5 Questions
Explain the principle behind the color change observed when iodine interacts with glycogen.
Iodine molecules fit into the helical structure of glycogen, causing a change in the absorption spectrum and leading to the observable color change.
How does the iodine test differentiate between starch and glycogen?
In the presence of iodine, starch forms a bluish-black coloration, while glycogen forms a reddish-brown color due to the formation of different complexes.
What is the significance of the gradient ethanol precipitation method in isolating polysaccharides?
The method allows for the step-by-step precipitation of polysaccharides like starch and glycogen, aiding in their extraction and isolation.
Explain why starch and glycogen exhibit limited solubility in most solvents.
Starch and glycogen have limited solubility due to their complex and helical structures, making them insoluble in many common solvents.
How does the concept of 'iodine molecule entrapment' apply to the colorimetric determination of starch and glycogen?
In complex carbohydrates like starch and glycogen, iodine molecules get entrapped within their helical chains, resulting in distinct color changes during testing.
Study Notes
Glycogen Extraction
- Oyster meat was homogenized using a mortar and mixed with water to extract glycogen.
- Proteins were precipitated by heating the mixture in a boiling water bath for 5 minutes, and then 1 mL of 0.1% acetic acid was added to enhance precipitation.
- The resulting mixture was filtered, yielding an extract enriched with glycogen.
Iodine Test
- Iodine is used to distinguish starch and glycogen from other polysaccharides.
- Starch produces a distinct blue-black color when mixed with iodine, while glycogen produces a deep red color.
- The iodine test is based on the principle of "iodine molecule entrapment" within the helical chains of complex carbohydrates.
- In starch, iodine molecules become entrapped within the helical chain of amylose, resulting in a bluish-black coloration.
- In glycogen, iodine molecules fit into the helical structure, causing a change in the absorption spectrum and leading to a color change.
Carbohydrate Precipitation
- The gradient ethanol precipitation method involves gradual addition of ethanol to a solution containing polysaccharides, leading to step-by-step precipitation.
- This method is commonly used to extract and isolate starch or glycogen from a mixture.
- Starch and glycogen exhibit limited solubility in most solvents.
- Glycogen and starch can be precipitated using ethanol, resulting in a positive test.
Hydrolysis
- Hydrolysis using strong acid (hydrochloric acid) can be used to estimate the polysaccharide content of a sample.
Test your knowledge on the processes involved in glycogen extraction and hydrolysis, including Fehling's test, Iodine reaction, and precipitation with alcohol and hydrochloric acid. Learn about the methods used to estimate polysaccharide content in a sample.
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