Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Giant Molecules (Proteins)
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Giant Molecules (Proteins)
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Subject: Chemistry
Class: Senior Secondary 3
Term: 1st Term
Week: 7
Theme: Chemistry Of Life
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list sources of Protein give examples of proteins identify aminoacids as the building.blocks of proteins state the physicaland chemicalproperties of proteins Carry out confirmatory test for proteins state the uses of proteins
Chemistry Of Life and "protein" in terms of their molecular structure and size.
3. A chef boils an egg. Explain, in terms of protein structure, why the egg white changes from a clear liquid to a solid white mass.
4. You are given three unknown solutions (A, B, and C). Solution A gives a yellow precipitate that turns orange when concentrated nitric acid and then ammonia are added. Solution B shows no color change with Biuret reagent. Solution C gives a violet color with Biuret reagent. Identify which solution(s) likely contain protein and justify your answer for each.
5. Apart from building and repairing tissues, state three other vital functions of proteins in the human body.
6. Draw the general structure of an amino acid and identify the peptide bond in a dipeptide formed from two generic amino acids.
7. Name the specific test used to detect the presence of peptide bonds in a sample and describe the color change observed if positive.
8. What is meant by the "amphoteric nature" of proteins? Explain how this property is beneficial to living organisms.
9. A protein solution is treated with a heavy metal salt like lead acetate. What observable effect would this have on the protein, and why?
1
0. Suggest two industrial applications of proteins, providing a specific example for each.
6. Evaluation and Assessment Formative Assessment: Class Discussion and Q&A: Observe student participation in discussions about protein sources and functions. Ask targeted questions to gauge understanding of amino acid structure and peptide bond formation.
Practical Observation: During the confirmatory tests, monitor students' adherence to procedures, accurate observation, and ability to infer results.
Mini Whiteboard Activities: Ask students to draw an amino acid or outline a test procedure on mini-whiteboards for quick checks. Summative Assessment (aligned to Evaluation Guide):
1. Give examples of proteins (2 marks): Name two specific proteins found in the human body and state one function for each.
Marking Scheme: 1 mark for each correct protein name and function (e.g., Haemoglobin – oxygen transport; Keratin – structural support).
2. Describe the structure of proteins and identify amino acids as the building blocks of proteins (4 marks): a. What are the basic monomeric units of proteins? (1 mark) b. Draw the general structure of one of these monomeric units, clearly labelling its four main parts. (3 marks)
Marking Scheme: a. Amino acids (1 mark). b. Correct diagram with all four parts labelled (amino group, carboxyl group, hydrogen, R-group) (3 marks).
3. List the physical and chemical properties of proteins (4 marks): State two physical properties and two chemical properties of proteins.
Marking Scheme: 1 mark for each correct property.
Physical: High molecular mass, solubility (colloidal), denaturation, amphoteric nature, optical activity. (Any 2)
Chemical: Hydrolysis, reactions of amino/carboxyl/R-groups. (Any 2)
4. Enumerate the uses of proteins (3 marks): Mention three significant roles or uses of proteins in living organisms or industry.
Marking Scheme: 1 mark for each correct use (e.g., structural, enzymes, hormones, transport, immune defense, food industry, pharmaceuticals).
5. Test for proteins (7 marks): You have an unknown solution suspected to contain protein. a. Outline the procedure for performing the Biuret test on this solution. (3 marks) b. State the expected observation if protein is present in the Biuret test. (1 mark) c. Describe another confirmatory test for proteins that involves heating with an acid, stating the reagents used and the positive observation. (3 marks)
Marking Scheme: a.
Correct steps: Add sample, add NaOH, add CuSO4 dropwise (3 marks). b. Violet/purple coloration (1 mark). * c.
Xanthoproteic test: Reagents (conc. HNO3, NH4OH/NaOH) (1 mark), procedure (heat, cool, add alkali) (1 mark), positive observation (yellow turning orange) (1 mark).
OR Millon's test: Reagent (Millon's), procedure (heat), positive observation (red ppt/color).
