Essential idea: Proteins have a very wide range of functions in living organisms.

One of the central ideas in Biology is that structure dictates function. Above you can see insulin in its secondary, tertiary and quaternary structures. Polypeptides vary hugely in the combination and number of amino acids that they are composed from. Even if we consider a single polypeptide it's properties, and hence it's function, would vary greatly depending on it's level of structure. Insulin can exist in all these forms, but the active form, which controls blood glucose levels, is a the tertiary structure.

Understandings applications and skills:

2.4.U1 Amino acids are linked together by condensation to form polypeptides.
2.4.U2 There are 20 different amino acids in polypeptides synthesized on ribosomes. [Students should know that most organisms use the same 20 amino acids in the same genetic code although there are some exceptions. Specific examples could be used for illustration.]
2.4.U3 Amino acids can be linked together in any sequence giving a huge range of possible polypeptides.
2.4.U4 The amino acid sequence of polypeptides is coded for by genes.
2.4.U5 A protein may consist of a single polypeptide or more than one polypeptide linked together.
2.4.U6 The amino acid sequence determines the three-dimensional conformation of a protein.
2.4.U7 Living organisms synthesize many different proteins with a wide range of functions.
2.4.U8 Every individual has a unique proteome.
2.4.A1 Rubisco, insulin, immunoglobulins, rhodopsin, collagen and spider silk as examples of the range of protein functions. [The detailed structure of the six proteins selected to illustrate the functions of proteins is not needed.]
2.4.A2 Denaturation of proteins by heat or by deviation of pH from the optimum. [Egg white or albumin solutions can be used in denaturation experiments.]
2.4.S1 Drawing molecular diagrams to show the formation of a peptide bond.
[Text in square brackets indicates guidance notes]

Presentation and notes

The presentation is designed to help your understanding. The notes outline is intended to be used as a framework for the development of student notes to aid revision.
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Vocabulary

Correct use of terminology is a key skill in Biology. It is essential to use key terms correctly when communicating your understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race, speller and test to help you master the vocabulary.


Quick quiz

Quick quiz Use the BioK Quick Quiz on 2.4 Proteins (as directed) to check your understanding of the topic.
Below are the notes for this topic. Alternatively the 2.4 Proteins bottom line template can be used as a note construction template in itself or as a checklist if you are using your own or another template such as the Cornell style template.
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Activities and labs

Build your own polypeptide

Read the basic instructions (by Brian White). Additional instructions:
  • Twist the wire to make their own six- to eight-amino acid polypeptide chain.
  • Leaving three finger-widths of space between each side chain.
  • There should be more hydrophobic side chains than charged side chains, but try to include at least one anionic and one cationic side chain

You've now constructed a short polypeptide. Consider the following questions then fold your polypeptide in response:
  • What you would expect the hydrophobic side chains to do when surrounded by water?
  • What would the anionic and cationic side chains would do?

You should now have a 3D, polypeptide. What is holding the structure in place?

Lastly you are going to simulate excessive heating. Shake your polypeptide - what happens?

Some of the hydrophobic side chains should be exposed. Because of their hydrophobic nature they are attracted to the hydrophobic regions on other similarly denatured proteins, simulate this by joining polypeptides. This aggregation simulates what can happen in cooking, e.g. cooking eggs.

(Activity largely based upon this article: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1618698/)

Weblinks

Proteins
Biomolecules - The Proteins by Wisc-Online
Proteins and Protein Structure by Terry Brown
Proteins (structure, bonding and function) by June Steinberg
Amino acid structure by Biotopics
Levels of protein structure by Biotopics
Amino acids and proteins by John Kyrk
Protein Structures and Protein Folding by John Gianni
Life Cycle of a Protein by Sumanas

Bonding
Amino acid condensation and Dipeptide hydrolysis by Biotopics
Peptide bond formation by Mr T (i-biology)

Denaturation
Protein Denaturation by McGraw and Hills

Nature of science

Looking for patterns, trends and discrepancies—most but not all organisms assemble proteins from the same amino acids. (3.1)

Refer to 2.4.U2 could research and discuss the following with students as a summary activity:
  • To what extent is the statement above true?
  • What meaning could be derived from this pattern?
  • Are there any discrepancies and what is the meaning of the discrepancies?

International-mindedness

Variation in the prevalence of different health problems around the world could be discussed including obesity, dietary energy deficiency, kwashiorkor, anorexia nervosa and coronary heart disease

Theory of knowledge

. There are conflicting views as to the harms and benefits of fats in diets. How do we decide between competing views?
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