I inch my chair forward toward the table and earnestly peer over the paper my older sister Markita is writing on.

“To start you look at the first number, and then work your way down,” she explains. My brow furrows in concentration as she explains how to tackle the advanced math problems I have had trouble with in my fifth-grade class.

“Now, pretend this is how many cookies you have. If you had seven friends, how many whole cookies would they each get?” she asks. I consider the question thoughtfully.

“Two!” I say, beginning to now grasp not only the rote steps but also the concepts behind them.

“Good. And how many would be left over for you to eat?”

After working through a few more problems and developing a serious need for sugar, we rush upstairs to find our father, the designated Sunday afternoon ice cream scooper.

Today, as one of the newest assistant professors in the Department of Chemical and Biomolecular Engineering, my older sister, Markita Landry, is a teacher and mentor for all the undergraduates, graduate students, postdocs and visiting scholars that pass through her lab and her classroom. From experience I know that she takes her role as a mentor seriously, having served as my role model throughout my life.

I watched in elementary school as Markita devoured book after book in our living room, uninterested in helping me bargain with my mom for more TV time. In the winter months I held her hand firmly as she shuffled me across the ice-skating rink in the courtyard of our school in Canada, where we grew up.

When we visited family in Bolivia, she held my hand as we weaved in and out of the street markets in La Paz, pausing only to buy salteñas or to catch our breath when the high altitude left us winded. In high school, after our family moved to North Carolina, she left me awestruck when she joined the wrestling team, demonstrating in one fell swoop her drive, originality and, well, girl power.

College was where the first formal signs of the professor-to-be emerged. As a biochemistry major at the University of North Carolina at Chapel Hill, her intention was to go to medical school. Instead, she was charmed by one of her electives, modern physics.

“I had a great professor who showed us how abstract physics is relevant to real life,” Markita later told me. “I realized then that I wanted to use physics to understand the biological processes I was learning in my other classes.”

After tacking on a physics degree and disappointing our parents—who had warmed up to the idea of a medical doctor in the family—she joined the lab of Professor Brian Kuhlman, where she performed experiments to confirm the lab’s computational modeling of protein-protein binding interactions.

As a high schooler at the time, I spent weekends with her in the dorms, always welcome to spend the night and never made aware that I was perhaps spoiling a night or two out. I watched my sister navigate through college and learned not only about her classes, but also how to make the dining-hall lunch pass stretch into dinner and how to use this cool new website called Facebook.

Later, I saw her off to graduate school at the University of Illinois at Urbana-Champaign, where she earned her Ph.D. in chemical physics. I continued to visit, for weeks at a time, and often accompanied her into the lab of Yann Chemla—a former postdoc from the lab of Carlos Bustamante at UC Berkeley—to learn about their work studying protein-DNA interactions using optical tweezers to hold and manipulate biopolymers.

As one of the first graduate students in the Chemla group, Markita spent much of the early years setting up the lab. “There were a lot of boxes,” she recalls, laughing. The optical tweezers had to be adjusted to prevent them from damaging DNA, while other instruments had to be calibrated to understand their temperature sensitivity. Eventually she was able to get the equipment to cooperate.

“Once the Chemla lab was up and running, I tracked proteins as they translated DNA and found that they were monomers, not dimers,” she said. “This confirmed a proposed mechanism of protein movement along DNA. Being one of the first to join the Chemla lab gave me a good appreciation of the process of starting and running a lab. I enjoyed all aspects of it—grant writing, presenting and working with the other students—in addition to the experiments.”

Not satisfied with restricting her graduateschool experience to one technique, one research group or even one country, she found ways to expand and complement her work through collaborations. I heard how, as part of the NSF East Asia and Pacific Summer Institute, in the lab of Toshio Yanagida at Osaka University in Japan, she imaged proteins interacting with single DNA strands by using total internal reflection fluorescence (TIRF) microscopy.

“I made bridges out of DNA on micropedestals,” she explains. “This way I could watch proteins move along the DNA bridges.”

I later heard stories of how the German graduate students in the lab of Hermann Gaub at the Technical University in Munich taught her how to functionalize nanomaterials with polymers. After a stay of only one month, she could tune her fluorescence signals by changing the functionalization herself.

Markita would return to Germany to attend the 2010 Lindau Nobel Laureate Meeting, sharing the opportunity with hundreds of other young researchers to mix and mingle with 59 Nobelists. Her successes in graduate school motivated her to pursue a career in academia. Her graduate school experiences also motivated me to pursue a Ph.D., leading me to enroll in the Department of Chemical and Biomolecular Engineering at UC Berkeley. Neither of us would have guessed that the department would one day include both Landry sisters.

Markita next focused on her new postdoc appointment in the Department of Chemical Engineering at MIT. There, in the lab of Michael Strano, she used the tools she had learned from studying single-molecule biophysics in Illinois and Japan to build a near-infrared fluorescence microscope that could image the polymer-functionalized nanomaterials she had learned to synthesize in Germany. In doing so, she created sensors capable of detecting biologically relevant molecules at the short timescales and small length scales that are relevant for biological function.

Now at UC Berkeley, my sister and her research group are hoping to take her sensors one step further, to image at the single-molecule scale in vivo. One of Markita’s greatest interests is in detecting and studying elusive biomolecules such as dopamine, a neurotransmitter.

“It’s difficult to detect, let alone image, neurotransmitters in the brain. We specifically focus on molecules that don’t have molecular recognition elements and where optical detection is challenging, such as in the deep tissues of the brain.”

Working in collaboration with Linda Wilbrecht, who studies behavior and learning in mice in Berkeley’s Department of Psychology, Markita aims to directly image when and where key neurotransmitters are released in the brain, and how that process may be affected either by a subject’s environment or behavioral disorders.

Our parents and I are not the only ones who believe my sister’s research holds promise. Her preliminary results and tenacious hard work have so far earned her a 2015 Burroughs Wellcome Fund Career Award, as well as a 2016 Beckman Young Investigators Award.

And yet, even with the busy schedule of a new assistant professor, Markita still has found the time to go out tango dancing with me and to travel across Malaysia during winter break (even if it meant toting along her laptop to finish up some grant applications).

However, the most memorable moment for me came in May 2016, when as a member of the CBE faculty, my big sister hooded me as I was presented with my Ph.D. in chemical engineering—a fitting task for someone who has mentored me for over two decades. I can speak first-hand to the value of her guidance, and I can’t wait to see what remarkable ideas, projects and students emerge from her lab.