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Extension activity: Help learners explore the diversity of phospholipids and the reason for this diversity, such as addition of other water-soluble groups to the phosphate group.
2.3 Proteins
KC2
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2.3 1 Describe and draw the general structure of an amino acid and the formation and breakage of a peptide bond.
2.3.2 Explain the meaning of the terms primary structure, secondary structure, tertiary structure and quaternary structure of proteins.
2.3.3 Describe the types of interaction that hold protein molecules in shape:
hydrophobic interactions
hydrogen bonding
ionic bonding
covalent bonding, including disulfide bonds.
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Learners have an oversimplified idea of what is meant by ‘protein.’ Explain that proteins achieve a very wide range of functions in organisms. On the class board, show a range of these, including (but not limited to): antibodies, hormones, enzymes, collagen (connective tissue) and keratin (hair), muscle proteins, retina photoreceptors and milk protein. Learners decide, in pairs, how to categorise these molecules. (F)
Learners work in pairs to produce a model of insulin. Share the primary structure of the two polypeptides and where they are attached by disulphide bonds. Learners prepare 20 different paper shapes of various colours to represent the different amino acids. Provide a key to inform learners which pieces of paper represent which amino acid. (I)
Learners work in groups to make a concept map, mind map or other form of graphic organiser for the types of bond found in each level of protein structure. This is useful preparation for interpreting the content of the next section of this subtopic. (F)
Extension activity: Construct a table that compares the types of bond found in the tertiary structure of proteins – the atoms the bonds form between, and the relative strength of the bonds. Also construct a table to compare fibrous and globular proteins.
Ask a carefully chosen series of questions to elicit higher-order thinking skills among learners. One option is to ask them to compare key terms, to reinforce their knowledge of key definitions. (F)
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2.3.4 State that globular proteins are generally soluble and have physiological roles and fibrous proteins are generally insoluble and have structural roles.
2.3.5 Describe the structure of a molecule of haemoglobin as an example of a globular protein, including the formation of its quaternary structure.
2.3.6 Relate the structure of haemoglobin to its function, including the importance of iron in the haem group.
2.3.7 Describe the structure of a molecule of collagen as an example of a fibrous protein, and the arrangement of collagen molecules to form collagen fibres.
2.3.8 Relate the structures of collagen molecules and collagen fibres to their function.
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Learners work together in small groups to produce a poster to show the similarities and differences between haemoglobin and collagen. Encourage them to show how these proteins are representatives of globular and fibrous proteins respectively. You could extend this activity into the next lesson by holding a ‘marketplace’ activity: one member of each group stands by their poster and offers an explanation to other groups as they move around the room. Help learners provide feedback to each other in in a respectful way. Encourage learners to focus on key Syllabus statements, including the importance of iron in the haem group in haemoglobin, and the arrangement of collagen molecules to form collagen fibres.
Present a series of questions on the board. Give learners 5 minutes to write down all the key terms they feel are relevant in their answers. Then model how to incorporate relevant key words into clear, exam-style answers. (F)
Prepare a short, written passage that summarises the content of this subtopic. Include between five and ten spelling mistakes and conceptual errors. Learners spot and circle as many mistakes as possible, and offer corrections. An example would be learners’ common use of collagen polypeptides and collagen fibres as interchangeable terms. Three collagen polypeptides, which have a helix structure, together form a triple helix called a collagen fibre. (F)
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2.4 Water
KC2
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2.4.1 Explain how hydrogen bonding occurs between water molecules and relate the properties of water to its roles in living organisms, limited to solvent action, high specific heat capacity and latent heat of vaporisation.
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Show learners a demonstration to illustrate the unique properties of water. Learners engage in a ‘think, pair, share’ activity to try to explain why water behaves in this way. Examples include:
Carefully balance a pin on the surface of a large beaker of water to demonstrate the surface tension of the liquid. Add a drop of detergent to reduce the surface tension and observe the pin sink immediately.
Set up two clamped, inverted round-bottomed flasks and cover one with a wet cloth. The temperature inside this flask will fall relative to the other. This illustrates the high latent heat of vaporisation of water.
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