Biological structures Flashcards
Tests for reducing sugars
Benedict’s test for reducing sugars
Benedict’s test for reducing sugars
A food sample is dissolved in boiling water. Next, a small amount of Benedict’s reagent is added and the solution begins to cool. During the next four to 10 minutes, the solution should begin to change colors. If the color changes to blue, then no glucose is present.
Tests for non-reducing sugars
Benedict’s test for non-reducing sugars.
Benedict’s solution for non-reducing sugars
If a reducing sugar is present in a solution, adding Benedict’s reagent and heating will form an insoluble red precipitate. Non-reducing sugars do not change the colour of the solution, which is blue, and so we have to break the sugar down to monosaccharides by hydrolysis to prove they’re non-reducing.
Test for starch
Iodine-starch test.
Iodine-starch test
In the presence of starch, iodine turns a blue/black colour. For example, if iodine is added to a peeled potato then it will turn black. Benedict’s reagent can be used to test for glucose.
Test for lipids
Emulsion test.
Emulsion test
The procedure is for the sample to be suspended in ethanol, allowing lipids present to dissolve (lipids are soluble in alcohols). The liquid (alcohol with dissolved fat) is then decanted into water.
Test for proteins
Biuret test.
Biuret test
Add an equal volume of potassium hydroxide solution to the tube and stir.
Add two drops of copper sulfate solution and stir for two minutes.
Record the colour of the solution.
If the solution is purple, then it has proteins.
What is a monomer?
A single molecule that can be bonded to other identical molecules to form a polymer.
What is a polymer?
A polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits.
What is a macromolecule?
A molecule containing a very large number of atoms, such as a protein, nucleic acid, or synthetic polymer.
What is a monosaccharide?
Any of the class of sugars that cannot be hydrolysed to give a simpler sugar. Eg. glucose.
What is a disaccharide?
Any of a class of sugars whose molecules contain two monosaccharide residues.
What is a polysaccharide?
A carbohydrate whose molecules consist of a number of sugar molecules bonded together. Eg. starch.
Formation of a glycosidic bond by condensation
Condensation occurs wherein hydroxyl groups in the ring structures of the monosaccharides align next to each other, and a water molecule is created (i.e., 2 hydrogens and 1 oxygen are lost from the ring structure).
The oxygen that is left forms a bridge with between the two monosaccharides - also known as a glycosidic bond.
Breakage of glycosidic bonds in polysaccharides and disaccharides by hydrolysis
Breakage is when water is added back to the ring structure.
As such, this process is the opposite of condensation, and is called ‘hydrolysis’
Here, disaccharides and polysaccharides breakdown into monosaccharides.
Hydrochloric acid can be used to break disaccharides down into two monosaccharides when testing for the presence of non-reducing sugars (e.g., sucrose).
Molecular structure of polysaccharides
These are complex carbohydrates made up of repeating units of monosaccharides that are attached together by Glucosidic linkage. A molecule of a polysaccharide has n number of sugar molecules bound together to form a larger molecule.
Function of starch
Store energy for plants.
Function of glycogen
Store energy for animals.
Function of cellulose
Helps plants to remain stiff and upright.
Molecular structure of a triglyceride and function
Triglycerides are the main energy storage molecules of plants and animals. Triglycerides are made of a glycerol molecule bonded to three fatty acid chains.
Structure of a phospholipid and functions
Phospholipids consist of a hydrophilic head and a hydrophobic tail. Phospholipids like to line up and arrange themselves into two parallel layers, called a phospholipid bilayer. This layer makes up your cell membranes and is critical to a cell’s ability to function.
