Biochemical Tests and Structures - Scholarly Flashcards
Front
Back
Outline the Benedict’s test for reducing sugars.
- Add an equal volume of Benedict’s reagent to the sample to be tested. 2. Heat the mixture in a water bath at 100°C for 5 minutes. 3. Positive result: colour change from blue to green to yellow to orange to brick-red. Precipitate forms.
Outline the Benedict’s test for non-reducing sugars.
- Conduct a reducing sugar test; if the result is negative the reagent remains blue. 2. Hydrolyse non-reducing sugars (e.g. sucrose) into their monomers by adding an equal volume of HCl. 3. Heat in a boiling water bath for 5 minutes. 4. Neutralise the mixture using sodium hydrogen carbonate solution. 5. Proceed with the Benedict’s test as usual.
How can the Benedict’s test be made more quantitative?
Either measure the time from immersing the solution in the water bath until the first colour change is produced or create standard solutions of known concentrations and compare colour change to estimate concentration.
Outline the Biuret test for proteins.
- Add an equal volume of sodium hydroxide to a sample at room temperature. 2. Add a few drops of dilute copper II sulfate solution. Swirl to mix. (Steps 1 and 2 make the Biuret reagent.) 3. Positive result: colour change from pale blue to purple. Negative result: solution remains blue.
Describe how to test for and measure the presence of starch in a sample.
- Add iodine solution. 2. Positive result: colour changes from yellow-brown to blue-black.
Describe the emulsion test for fats and oils.
- Add ethanol to the sample and shake. 2. Allow the mixture to settle. 3. Add an equal volume of water. 4. Record any observations.
Describe the positive result of an emulsion test.
White cloudy emulsion forms.
Define monomer.
A single subunit that is used to build larger polymers.
Define polymer.
A large molecule comprising of repeating subunits (monomers) often joined by condensation.
Define macromolecule.
A large biological molecule.
Define monosaccharide disaccharide polysaccharide.
- Monosaccharide: A single unit of carbohydrate. 2. Disaccharide: 2 units of carbohydrate joined by condensation held by a glycosidic bond. 3. Polysaccharide: A polymer with monomers of monosaccharides joined together by condensation held by glycosidic bonds.
Draw and describe the structure of α-glucose and β-glucose.
Both are hexose monosaccharides (6C) with a ring structure.
What is the difference between α-glucose and β-glucose?
The OH group on carbon 1 for α-glucose is below the plane while that for β-glucose is above the plane.
What happens in condensation reactions with reference to glycosidic bonds?
A chemical bond forms between two molecules and a molecule of water is produced. H is removed from one molecule and OH from another. When this occurs between carbohydrates it is referred to as a glycosidic bond which is a type of covalent bond.
What is meant by the terms reducing and non-reducing sugars?
Reducing sugar: is able to reduce other sugars to form di- or polysaccharides due to free groups which can be condensed. All monosaccharides are reducing sugars. Non-reducing sugars: do not possess a condensable free group and cannot reduce other sugars.
State whether the following are reducing or non-reducing sugars: glucose fructose maltose sucrose.
Reducing: Glucose Fructose Maltose. Non-reducing: Sucrose.
State how sucrose is formed via the formation of a glycosidic bond.
Glucose and fructose form sucrose via the omission of H2O in a condensation reaction forming a glycosidic bond between them.
How are glycosidic bonds broken? What is this known as?
Water is used to break the glycosidic bond. This is known as a hydrolysis reaction.
Describe the structures of amylose and amylopectin.
Amylose: 14-glycosidic bonds; unbranched helical structure. Amylopectin: 14 and 16-glycosidic bonds; branched structure.
How do the structures of amylose and amylopectin relate to their function?
Amylose and amylopectin act as storage polymers of α-glucose in plant cells. They are insoluble have no osmotic effect on cells and are large thus do not diffuse out of cells. Amylose is compact due to its unbranched helical structure. Amylopectin has many terminal ends for rapid hydrolysis into glucose.
Describe the structure and functions of glycogen.
Glycogen is the main storage polymer of α-glucose in animal cells (but also found in plant cells) and consists of 14 and 16-glycosidic bonds. It is more branched than amylopectin has many terminal ends for hydrolysis is insoluble has no osmotic effect does not diffuse out of cells and is compact.
Describe the structure and functions of cellulose.
Cellulose is a polymer of β-glucose polysaccharide that gives rigidity to plant cell walls preventing bursting under turgor pressure and holding the stem up. It has 14-glycosidic bonds and consists of a straight-chain unbranched molecule. Alternate glucose molecules are rotated 180 degrees and H-bond crosslinks between parallel strands form microfibrils giving it high tensile strength.
What is the difference between saturated and unsaturated fats?
Saturated fats have no C=C bonds and are solid at room temperature due to strong intermolecular forces. Unsaturated fats have one or more C=C bonds and are liquid at room temperature due to weak intermolecular forces.
