2.5 How Threshold Concepts Can Help You Tackle Big Problems

The videos below illustrate the power of learning key threshold concepts. These presentations were made by students as part of an introductory biology course (They were recorded as they demonstrated a high degree of accomplishment in this task, and they agreed to be filmed. We are very grateful to them — it is not easy to present in front of a camera and all of your lecturers!).

For the exercise, students were asked to tackle a complex idea in biology and present it to their peers. The topics were chosen for the students and were deliberately aligned with a key threshold concept in biochemistry/molecular biology but deliberately made much more challenging by extending the idea into current research.

The students started this assignment in the second week of their university studies and presented before the end of semester. Most were not biochemistry or molecular biology majors, and many had very little or no previous experience studying biology!  However, despite their lack of experience, by starting with a major threshold concept and extending from there, they were able to engage with primary literature (read scientific research papers), deal with equivocal data (conflicting ideas) and often think about the implications of the research for future innovations and their impact to society.

Try watching the videos linked below even if you are very new to the topics — you might come away with a preliminary understanding which will help when you encounter these the underlying threshold concepts again. Also, if you are new to studying, it is extremely likely that you will have to make oral presentations yourself in your course at some point. A good way to learn how to do this is to watch others. If opportunity exists where you study, go to some scientific presentations or watch presentations from research students. Initially, it is normal to find these daunting and difficult to follow but persevere. The best presenters are adept at making their content clear and accessible to a wide audience. Take note of how they do this!

Here, take note of how the presenters have structured their talks, approached their problem and conveyed information — bearing in mind that these students had not yet completed one semester of studies! While watching these, ask yourself:

• What worked well in the presentation (which parts did you understand?) and possibly what they could have improved?
• Was sufficient background information presented for you to follow?
• Did the ideas flow well?
• What did you find interesting and what would you like to know more about?

Conservation of Protein Structure

This topic was based on the threshold concept: “The tertiary structure of proteins is more evolutionarily conserved than the primary structure.”

Students who presented on this were asked to explain why they would expect the statement above to be true. In their explanation they were asked to describe the hierarchy of protein structure and using examples, relate protein structure to function. To describe how proteins (or domains) can be grouped into families and explain the difference between homologous and analogous proteins (or domains).  And finally, to discuss the major mechanisms by which new protein functions evolve.

Watch the presentations from Belle and Carah to learn about this topic. Take note of the similarities and differences in these talks. Think about the different approaches they have used to convey similar information here. In your own studies finding an alternate explanation or a different analogy which works for you can make a big difference to your learning.

Defining a Gene

This topic was based on the threshold concept: “The unit of genetic information in a nucleic acid that specifies a functional macromolecular product (protein or RNA) is called the gene.” (See Chapter 4.1 What is a gene?)

This might initially seem like a simple idea!  But here students were asked to consider the neo-classical hypothesis of the gene which states that “one gene leads to one mRNA which leads to one polypeptide”. They were asked to comment on this and how our advances in understanding molecular biology made defining a gene difficult.  To discuss mRNA splicing, and in particular how alternative splicing increases the complexity of gene expression.  To consider why alternative splicing is important for adaptive evolution.  And finally, if our advances in our understanding of gene expression mean we need to redefine the gene.

Watch the presentations from Shakira and Gabriel to learn about this topic.  Again, take note of the similarities and differences in these talks.  Though there is some overlap between the two, Shakira has focused a lot on the diversity of gene products resulting from alternative splicing while Gabriel focuses more on gene regulation – valid when considering how to define a gene!  Gabriel also provides a timeline of how the idea of a gene developed – recapitulating discoveries can often provide a greater understanding than jumping to the final answer!

Compartmentalization in Cells

This topic was based on the threshold concept: “Eukaryotes have internal membranes (compartmentalization) including a nucleus while prokaryotes do not.  This has functional implications for many processes including cell division and gene expression.” (See Chapter 3.2 The Cellular Basis of Life)

Students who presented on this were asked to explain why compartmentalization is important for all life. There is still compartmentalization in bacteria, but it is protein-based.  Explain how this works.  What are bacterial microcompartments?  What are encapsulin nanocompartments?  What are their functions?  In what ways are they functionally analogous to eukaryotic organelles and how do they differ? How are they studied and why might they be biomedically relevant?

Watch the presentation from Urvi to learn about this topic.

Endosymbiosis

This topic was based on the threshold concept: “Endosymbiosis is the leading evolutionary theory on the origin of eukaryotic cells from prokaryotes.”

Students who presented on this were asked to focus either plastids or mitochondria and discuss the evidence that they arose from an endosymbiotic event.  They were asked to discuss their chosen organelle’s need for a remnant genome and explain what functional gene products it coded for.  And finally, to compare the genome of their organelle with its proteome and consider how its proteins are imported.

Watch the presentations from Gabrielle (who focuses on plastids) and Mujiba (who focuses on mitochondria).  Despite focusing on two different organelles, you might notice there some very similar ideas. It is important when studying biology to see through the complexity and start noticing patterns!

Chemoautotrophs

This topic was based on the threshold concept: “Biological systems use energy captured from the environment in biosynthetic pathways.”

Students who presented on this were asked to consider energy capture by chemoautotrophic organisms.  All organisms capture and process energy from the environment.  Most do this with energy emanating directly from the sun (photosynthesis) or from other organisms (e.g., carbohydrates). However, chemoautotrophic organisms can capture energy from simple inorganic compounds such as H2 or those containing Fe2+.  Students were asked to explain, using a specific example, how chemoautotrophs are able to use simple inorganic compounds to fix carbon, why it is postulated that life had a chemoautotrophic origin and to discuss the importance of ‘dark carbon fixation’ to the carbon biogeochemical cycle.  And finally, to consider how chemoautotrophs could play a role in mitigating climate change.

Watch the presentations from Innila and Nik who have alternate ways of explaining the amazing chemistry of these organisms and how they thrive in environments reminiscent of a primordial Earth!