2. Biological Molecules Flashcards
Describe the Benedict’s test for reducing sugars
-add equal volume of Benedict reagent to the sample to be tested.
-heat the mixture in a water bath at 100 degrees for 5 minutes
Positive result- blue to a green to yellow to orange to brick red
Describe the iodine test for starch
-add a few drops of iodine to the sample
-if starch is present, iodide ions in the solution interact with the Centre of starch molecules, producing with a distinctive blue-black colour
Describe the Benedict test for non-reducing sugars
- hydrolyse non reducing sugars into their monomers by adding an equal volume of HCl
- Heat in a boiling water bath for 5min
- Neutralize the mixture using sodium hydrogen carbonate solution
- Proceed with the Benedict’s test as usual.
Describe the emulsion test for lipids.
-add ethanol to the sample to be tested, shake to mix then add the mixture to a test tube of water
-if lipids are present, a milky emulsion will form
-if no lipid is present, the solution remains clear.
Describe the biuret test for proteins.
-a liquid solution of sample is treated with sodium or potassium hydroxide to make the solution alkaline.
-a few drops of copper(II) sulfate is added to the sample
-if protein is present, a color change from blue to lilac/purple will be observed
Describe a semi-quantitative Benedict’s test on a reducing sugar solution.
-can be carried out by setting up standard solutions with known concentrations of reducing sugar
-using serial dilution.
-each solution is then treated in the same way; add the same volume of Benedict’s solution to each sample and heat in a water bath that has been boiled.
-any color change observed for each solution of a known concentration of reducing sugars is then compared to the stock solution colors.
Define the term monomer
A single subunit that is used to build large polymers
Define the term polymer
A large molecule comprised of repeating subunits
Macromolecule
A large biological molecule
Eg: polysaccharides
Proteins (polypeptides)
Nuclei acids (polynucleotides)
What is the difference between alpha and beta glucose?
The OH group on carbon 1 for alpha glucose is below the ring, while that for the beta glucose is above the ring.
Define a monosaccharide
A single sugar monomer, all of which are reducing sugars
What is a disaccharide
A sugar formed from two monosaccharides joined by a glycosidic bond in a condensation reaction
What is a polysaccharide
A polymer formed by many monosaccharides joined by a glycosidic bond in a condensation reaction
Why are triglycerides energy reserves ?
Because they store more energy per gram due to their hydrocarbon chains.
What is a condensation reaction?
A chemical reaction involving the joining together of two molecules by removal of a water molecule
What is a hydrolysis reaction?
A chemical reaction in which a chemical bond is broken by the addition of a water molecule; commonly used to break down complex molecules into simpler molecules.
Equation for sucrose
Glucose+fructose
Equation for maltose
Glucose+ glucose
Equation for lactose
Glucose+galactose
Functions of triglycerides
- They make excellent energy stored because they are richer in carbon-hydrogen bonds than carbohydrates
- They act as an insulator against loss of heat just below the skin
- Metabolic source of water- when triglycerides are oxidized in respiration, they are converted to carbon dioxide and water.
What is the primary structure in a protein?
The sequence of amino acids in a polypeptide or protein.
What is a secondary structure in proteins?
The structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids (an ą-helix or B-pleated sheet)
What is the tertiary structure of a protein?
The compact structure of a protein resulting from the three-dimensional coiling of the chain of amino acids.
What is the quaternary structure of a protein?
The three-dimensional arrangement of two or more polypeptides, or of a polypeptide and a non-protein component such as haem, in a protein molecule.