OR Heat Coagulation: Reagent (heat, dilute acid), procedure (heat, add acid, reheat), positive observation (coagulum/precipitate).
Total Marks: 20 marks
7. Real-life Applications / Integration
1. Nutrition and Public Health in Nigeria: Understanding proteins is crucial for addressing malnutrition, particularly Kwashiorkor (protein deficiency) prevalent in some rural areas of Nigeria where staple b. Violet/purple coloration (1 mark). c.
Xanthoproteic test: Reagents (conc. HNO3, NH4OH/NaOH) (1 mark), procedure (heat, cool, add alkali) (1 mark), positive observation (yellow turning orange) (1 mark).
OR Millon's test: Reagent (Millon's), procedure (heat), positive observation (red ppt/color).
OR Heat Coagulation: Reagent (heat, dilute acid), procedure (heat, add acid, reheat), positive observation (coagulum/precipitate).
Total Marks: 20 marks
7. Real-life Applications / Integration
1. Nutrition and Public Health in Nigeria: Understanding proteins is crucial for addressing malnutrition, particularly Kwashiorkor (protein deficiency) prevalent in some rural areas of Nigeria where staple diets might be carbohydrate-heavy. Knowledge of protein sources (affordable local legumes like beans, groundnuts, soy) allows for balanced meal planning and dietary advice campaigns. For instance, promoting the consumption of akara and moi-moi (bean-based products) or incorporating soy flour into garri or fufu can improve protein intake.
2. Food Processing and Preservation: Proteins play a vital role in the Nigerian food industry. For example, enzymes (which are proteins) are used in brewing traditional drinks like burukutu or pito. Gelatin (a protein derivative) is used in confectioneries and as a gelling agent. The coagulation property of proteins is exploited in making local cheeses (wara from milk) or in the processing of ogiri or dawa dawa (fermented condiments), where protein breakdown products contribute to flavor and texture.
3. Agriculture and Animal Husbandry: In agriculture, understanding protein requirements for different crops and livestock is key. Farmers learn about high-protein feeds for poultry, fish (aquaculture, e.g., tilapia, catfish farming), and cattle to ensure optimal growth and productivity. The protein content of crops like soybeans or groundnuts makes them valuable cash crops and sources of animal feed supplements, contributing to the nation's economy.
8. Differentiation, Remediation and Extension Differentiation Strategies: Visual Aids: Utilize diagrams, charts, and molecular models to illustrate amino acid structure, peptide bond formation, and protein folding. Use real-life food samples and lab reagents during demonstrations.
Group Work: Organize students into small groups for practical sessions and discussions, allowing peer learning and support. Assign roles within groups to ensure participation from all learners.
Tiered Activities: Provide scaffolded worksheets for practical tests, guiding struggling learners with step-by-step instructions and observation charts, while more capable learners can be challenged with explaining the chemical principles behind each test.
Remediation for Struggling Learners: Simplified Concepts: Focus primarily on identifying protein sources, the basic amino acid structure (showing only the amino, carboxyl, H, and R groups without delving into specific R-group chemistry), and the most common protein test (Biuret test).
Repetitive Practice: Provide additional practice in identifying protein-rich foods and performing simple protein tests. Use flashcards for amino acid parts or protein examples.
One-on-One Support: Offer individualized attention to clarify misconceptions, using simpler language and analogies (e.g., "amino acids are like LEGO bricks, and proteins are the complex structures built from them").
Pre-made Models/Diagrams: Provide pre-drawn diagrams of amino acid and peptide bond formation for labelling practice rather than freehand drawing initially.
Extension for High-Achieving Learners: Advanced Protein Structure: Encourage research into the different levels of protein structure (primary, secondary, tertiary, and quaternary) and how these levels influence protein function and stability.
Enzyme Kinetics and Specificity: Investigate how proteins act as enzymes, exploring concepts like active sites, enzyme-substrate specificity, and factors affecting enzyme activity (temperature, pH, inhibitors).
Protein Synthesis: Explore the process of protein synthesis from DNA to RNA to protein (central dogma of molecular biology).
