Supressor tRNA

What was the point?


Well, there are a couple. The first is to think about the complexity of this process and, by extension, all processes. No important molecule in your cells, as far as I can think of, works alone. The fact that all proteins, DNA and RNAs etc interact with other proteins, DNA or RNA means that mutations can effect the interface of those interactions. That also means that all proteins (and some RNA and DNA) can evolve compensatory changes. You can learn about those interactions by examining compensatory mutations.
In this case, we learned more about an RNA/RNA interaction. A mutation that changed the primary structure of the mRNA led to premature termination of translation and a truncated protein. A second mutation to the DNA encoding a tRNA allowed the stop codon to be read by a new anticodon that matched it (with a tyrosine tRNA in this case, resulting in an altered, but functional protein).
But it can happen at the level of protein-protein interaction. This is an important concept for evolution: Think about the fact that there are so many protein kinases, each of which is very similar in structure to the others, that bind to and phosphorylate their own specific target proteins. Often those target proteins are also similar to each other. Reflect back on some of the signaling cascades at which we looked earlier in the year, or the cyclin/CDK pathways.
We've learned that genes can be moved around, new copies of domains or whole genes can be moved around. You will see more of this, but you have already encountered such "gene families."
This is a powerful mechanism in evolution. You can get a duplication of a large stretch of DNA that encodes several proteins that interact with each other to perform a task, and the evolve changes over time that allow them to work to perform a related task by altering their interacting domains.

Redundancy is useful


Another important point is that redundancy is useful…it's good to have multiple copies of important things. I've run out of ideas for being more redundant here.
One reason for this is for the cell to be resilient under difficult conditions. It's also important to remember that every process in a cell is imperfect. Nothing happens correctly 100% of the time. There are mis-reads of DNA, mistakes at the Ribosome…cells should be able to withstand the level of errors that are invariably going to happen. Then, often, there are backup systems. In this case, it turns out that most genes have several in-frame stop codons after the first one. This implies that "read through" of stop codons is a thing that happens with some frequency. Without additional stop codons, cells might make giant proteins like the ones Rohit wants to make.
Also, there is redundancy in the copies of rDNA and tDNA (those are the genes that encode rRNA and tRNA). They exist in large repeated regions…multiple copies of the same DNA repeated one after another. This is because there is a need to make a huge amount of the rRNA and tRNA.
If you start thinking about it, you might see that having genes that work together stored together in the same region of a chromosome might have some advantages for regulation. When we get to the "evolution and development" section, this concept of large duplications of genes diverging into closely related proteins with different but related jobs will be extremely important…in that case, regulating transcription of other genes.