LCQ4

What is the disaccharide composition?

Two monosaccharides, sharing same molecular formula when composed of simple monosaccharide residues (lose an H2O when joining

Qualitative test

Indicate whether/not a substance is present

Quantitative test

allows you to determine how much of a substance is present

What is the negative control when testing for each of these macromolecules?

dH2O

What is a negative control meant to show?

Verifies how test result appears in absence of particular molecule which test is designed to identify

What is a positive control?

A test on a substance expected to give a positive reaction

Why use a positive control?

Shows how a positive result appears,

but also indicates something has gone wrong if positive control does not display expected results

What test is used to indicate the presence of lipids?

Sudan Test

What test is used to indicate the presence of proteins?

Biuret test

It takes 5 drops of a 0.50% ascorbic acid solution to decolorize 10 ml of DCPIP. It takes 10 drops of lemon juice to decolorize the same amount of DCPIP. What is the ascorbic acid content of the lemon juice?

0.25%

How to determine if disaccharide is present in any of the samples to be tested?

• Lugol’s test + Benedicts (some cases)

• Disaccharides can be hydrolyzed → monosaccharides by acid hydrolysis (HCl), then tested with Benedict’s

Benedict’s test is…

quantitative, measure of monosaccharide quantity

Lugol’s test for absence/presence of amylose/starch

a/p of glycogen

& cellulose-paper

What kind of test is it?

qualitative

Sudan’s test is…

qualitative

presence/absence of lipids

Biuret’s test is…

qualitative for proteins

Step 1 of DS identifying

Run Benedicts + Lugols, if both are negative perform acid hydrolysis (HCl + Heat)

Step (2) of DS

Neutralize, repeat Benedict’s then lugols,

Step (3) of DS

If Benedict’s is (+) post hydrolysis, while Lugols remains (-)

Disaccharide present → that was hydrolyzed to monosaccharides

Negative control: distilled water. What is the rationale?

shows the appearance of a true negative (ensures reagents aren’t contaminated).

Positive controls: known solutions: glucose (monosaccharide, reducing), sucrose (disaccharide, non-reducing), maltose or lactose (reducing disaccharides), starch or glycogen (polysaccharide).

What is the rationale?

demonstrates the expected positive colors for each reagent and confirms reagents/technique are working.