Drawing out the structure of DNA

Anveshna Srivastava

“He who would learn to fly one day must first learn to stand and walk and run and climb and dance; one cannot fly into flying” – Friedrich Nietzsche

Learning is a progressive endeavour, where systematicity plays a significant role. One cannot write without knowing the alphabet! The order may not be rigid every time, but a systematic progression from simple to complex conceptual understanding helps the learner to see things in perspective, rather than be lost in the conundrum of conceptual network. Still, each learner is a unique individual with unique learning processes (von Glasersfeld, 2001), and it makes it difficult for the facilitators to use their discretion in using representational notations which can map on to the receptive structures of all learners.

This mapping difficulty can be alleviated to a large extent through the use of different representations which coheres with the conceptual story narrated by the facilitator. In our day to day learning interactions, texts and diagrams form the most widely used representational notations. The diagrams used are visually more appealing than the text but not so much that the learners can connect textual information with them. One of the solutions to this problem is to use multiple external representations which can help learners to complement information and processes, constrain multiple interpretations and construct deeper understanding (Ainsworth, 1999). But, a mere inclusion of more number of representations will bombard learners with too much of information, and hence it is important that learners engage with different representations used. This is possible if there is a logical progression to the introduction of these representations.

In this article, I will introduce a few representations which are simple enough to construct and which if exploited in a certain sequence can aid in the sense-making of a complex biology concept, the structure of the DNA.

The context
The Deoxyribonucleic acid (DNA) molecule has a special place amongst homo sapiens, who are probably the only species on the planet whose quest for knowledge has led to the extensive exploitation of this carrier of the units of heredity (read ‘genes’). DNA’s biological significance of being a carrier of genes has hugely contributed to not just our understanding of other biological organisms but also to the advancement of medical sciences, where humans have tremendously increased their average life span. Since the discovery of DNA’s structure in 1953 by Watson and Crick, learning fields like ‘molecular biology’, ‘biotechnology’, ‘bioengineering’, etc., have emerged to specifically tap into the various possibilities offered by this molecule.

The functional capability of DNA is governed by its wonderful structure, which is, unfortunately, given significantly less space and time in a teaching-learning environment. The situation could be understood as a ‘what is it?’ question being masked by ‘what could be done with it?’ question. The latter question is indeed more practical, engaging and thought-provoking but the point is that one can be more innovative and imaginative in answering it, if one has deeply engaged with the earlier question.

The Indian school curricula relies heavily on textbooks which may include 2-D diagrams along with the relevant text. In the context of DNA, which is a 3-dimensional molecule, a 2-dimensional textbook diagram cannot sufficiently capture its salient features. The 2-D picture may be a good starting point but if left undiscussed and unexplained, it may lead to serious misconceptions. Here comes the role of different representations.

Using different representations
In addition to imparting factual information, an introductory session has the responsibility of invoking the learner’s interest and to prepare her/him for constructing deeper understanding of the subject matter. One cannot afford to make this session boring by a non-stimulating dull lecture!

It is useful to introduce different representations in a series which moves in an ascending order. It means that a representation which has possibly the least amount of information be introduced first and so on. The logic being that familiarity with simple concepts is likely to facilitate further involvement with complex concepts, and this also ensures that learners get gradually accustomed to increasing cognitive demand.

Representations can be used both to contribute and to diagnose learners’ understanding. I will give examples for both: a) when representations are used as an aid to facilitate learners’ understanding, and b) when representations are used to assess learners’ understanding.

While facilitation
i) Model
A 2-D diagram may be used to introduce different components of the DNA structure. This will help learners to form an overview of the concept, which can be further deepened by the introduction of a basic model (as shown in the photo above).

A ‘clothespin model’ can be the basic model which highlights the features of the DNA like two stranded nature (shown by two plastic pipes), and specific base-pair bonding (shown by 4 differentially colored clothespins); the base Adenine (pink) always bonds with Thymine (yellow), and the base Guanine (green) always bonds with Cytosine (blue).

Note that this model doesn’t show detailed features like hydrogen bonds and sugar phosphate units.

