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Introduction to the lesson
Proteins are perhaps the most important biological molecules. Proteins assist in chemical reactions in the body, they are essential components in cell surface membranes, they provide the body with oxygen, they protect the body from disease, they give the body strength, and they determine skin colour. In chapter 6 you will learn that DNA (which makes you you) is really just a pattern for joining together amino acids to make proteins. It is very important, therefore, to know the structure of proteins. In this lesson you will learn the different structures of proteins -- primary, secondary, tertiary, quarternary. Learn these well as they will be tested in the exam and are foundational to your understanding of proteins. In chapter 6 you will learn in more detail the actual process of joining amino acids to create proteins.
Functions of proteins:
Read the section under the heading "Proteins" on p.39 of your text book.
Learning Activity 1
Answer the following question in your exercise book.
- Name the 8 functions of proteins mentioned in the text.
The basic structure of protein – the amino acid
Read the section under the heading "Amino acids" on p.39 of your text book.
Study Fig. 2.16 on p.39. Note the amino acid is made of five essential parts:
- There is the central carbon atom called the “alpha carbon”
- To the left of the alpha carbon in the amine (amino) group – this has the nitrogen atom (N)
- To the right is the carboxylic acid group
- Below (or above) is a hydrogen atom
- Above (or below) is the R-group. The R group varies in different amino acids. There are 20 naturally occurring amino acids which are shown in Appendix 1 of the Coursebook
Learning Activity 2
Answer the following questions in your exercise book.
- Draw an amino acid.
- What 5 elements make up an amino acid?
The Peptide bond
Read the section under the heading "The peptide bond" in your text book (p.39-40)
Learning Activity 3
Answer the following questions in your exercise book.
Study Fig. 2.17.
- Describe a peptide bond.
- Where in living cells are amino acids joined together to form polypeptides?
- How is this reaction controlled?
- Where are polypeptides broken in the human body?
The structure of protein
Read the section on the structure of proteins ("Primary structure" to "Quarternary structure") on p.40-42 of your text book.
Learning Activity 4
Answer the following questions in your exercise book.
- What is meant by the primary structure of protein?
- What is meant by the secondary structure of protein?
- Describe two different forms of secondary structures of protein
- What is meant by the tertiary structure of protein?
- Name and describe briefly the four bonds that keep proteins folded in their precise shapes (see Figure 2.22)
- What is the quaternary structure of protein?
Globular and fibrous proteins
Read the section under the heading "Globular and fibrous proteins" in your text book (p.43-45).
Learning Activity 5
Answer the following questions in your notebook.
- Fibrous and globular are examples of what level of protein structure?
- Describe a globular protein with reference to its shape and the arrangement of the hydrophilic and hydrophobic groups
- Give an example of a globular protein
- Describe a fibrous protein and give two examples
- What is haemoglobin?
- Describe the structure of haemoglobin
- Describe the change in structure in haemoglobin in a person with sickle cell anaemia. What is the effect of this change in structure? (see Figure 2.25)
- Describe how haemoglobin can carry oxygen?
- What is collagen?
- Describe the structure of collagen
- Describe the strength of collagen fibres. What about the structure of collagen makes it so strong?
Testing for the presence of protein
Read Box 2.4 "Testing for the presence of proteins" on p.44 of your text book.
Learning Activity 6
In your exercise book, explain how you would test for protein.
Definitions and review
Definitions
- Amino acids
- Amine group
- Carboxylic acid
- R group
- Peptide bond
- Dipeptide
- Polypeptide
- Protein
- Primary structure
- Secondary structure
- Tertiary structure
- Quarternary structure
- Disulfide bonds
- Ionic bonds
- Hydrophobic interaction
- Globular protein
- Fibrous protein
- Haemoglobin
- Haem group
- Prosthetic group
- Collagen
Mindmap
Add this section to your chapter two mindmap.