Proteins 2.4

This topic is all about proteins which are the most diverse of molecules. They are built from just twenty amino acids and show a huge variety of forms, from spider's silk to insulin hormones.

Key words

Learn and test your biological vocabulary for 2.4 Proteins using these flashards 

Clean sweep - quick revision through the whole topic

These slides summarise the essential understanding and skills in this topic. 
They contain short explanations in text and images - good revision for all students.

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Video tutorial

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Revision summary list for 2.4 Proteins

  • Amino acids are linked together by condensation reactions to form a di-peptides and polypeptides.
  • Genes and mRNA strands code for 20 different amino acids which are built into polypeptides on ribosomes.
  • Amino acids can be linked together in any sequence (coded for by genes) giving a huge range of possible polypeptides.
  • A protein may be a single polypeptide or more than one polypeptide joined together.
  • The three-dimensional shape of a protein is determined by the sequence of amino acids.
  • Living organisms synthesize many different proteins with a wide range of functions (not structure)
    e.g. Rubisco, insulin, immunoglobulins, rhodopsin, collagen & spider silk.
  • Every individual has a unique proteome.
  • Proteomics and the production of proteins by cells cultured in fermenters
    offer many opportunities for the food, pharmaceutical and other industries
    (a utilisation)
  • Ability to draw molecular diagrams of peptide bond formation.

Revision mind map

These diagrams summarise the main sections of topic 2.4.
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Review questions

This is a self marking quiz containing questions covering the topic outlined above.
Try the questions to check your understanding.


Apart from the elements carbon, hydrogen and oxygen, what are the elements most commonly found in proteins?

Proteins and their amino acids are made from Carbon Hydrogen Oxygen and Nitrogen. A few amino acids also contain sulfur.


What type of molecule is formed from amino acids by a single condensation reaction?

Condensation reactions join the -OH of the carboxyl group to the NH- of an amine group.
This forms a peptide bond and a dipeptide.


Proteins are made from long chains of amino acids.

One example is the hormone insulin.

Which part of a cell determines the order of the amino acids in the protein Insulin?

The Primary structure of proteins (the order of the sequence of the amino acids in the polypeptide chain) is determined by genes in the nucleus. (i.e. DNA)


What type of bonds mostly hold together the 3D shape of a protein?

Hydrogen bonds hold the 3D shape of proteins together.
This is a weaker bond than covalent bonds, so heat and extremes of pH can denature enzymes.


The function of a protein depends upon its shape.

Structural proteins often have a specific shape.

Which of the following proteins are most likely to have a structural function?

B is collagen - the most common protein in humans, it makes up bone, tendons, skin and many more structures.

In multicellular organisms the cells differentiate and become specialised.
What effect does the process of differentiation have on the proteome and the genome of the cells?

Although the genomes of cells in an organism are almost exactly the same the proteome of a cell depends on the expression of specific genes, and can be quite differen from tissue to tissue.

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