13.2 Applications and skills

13.2.4 Technology in medicine (HL)

Advances in scientific research follow improvements in technology. This is a common theme in the nature of science. Which technologies have been important in this topic?

Innovations such as ELISA and DNA microarray have allowed scientists to diagnose and treat different kinds of disease.

Try it!

  • Make a list of all the diseases that you have learned about in your IB biology course. Classify them as either i) autoimmune, ii) inherited, iii) infectious or iv) degenerative.
  • Do any of the categories overlap? Which of these diseases can be detected and/or treated using the technologies you have learned about in this topic?

Skill: Analysis of a simple microarray

  • We have learned that DNA microarray is used to identify genetic markers of disease.
  • DNA microarray can also be used to identify how disease affects gene expression. All cells from the same species have the same number and type of genes, but disease may cause certain genes to be expressed more (up-regulation) or less (down-regulation) than normal.
  • The microarray below shows the results when the genetic material of two samples (one healthy, one cancerous) is compared.

Figure 13.2.4a – Comparing gene expression in healthy and diseased cellsFigure 13.2.4a – Comparing gene expression in healthy and diseased cells

  • In the experiment, healthy cells were labelled with green fluorescence, and cancerous cells were labelled with red fluorescence.
  • The results may be interpreted as follows:

Observation

Interpretation

No dot

No hybridisation at this locus. This gene is not expressed by either healthy or cancerous cells.

Coloured dot

Locations where cDNA hybridised. Genes are being expressed.

Red dot

More gene expression in cancer cells than in healthy cells at this locus. Cancer may upregulate the expression of these genes.

Green dot

More gene expression in healthy cells than in cancerous cells at this locus. Cancer may down-regulate the expression of these genes.

Yellow dot

Equal gene expression by both samples (red and green light combine to make yellow). Cancer may have no effect on the expression of these genes.

  

Skill: Interpretation of ELISA test

  • There are different types of ELISA. The method you learned in 13.1.4 is called the ‘sandwich ELISA’ and tests for the presence of antigen. It is very effective, but a high degree of skill is required to get clear results.
  • Another type of ELISA, called ‘indirect ELISA’, tests for the presence of antibodies in the blood. This test requires a secondary antibody to bind to the target protein. It also requires that the person has already formed an immune response to the disease. (i.e. early detection is not possible).

Figure 13.2.4b – Indirect ELISA tests for the presence of antibodies in the bloodFigure 13.2.4b – Indirect ELISA tests for the presence of antibodies in the blood

  • Different types of ELISA are more appropriate for different purposes, but in all types of tests a colour-change indicates positive results.

Figure 13.2.4c – Colour change indicates a positive result in ELISAs.Figure 13.2.4c – Colour change indicates a positive result in ELISAs.

  • After a positive result is achieved, the microplate may be placed into a machine that determines the concentration of antigen (or antibody) by measuring the optical density of the samples in each well.
  • If more light is absorbed, (i.e. darker colour), the concentration of antigen (or antibody) is high.

Try it!

  • Outline the steps for a sandwich ELISA for the detection of antigens.
  • Compare ELISA protocols for the detection of antigens, and of antibodies.

Nature of Science

Figure 13.2.4d – Scientific researchFigure 13.2.4d – Scientific research
Developments in scientific research follow improvements in technology – innovation allows for the diagnosis and treatment of disease.

Figure 13.2.4e – Fluorescent cDNAFigure 13.2.4e – Fluorescent cDNA
Fluorescent cDNA lights up when it is hybridised to the DNA on the microarray chip.

Food for thought

What other types of cells could a DNA microarray be used to compare?

Figure 13.2.4f – Microplate readerFigure 13.2.4f – Microplate reader
Concentration of antibody is determined by an absorbance reader.