The next model can focus on specific details like the sugar phosphate backbone. The ‘backbone model’ illustrates a single sugar-phosphate unit on either strand of DNA. This model depicts the attachment points of sugar-phosphate molecules, while giving the molecular details.

This model can be used to help learners appreciate covalent bonding between the two units which forms the basis for phosphodiester bonding. Further, molecular structure of the bases can be made and formation of one nucleotide pair be shown.

Finally, a completely molecular 3-D model can be shown to learners to appreciate the different kind of atoms and bondings involved in its formation.

This particular model is made from wires and differentially coloured plastic pipes. Each colour stands for a specific atom, viz., black for carbon and red for oxygen. The hydrogen bonds (not clearly visible) are shown with opaque plastic pipes and the other covalent bonds are shown with transparent plastic pipes.

The above models may be constructed by students working in groups, where each group may be given a 2-D picture of the structure. Apart from being engaged in the building of the DNA structure, this exercise would also enable the learners to re-visit their chemistry concepts of valency and bonding.

ii) Gesture
Yes, gestures! We have all use gestures, sometimes consciously but mostly unconsciously. A path-breaking research has shown that gestures could have even more powerful influence on the thought process than the action itself (Goldin-Meadow & Beilock, 2010).

The orientation of DNA base pairs is actually similar to the orientation of steps in a ladder, is known through text but is not understood well. Positioning the palm such that the flat surface lies perpendicular to the sugar-phosphate backbone gives the correct orientation of the DNA base pairs. This gesture can, thus, help learners to connect the ladder analogy with their own mental visualization of the orientation. This ‘palm gesture’ may be used against the ‘backbone model’ of the DNA.

Also, other gestures may be designed by learners and facilitators to aid mental visualization of other structural details.

Post facilitation
i) Concept-map
Concept-mapping is a tool which lets the learner re-visit and explicate the conceptual connections that she/he has formed while learning about the concept. It also lets the facilitator know at what points the learner is faltering and requires assistance.

Learners can be given certain concepts (viz., ‘purines’, ‘nitrogenous bases’) and can then be asked to build connections between those concepts through arrows and specific linking phrases. For instance, the concept ‘DNA’ and the concept ‘Two strands’ may be connected as – ‘’DNA’ is made up of ‘Two strands’’, where ‘is made up of’ becomes the linking phrase.

ii) Puzzle
We all get fascinated by puzzles and, hence, puzzles could be very captivating for learners to participate and engage with a specific concept. A crossword puzzle could be generated to assess learner’s conceptual associations along with the recall of specific terms. Unlike, concept-maps, puzzles can be used as a quick assessment tool, while raising the competitive spirits of the learners.

Discussion
It won’t take much effort to establish that the use of different systematic representations in a teaching-learning environment adds vitality to the interaction, while motivating learners to proceed to an advanced conceptual level. Along with enabling learners to push their cognitive abilities a little further with each representation, the sequencing helps them build a conceptual framework bit-by- bit such that the former connections get registered and further connections become predictable.

Even though the role of different representations seems to be obvious in supporting learning, it is useful to acknowledge that they may not cater to the requirements of every learner. Hence, the sequence of representations ought to be thought-over and improvised as per the requirements of the learning environment.

References

• Ainsworth, S. E. (1999). The functions of multiple representations. Computers and Education, 33, 131-152.
• Goldin-Meadow, S., Beilock, Sian L. (2010). Action’s Influence on Thought: The case of gesture. Perspectives on Psychological Science, 5 (6), 664-674.
• Srivastava, A., & Ramadas, J. (2013). Analogy and Gesture for Mental Visualization of DNA Structure. In Multiple Representations in Biological Education (pp. 311-329). Springer: Netherlands.
• von Glasersfeld, E. (2001). The radical constructivist view of science. Foundations of science, 6(1-3), 31-43.

The author is a research scholar at Homi Bhabha Centre for Science Education, TIFR. Her research interest includes exploring students’ understanding about the DNA structure. She can be reached at anveshna@hbcse.tifr.res.in.