Genetically Modified Proteins: Research examples of genetically engineered proteins used in medicine (e.g., recombinant insulin, vaccines) or agriculture (e.g., pest-resistant crops).
Case Study Analysis: Assign a research project on a specific protein deficiency disease in Nigeria, its biochemical basis, and possible solutions. supervision. Discuss observations and inferences from the practical tests. Contribute to discussions on the importance and uses of proteins. Answer questions posed by the teacher and participate in group activities.
4. Guided Practice (With Solutions)
Question 1 (Sources & Examples): A Nigerian family is planning their weekly meals to ensure adequate protein intake. Suggest three animal-based and three plant-based protein sources commonly available in Nigerian markets. Also, name one specific protein found in humans and state its function.
Solution 1: Animal-based protein sources:
1. Beef (eran malu) or Goat meat (eran ewure)
2. Mackerel fish (titus) or Tilapia
3. Eggs Plant-based protein sources:
1. Beans (e.g., cowpea for moi-moi or akara)
2. Groundnuts (epa)
3. Soybeans (or products like wara) Specific protein in humans and its function: Haemoglobin: Transports oxygen from the lungs to the body tissues.
Keratin: Provides structural support in hair, nails, and outer skin layers.
Insulin: Regulates blood glucose levels. (Any one of these, or other valid examples, is acceptable)
Question 2 (Amino Acids & Structure): Describe the fundamental structure of an amino acid, clearly labelling its key functional groups. Explain how two amino acids combine to form a dipeptide, mentioning the type of bond formed and the byproduct.
Solution 2: Fundamental Structure of an Amino Acid: An amino acid consists of a central carbon atom (alpha-carbon) bonded to:
1. An amino group (-NH2)
2. A carboxyl group (-COOH)
3. A hydrogen atom (-H)
4. A variable R-group (side chain), which determines the specific properties of the amino acid. (Drawing the structure with labels would be ideal) ``` H | H2N -- C -- COOH | R ``` Formation of a dipeptide: Two amino acids combine via a condensation reaction. The carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH2) of another amino acid. This reaction involves the removal of a water molecule (H2O). The resulting bond formed between the carbon of the carboxyl group and the nitrogen of the amino group is called a peptide bond. The product is a dipeptide.
Question 3 (Properties & Tests): A student is given an unknown food sample suspected to contain protein. a. Describe one distinct physical property of proteins that could be observed by gently heating the sample. b. Outline the procedure for performing the Biuret test on this sample, and state the expected observation if protein is present. c. Suggest one safety precaution when performing the Xanthoproteic test.
Solution 3: a.
Physical property: Upon gentle heating, many proteins undergo denaturation and coagulation, becoming insoluble and forming a precipitate or a turbid solution. For example, if the sample is a liquid protein solution, it might turn opaque or solidify. b.
Biuret Test Procedure and Observation: Procedure:
1. Add about 2 cm3 of the unknown sample into a test tube.
2. Add an equal volume (2 cm3) of 10% Sodium Hydroxide (NaOH) solution. Shake well.
3. Add a few drops (2-3) of 0.5% Copper(II) Sulphate (CuSO4) solution drop by drop, shaking gently after each drop.
Expected Observation: If protein is present, a violet or purple coloration will appear. c.
Safety Precaution for Xanthoproteic Test: Concentrated nitric acid (conc. HNO3) is highly corrosive.
Therefore, wear safety goggles to protect eyes from splashes and handle the acid under a fume hood or in a well-ventilated area to avoid inhaling fumes. Avoid direct contact with skin and clothing.
5. Independent Practice (Questions Only)
1. List four distinct food items commonly consumed in Nigeria that are excellent sources of protein.
2. Differentiate between the terms "amino acid" and "protein" in terms of their molecular structure and size.
3. A chef boils an egg. Explain, in terms of protein structure, why the egg white changes from a clear liquid to a solid white mass.
4. You are given three unknown solutions (A, B, and C). Solution A gives a yellow precipitate that turns orange when concentrated nitric acid and then ammonia are added. Solution B shows no color change with Biuret reagent. Solution C gives a violet color with Biuret reagent. Identify which solution(s) likely contain protein