Why Magnitudes Matter

fBy Joseph Maa:

Date: 6/1/2017

Hi everyone just a short post today:

I was recently reading a book and it came up that the human diploid genetic code has 6 billion base pairs. [1] Back in high school and middle school, memorizing the numbers really seemed to be more of a fun fact than pragmatic information.

Especially in middle school and high school, if you knew the information, it wouldn’t really teach you anything and would probably brand you a little bit nerdy by the rest of the students. The reasoning behind my previous conjecture is that high school biology does not expect synthesis of the information to the point where knowing information like genome size matters. (That’s why private high schools have lab courses that bridge the gap between theory and practice) [2]

Screen Shot 2017-06-01 at 7.04.16 AM.png
Figure 1: The infamous strawberry DNA experiment that everyone gets to do. Strawberries are still in season too! [3]
However, knowing the numbers really does give you a better “sense” of the scope of practice. Unfortunately, this occurs most frequently when you do research, which isn’t readily available to younger students. For example, pretend you’re a new biologist and you wanted to look to calculate the % DNA composition that our entire body is made of. In this case, knowing the mass of DNA per cell, as well as the conversion factor of 937 megabases (mega = million, hence megamillion lotteries!) is about 1 picogram (10^-12, more numbers!) is incredibly helpful. [4]

Screen Shot 2017-06-01 at 7.07.43 AM.png
Figure 2: Who would’ve thought that we had something to learn from lotteries? Apparently I still need to pay more attention to my surroundings [5]
Theoretically, that means that you could calculate the mass of DNA in a single cell. Funnily enough, in this case, since the number of actual human cells is always being debated, it would actually be impossible to say with certainty how much “human DNA” comprises a single person. In fact, since the current running ratio for bacteria:human cells is 10:1 (I’ve also linked something that argues otherwise), you’d probably find a lot larger number of bacterial DNA bits. [6] But again, magnitudes matter. As I recently learned in a class here, MCB 148, bacterial genome sizes are much, much smaller, than human genomes, due to a necessity to conserve energy when reproducing. [7] Furthermore, bacterial genomes are pumped full of genes, that is, almost all bits of their DNA are used for coding some protein or another, while, our genomes have vast regions of bases thought to be “useless” (although we keep finding uses for them!)

Screen Shot 2017-06-01 at 7.06.05 AM.png
Figure 3: While the number is constantly being debated, the fact that bacteria have found a home in our body cannot be disputed. Also, growing this shape exactly on the petri dish must’ve taken a bit of skill! [8]
So after pondering the fact for a bit, it became readily apparent that the numbers, really, truly do matter. If you’ve been paying attention, you might’ve noticed that I haven’t calculated the % human DNA composition of the human body for you. Right now, I’m a bit busy (and probably a lot more lazy), but I thought examples like these really encapsulated the essence of biology, that is, that there still exists many open problems that I won’t have the answer to.

Ultimately, I’ve found myself really re-evaluating the importance of courses I thought were largely useless before, (i.e. history and english… Sorry professors!) but really in only the selfish way that it benefits what I enjoy studying most. So to those of you wondering where I’ve gone, I’m still here, still thinking up weird thoughts, and will be sticking around like the proverbial cholera on intestinal linings.

Your friend,

Joseph

p.s. Thanks to Leo Chen for this post idea, it came from a conversation probably a couple months back that resurfaced again today

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s