive result

Answer 13

histidine

Question 14

since magnessium and ammonium ions interfere with the biuret test, what can overcome this interference?

Answer 14

excess alkali

Question 15

why shouldnt you use biuret test

Answer 15

high concentrations of ammonium salts and bile pigment can influence the results.

not as sensitive as the folin lowry test

Question 16

what is xanthoproteic test used for

Answer 16

detext amino acids that have phenolic or indolic groups

Question 17

what amino acids have phenolic and indolic groups

Answer 17

phenylalanine, tryptophan, and tyrosine

Question 18

how does the yellow complex appear in a xanthoproteic test

Answer 18

conc. nitric acid reacts with phenyl ring to give a yellow colored aromatic nitro compound.

addition of alkali(sodium hydroxide) will give deepen the color to orange

Question 19

what are reagents and test solutions of the xanthoproteic test

Answer 19

reagent:
nitric acid
40% sodium hydroxide

test solution
1% tyrosine
1% tryptophan
1% phenylalanine
5% egg white
distilled water

Question 20

why does phenylalanine give a positive in the xanthoproteic test

Answer 20

because it has a highly stable phenyl group

Question 21

when or why should you use the xanthoproteic test

Answer 21

to differentiate between aromatic and non-aromatic amino acids

Question 22

why shouldnt u use the xanthoproteic test

Answer 22

because even tho phenylalanine is an aromatic group group, it does not give a positive

Question 23

what is ninhydrin used for

Answer 23

detect ammonia, a-amino acids, primary/secondary amines

Question 24

how does the ruhemann pruple form in the ninhydrin test

Answer 24

when ninhydrin reagent is added to a test sample that has an amino group

Question 25

if proline or hydroxy proline were used in the ninhydrin test what would happen

Answer 25

it would make iminium salts, which will make yellow-orange product

Question 26

if free amino groups like asparagine were used in the ninhydrin test whaat would happen

Answer 26

it would produce a brown colored product

Question 27

reagents and test solutions of the ninhydrin test

Answer 27

reagent
2% ninhydrin solution