Topic: Proteins – properties

Target group

Elementary school student (grades 7. and 8.)

Core curriculum

Elementary school. Chemistry.

X. Chemical substances of biological importance. Student:

6) investigates protein behavior under the influence of heating, ethanol, acids and bases, heavy metal salts (e.g. CuSOIndeks dolny 4₄) and sodium chloride; describes differences in the course of denaturation and coagulation of proteins; lists the factors that trigger these processes; designs and conducts experiments to detect the presence of protein with a concentrated solution of nitric acid in various food products;

General aim of education

The student acquires knowledge and skills about the topics discussed in the classes

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• define the concepts: denaturation and shedding of protein;

• exchange factors that cause denaturation and protein shedding;

• indicate the difference between denaturation and protein shedding;

• design an experiment to detect the presence of protein in food products and taking into account factors that cause denaturation and protein shedding.

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• exposing

  • film.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers.

Lesson plan overview

Introduction

1. The teacher hands out Methodology Guide or green, yellow and red sheets of paper to the students to be used during the work based on a traffic light technique. He presents the aims of the lesson in the student's language on a multimedia presentation and discusses the criteria of success (aims of the lesson and success criteria can be send to students via e‑mail or posted on Facebook, so that students will be able to manage their portfolio).

2. The teacher together with the students determines the topic – based on the previously presented lesson aims – and then writes it on the interactive whiteboard/blackboard. Students write the topic in the notebook.

Realization

1. The teacher introduces students to the issue of protein properties. He asks them to give examples of molecual and colloidal dispersions (here the example of egg white with water should be mentioned). He or she asks how to distinguish, for example, a solution of water and salt from a solution of water with egg white, which look identical..

2. The teacher forms six groups of students so that each experiment is carried out with one factor per protein (temperature - heating, ethanol, acid e.g. hydrochloric acid, base e.g. sodium base, heavy metal salts e.g. CuSOIndeks dolny 4₄ solution, sodium chloride). He or she recommends students to look into the abstract and asks them to read the instructions of Experiments 1 and 2 (according to the division into groups).The teacher distributes work cards, in which students will write their observations and conclusions. When the students become familiar with the instructions, the teacher instructs them to formulate the research problem (questions) and write it down in the work sheet. The groups perform the experiment, observe its course. Leaders note observations and conclusions on A4 pages, other students in work cards or in an abstract form. The teacher asks each leader to attach an A4 sheet of paper to the wall and present the effects of the group's work. Then he or she summarizes the experiment, referring to the conclusions and explaining what to do in case of drinking a heavy metal salt solution (poisoning)..

3. After the first experiment is finished, the teacher asks students from the group who conducted an experiment with sodium chloride and egg white, to add water to the tube, mixing its contents and present observations. Then the teacher explains the concept of reversible coagulation (salting out) - he or she gives some examples of „from the kitchen” sol and gel and explains what the difference between them is..

4. The teacher introduces students to the issues of detecting peptide bonds in egg white and detecting proteins in various food products. Displays a video from the „Detection of peptide bonds” abstract. After the broadcast, he summarizes the knowledge and presents another film material - „Detecting the presence of protein in food products”. The teacher stops the film immediately after the reaction of egg white to nitric acid and asks students what they observed. Then the class leader divides the students into groups that will detect the protein in the indicated food products (each group of other products). Students are to write observations and conclusions in their work sheets or forms in an abstract, and group leaders present them in the class. After the presentation, the teacher plays the film „Detecting the presence of protein in food products” to the end to confirm students' conclusions about the existence and absence of protein‑containing products..

5. At the end of the lesson, the teacher asks the students to look at the summarizing presentation about the main factors that cause denaturation of proteins. The teacher also asks to do an interactive exercise - combining text into pairs (matching task)..

Summary

1. The teacher asks the students to finish the following sentences:

   • Today I learned ...

   • I understood that …

   • It surprised me …

   • I found out ...

   The teacher can use the interactive whiteboard in the abstract or instruct students to work with it

Homework

1. Listen to the abstract recording at home. Pay attention to pronunciation, accent and intonation. Learn to pronounce the words learned during the lesson.

2. Make at home a note from the lesson using the sketchnoting method.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Proteins – properties

If you direct a narrow stream of light onto a beaker with an aqueous solution of protein, you'll notice the dispersion of light. This phenomenon is called the Tyndall effect, and indicates that the egg white's protein forms a colloidal solution with water.

What are the properties of the egg white protein solution?

The observed process of precipitation of sediment is called coagulation. In this case, the process turned out to be reversible – after adding water, the sediment dissolved. An example of reversible coagulation is salting out. Reversible coagulation also occurs under the influence of low temperatures. Why did this happen?

When a protein is salted out, its spatial structure is not affected. Therefore, it is possible to transition back to its original form. Process of salting out proteins takes place under the influence of salts of certain metals, including sodium, magnesium and lithium.

Is there any permanent damage to the structure of protein, and if so, in what situation does it happen?

The observed process of irreversible coagulation of protein is denaturation. During denaturation, protein changes its structure and original properties. The factors causing denaturation of protein are as follows:

• high temperature,

• heavy metal salts (e.g. salts of copper, mercury, barium, cadmium, lead),

• concentrated acids and bases,

• ethanol.

Let's conduct experiments.

• Protein undergoes reversible coagulation under the influence of rock salt. The spatial structure of protein is not affected, and the precipitated protein sediment dissolves after water is added. This process is called salting out.

• Protein denaturation is an irreversible process during which the protein spatial structure is destroyed.

• Factors causing denaturation of protein are as follows: high temperature, heavy metal salts, concentrated acids and bases as well as ethanol.

• The biuret test and xanthoproteic reaction are colour reactions that allow to detect the presence of protein.