GLYCOGEN

Summary

In this biochemistry laboratory activity, students learn to extract glycogen from shellfish. The process involves grinding, boiling, and filtering shellfish meat to obtain a glycogen solution. Various chemical tests are performed, including iodine reaction, ethyl alcohol precipitation, and hydrolysis followed by Felling’s test, to demonstrate glycogen’s properties. Students observe the color changes during the reactions, noting differences between unhydrolyzed and hydrolyzed glycogen. The activity concludes with students documenting their findings in a formal report, enhancing their understanding of polysaccharides like glycogen and their chemical behavior.

Takeaways

• 😀 Glycogen is a polysaccharide found in animal muscles and shellfish, which is the source for this experiment.
• 😀 The experiment begins with grinding the shellfish meat and adding sand to help break it down into a fine mixture.
• 😀 40 ml of water is added to the ground shellfish, and the mixture is boiled for 20 minutes to extract glycogen.
• 😀 After boiling, the mixture is filtered, and the residue is washed twice with 10 ml of water to collect the filtrate.
• 😀 The filtrate is then boiled to reduce its volume by half, concentrating the glycogen solution.
• 😀 Acetic acid is added to the concentrated solution, and it is filtered again to yield the final glycogen extract.
• 😀 The glycogen solution is tested with iodine solution, which gives a distinct color reaction to differentiate glycogen from starch.
• 😀 Ethyl alcohol is added to a portion of the glycogen solution, resulting in a white precipitate as a positive reaction for glycogen.
• 😀 The glycogen solution undergoes hydrolysis using hydrochloric acid and sodium hydroxide before being tested with Fehling's reagent.
• 😀 The hydrolyzed glycogen solution turns from yellow to red when reacted with Fehling’s reagent, indicating the presence of glucose units.
• 😀 Unhydrolyzed glycogen does not show a positive reaction with Fehling's reagent, which confirms the importance of hydrolysis in revealing glucose.

Q & A

What is the source of glycogen in this laboratory demonstration?

The source of glycogen in this experiment is the meat of shellfish.

Why is sand added to the shellfish meat before grinding?

Sand is added to help grind the shellfish meat into a finer consistency, making the extraction process more effective.

What is the purpose of boiling the ground shellfish meat with water?

Boiling the ground shellfish meat with water helps to extract the glycogen from the tissue, which is then collected in the filtrate.

Why is the glycogen solution filtered after boiling?

The glycogen solution is filtered to remove any solid residue, leaving behind the liquid containing the extracted glycogen.

How is the volume of the glycogen extract reduced during the experiment?

The glycogen extract is boiled down to reduce its volume by half, concentrating the solution.

What is the role of acetic acid in the preparation of the glycogen solution?

Acetic acid is added to the concentrated glycogen solution to help remove impurities before it is filtered again.

What does the iodine test indicate about the glycogen solution?

The iodine test is used to check for the presence of polysaccharides like glycogen and starch. A color change indicates a positive result for these compounds.

What happens when ethyl alcohol is added to the glycogen solution?

When ethyl alcohol is added, a white precipitate forms, confirming the presence of glycogen.

What is the purpose of hydrolyzing the glycogen solution before the Failing’s test?

Hydrolyzing the glycogen solution breaks it down into glucose, which can then react with Failing’s reagent to produce a positive result for glucose.

How can you tell if the glycogen has been successfully hydrolyzed in the experiment?

Successful hydrolysis is indicated by the formation of a deep yellow color after adding Failing’s reagent, which indicates the presence of glucose.