Tag Archives: biophysics

7 Things To Know About Mitochondria: 2016 edition

Mitochondria: To most people, they’re little more than a ghostly memory fragment from middle school biology. However, these tiny “powerhouse(s) of the cell” are much more than they seem.

They’re actually the shape-shifting descendants of ancient bacteria that were eaten by a larger archaebacterium billions of years ago. . (If you want to know more about that theory, check out my recent Lateral magazine piece on the scientist who developed that theory.)  Mitochondria have complex relationships with other organelles, swim around in our neurons, and make up 1/3rd of the mass of heart cells.  In the past year, scientists have learned how to add and remove them with cellular surgeries and how to manipulate them directly.

Mitochondria live in every cell in your body and are essential for human life. As University of California post doc Samantha Lewis pointed out to me: “There’s mitochondrial involvement in almost every disease.” 

Yet, we rarely hear of or think about our cells’ powerhouses.

Here are seven facts you probably haven’t heard about mitochondria:

1:  Mitochondria are interconnected shape-shifters.

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[A bone cancer cell with stringy mitochondria highlighted in yellow. Photo by NICHD via Flickr & CC 2.0 License.] 

We say “Mitochondria is the powerhouse of the cell” as if mitochondria is a singular word, but actually it’s plural. (The singular of mitochondria is mitochondrion.)  However, in most cells mitochondria act as a collective, passing electrons and genetic information from mitochondrion to mitochondrion.

“They’re [descended from] bacteria that divide in a binary fashion,” explained UC Davis cell biologist and mitochondria specialist Jodi Nunnari. “During the course of evolution [the mitochondrial] genome has been greatly reduced. As a consequence of that and the fact that they were reproducing in a new environment, a few of those do mitochondrial fusion.” Mitochondria’s habit of merging sets them apart from all known bacteria. “Bacteria divide, but they don’t fuse,” Nunnari added.

In fact, mitochondria are so tightly connected that many scientists think of them as a membrane network rather than a series of jelly-bean shaped organelles.

Continue reading “7 Things To Know About Mitochondria: 2016 edition” »

Why DNA is like a phone cable (Recap of a Talk by Prof. Jacqueline Barton)

[Computer rendering of DNA. Via Caroline Davis2010 on Flickr & CC 2.0] 

The Talk:

“DNA-mediated Signaling with Metalloproteins”

In Plain English:

DNA can conduct electricity–like metal wire–and that helps the cell life

The Speaker:

Jacqueline Barton of Caltech

The Sponsor:

MIT Inorganic Chemistry (invited by the grad students)

What It Covered:

When Jacqueline Barton’s lab began publishing papers claiming that DNA can conduct electricity, many of her colleagues didn’t believe them. But in experiment after experiment, they kept finding that they could send small amounts of electricity–much lower than the amount that flows through your charger cord–from an electrode on one end of a DNA strand through to the other.

The exceptions were stretches of DNA with “missense mutations“, hiccups in the genetic code that violated the rule of “G” aligns with “C” and “A” aligns with “T”.

A,T, G, and C are biologists’ shorthand for four small molecular structures– adenine, thymine, guanine, and cytosine– that repeat over and over again along DNA’s backbone. It just so happens that a G-C pair takes up exactly the same amount of space and adds exactly the same amount of twist as an A-T pair.  Anything else–a misplaced guanine, a broken cytosine, or a chemical tag on thymine– throws the DNA’s twist out of whack. And apparently,  the missense mutations also blocked electrical currents’ flow through a tiny gap in the center of the DNA.  Mismatched base pairs or base pairs that were even slightly damaged blocked the electrons’ path. Continue reading “Why DNA is like a phone cable (Recap of a Talk by Prof. Jacqueline Barton)” »

5 Amazing Feats Performed by “Meta-Genes”

[Image via the NIH Image Gallery. Photo by Alex Ritter, Jennifer Lippincott Schwartz, and Gillian Griffiths. Full video, complete with narration here.] 

Under the Radar: A series of listicles about biology concepts you definitely won’t find in newspaper headlines.

#1: Be a Navigation App for Immune Cells

Natural killer cells, or “NK cells” are the human body’s best defense against cancer.  While other types of immune cells often ignore tumor cells, natural killer cells specialize in finding and destroying human cells that look either infected or like cancer mutants. In leukemia patients,  a higher number of active natural killer cells ups the patient’s chances for survival, so much so that  researchers are experimenting with transfusing NK cells into patients.

Just one problem there: Active natural killer cells die without a strong support network.

Dormant NK cells can survive in the bloodstream for a long time, but once activated, natural killers have to make a b-line for cells carrying a marker called IL-15 or die,  but until a study in Monday’s edtion of PNAS , no one knew how natural killers knew to look for IL-15. The study, led by Vanderbilt immunologist Eric Sebzda and grad student Whitney Rabacal, traced NK cells’ IL-15 homing ability back to a biochemical with the horrendous name “Kruppel-like Factor 2” (KLF2).

KLF2, oddly enough, also exerts a strong navigational influence on the immune system’s T-cells and B-cells.  Even though all three types of cells fall under the “white blood cell” umbrella, the notion that one protein could control navigation in all three is pretty weird.  Crawling and navigating are complex tasks, requiring coordination between dozens of genes. “[NK cell migration] is totally different from how t-cells and b-cells circulate,” Sebzda said.

Additionally, taking away KLF2 has distinctive effects on each type of cell: KLF2-less t-cells vacate the central body and crawl out to lab mice’s fingers and toes, KLF2-less b-cells all congregate at the spleen (which creates some serious problems for those lab mice), and KLF2-less natural killers end up dying alone.

So KLF2 could be super-useful for improving cancer immunotherapy. But why is KLF2 so versatile in the first place?

The answer lies in KLF2’s ability to bind to a certain recurring DNA base pair sequence, one that presumably earmarks the genes needed in each immune system navigation system, and it’s far from the only protein with such abilities…

Continue reading “5 Amazing Feats Performed by “Meta-Genes”” »

Bioelectric signals tell organisms when to grow limbs (among other things) – Recap of talk by Dr. Michael Levin

[This post is part of a series called “Brown Bag Lunch Reports” where I recap some of the academic talks given at college campuses in and around the city of Boston. Let me know what you think of the post format and what kinds of talks you think I should recap next!]

The Talk’s Title:

Manipulating natural bioelectric gradients to control growth and form in embryogenesis, regeneration, and cancer

In Plain English:

Changing the ways electric signals flow through living tissues alters the organisms’ growth in profound ways, including (but not limited to) the regeneration of complex organs like eyes and limbs.

The Speaker:

Michael Levin, Ph.d. of the Tufts Center for Regenerative Medicine and Developmental Biology

The Location:

Northeastern University’s Center for Interdisciplinary Research on Complex Systems

What it covered:

Dr. Michael Levin’s lab investigates a little-known (and if half of what he says is true, very underappreciated) topic in biology: the effect of variation in the electric charges of cells on morphological development. If that last sentence sounded like a random string of sciencey-sounding words from different disciplines, there’s a reason for that: Dr. Levin’s work draws heavily from both physics and molecular biology. Continue reading “Bioelectric signals tell organisms when to grow limbs (among other things) – Recap of talk by Dr. Michael Levin” »