5 Questions
Add 3 ml of Barfoed's reagent (a solution of cupric acetate and acetic acid).Heat the solution in a boiling water bath for 6 minutes(after the 3 min check the tubes).Tube glucose lactose starch observation 4.Bial’s Test: Objective: To distinguish between pentose monosaccharide and hexose monosaccharide Principle: Bial’s test uses concentrated HCl as a dehydrating acid and orcinol + traces of ferric chloride [FeCl3] as condensation reagent.The test reagent dehydrates pentoses to form furfural.Furfural further reacts with orcinol and the iron ion present in the test reagent to produce a bluish or green product, while hexoses yield muddy-brown to grey condensation product.Method : Put 2 ml of a sample solution in a test tube.Add 3 ml of Bial's reagent (a solution of orcinol, HCl and ferric chloride) to each tube.Heat the tubes gently in hot water bath.If the color is not obvious, more water can be added to the tube.Tube 1-glucose 2-ribose observation 5.Seliwanoff's Test: Objective: used to distinguish between aldoses (like glucose) and ketoses (like fructose).Principle: Seliwanoff's Test uses 6M HCl as dehydrating agent and resoncinol as condensation reagent.The test reagent dehydrates ketohexoses to form 5-hydroxymethylfurfural. 5hydroxymethylfurfural further condenses with resorcinol present in the test reagent to produce a cherry red product within two minutes.-Aldohexoses react to form the same product, but do so more slowly giving yellow to faint pink color.
Can we use ______ method in fractionating mixture of proteins?
salting out
What is the least number of amino acids bonded together by peptide bonds that will respond positively to biuret test?
two
After heating albumin at high temperature, does it still biologically active? Why?
No, denaturation
Do you think free amino acids will give a positive result with biuret test? Why?
No, need peptide bonds
Study Notes
Carbohydrates
- Carbohydrates are the primary source of energy for living things and serve as extracellular structural elements in bacterial and plant cell walls.
- Carbohydrates are defined as polyhydroxy aldehydes or polyhydroxy ketones, and most have the formula (CH2O)n.
- In the human body, D-glucose is used, and simple sugars end with the suffix –ose.
Classification of Carbohydrates
- Carbohydrates can be classified as:
- Simple sugars (monosaccharides): one monosaccharide unit
- Complex sugars:
- Disaccharides: two monosaccharide units
- Oligosaccharides: 3-9 monosaccharide units
- Polysaccharides: more than 9 monosaccharide units
Chemical Properties of Carbohydrates
- Carbohydrates can undergo hydrolysis to break down into smaller sugar units.
- Reducing and non-reducing sugars:
- Reducing sugars: can act as a reducing agent and are termed reducing sugars
- Non-reducing sugars: cannot act as a reducing agent
- Solubility of sugars:
- Monosaccharides and disaccharides can be dissolved freely in water
- Polysaccharides cannot be dissolved easily in water due to their high molecular weight
Qualitative Tests for Carbohydrates
- Molisch Test:
- Specific for all carbohydrates
- Monosaccharides give a rapid positive test, while disaccharides and polysaccharides react slower
- Benedict's Test:
- Objective: to detect the presence of reducing sugars
- Reducing sugars are oxidized by copper ions in solution to form a carboxylic acid and a reddish precipitate of copper(I) oxide
- Barfoed's Test:
- Objective: to distinguish between mono-, di-, and polysaccharides
- Reducing monosaccharides are oxidized by copper ions in solution to form a carboxylic acid and a reddish precipitate of copper(I) oxide
- Bial's Test:
- Objective: to distinguish between pentose monosaccharides and hexose monosaccharides
- Dehydrates pentoses to form furfural, which reacts with orcinol and ferric chloride to produce a bluish or green product
- Seliwanoff's Test:
- Objective: to distinguish between aldoses and ketoses
- Dehydrates ketohexoses to form 5-hydroxymethylfurfural, which condenses with resorcinol to produce a cherry red product
Qualitative Tests for Proteins
- Biuret Test:
- Objective: to detect the presence of peptides or proteins in a sample
- Principle: Proteins and peptides react with an alkaline solution of dilute copper sulfate to form a violet color
- Effects of Salt Concentration on Protein Solubility:
- Low salt concentration solutions make protein solubility easier (salting in)
- High salt concentration solutions cause protein to precipitate (salting out)
- Precipitation of Proteins by Acids:
- Objective: to investigate the effects of strong acids on protein solubility
- Principle: In highly acidic media, proteins will be positively charged and attract acid anions, causing them to precipitate
- Precipitation of Proteins by Salts of Heavy Metals:
- Objective: to identify the effect of heavy metal salts on protein
- Principle: Heavy metal salts disrupt salt bridges in proteins, leading to an insoluble metal protein salt
- Protein Denaturation:
- Objective: to investigate the effect of high temperature on protein structure
- Principle: Non-covalent bonds can be broken by heating, leading to protein denaturation and precipitation
Test your knowledge on the qualitative tests used for carbohydrates, the key source of energy for living things. Learn about their structural elements, classifications, and importance in the human body.
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