Toxicodendron sp.

0 Comments
Poison ivy berries
Toxicodendron sp., judging by a range map here, probably T. rydbergii – poison ivy. As I was taking the picture, someone came by and announced, "Berries white, run in fright," which is pretty good advice. For a picture of poison ivy leaves with their characteristic mitten shape, see here. The leaves may be red in the fall; but they are not always red.

To see comments on this post click below:

“The song of the cell” by Siddhartha Mukherjee: review

0 Comments
Book cover

Joel Eissenberg is Professor of Biochemistry and Molecular Biology at Saint Louis University School of Medicine. He is the author of the recent PT article, How humans lost their tails.

As a college junior, I took a course in microbial genetics. The text was Gunter Stent’s Molecular Genetics. I map the beginning of my career as a geneticist to that course. Stent’s book is a history of the origins of molecular biology, and in retrospect, I believe it was the combination of the history and the science that beguiled me. This potent combination is on offer in Siddhartha Mukherjee’s The Song of the Cell: An Exploration of Medicine and the New Human. I generally avoid popular science books in my field, but this book was a gift from my daughter. I had read and enjoyed Mukherjee’s The Emperor of all Maladies, so I was hoping for something special. I was not disappointed.

The factual information about cells and their roles in tissues and organs, and in disease were well established by the time most of us learned it in school, we mostly learned it by rote. Mukherjee uses the history of scientific discoveries about cells to show us not only each discovery, but also the context in which it was made and the impact it had on thinking at the time. Indeed, the book is chock-a-block with historical anecdotes. Many of these discoveries were controversial at the time, like germ theory as the basis for putrefaction and for disease. The esteemed evolutionary biologist Ernst Mayr mocked Carl Woese’s proposal of Archea as a third kingdom of life; Mayr was wrong and Woese was vindicated. Even today, the origins of eukaryotic cells are still controversial.

Mukherjee is a marvelous storyteller. For example, he tells the story that when lipids were extracted from a carefully measured number of red blood cells and spread out on a surface, the area was twice that necessary to contain that number of cells, pointing to a lipid bilayer, rather than monolayer. He is very effective at explaining how discoveries emerge at the confluence of scientific disciplines; e.g., the marriage of microscopy and biochemistry to define the functions of various organelles.

How humans lost their tails

0 Comments
Cartoon depiction of two Alu elements in mirror-image orientation flanking an interval of chromosomal DNA (“Spacer”). See text for details.
Cartoon depiction of the two elements shown above, but folded to show pairing of the related sequences. Credit for both figures: Mitchell L Fullerton, "A Comparison of 100 Human Genes Using an Alu Element-Based Instability Model," PLOS ONE, DOI: 10.1371/journal.pone.0065188. Creative Commons Attribution 4.0 International License.

Joel Eissenberg is a professor of Biochemistry and Molecular Biology at Saint Louis University School of Medicine. His research interests include transcriptional control of gene expression and vesicle trafficking. He has had a lifelong fascination with genomics and with developmental biology.

In a recent Nature paper, Xia et al. offer a mechanistic explanation for tail-loss evolution in humans and anthropomorphous apes. It turns out that loss of a tail is caused by loss of a gene function among the tailless primates. And as the paper shows, this evolutionary transition was mediated by transposable elements, that is, repeated parasitic DNA fragments that are found in all living things.

Nannopterum auritum

0 Comments
Double-crested cormorant
Nannopterum auritum – double-crested cormorant, Wally Toevs Pond, Boulder, Colorado, March, 2024. The photographer writes: "Not my best picture ever, but it shows the double crests exceedingly well. According to All about Birds, the crests are seen on adults only during the breeding season, by which they presumably mean both sexes." He thanks Photonix, the god of photography, for enabling digital image processing.

To see comments on this post click below:

Leaf with dew drops

0 Comments

Photograph by Ken Phelps, a.k.a. Capt. Stormfield.

Photography Contest, Honorable Mention.

Leaf with dew drops
Morning dew on an unidentified leaf, Ganges, Saltspring Island, B.C. Canon 40D, 100 mm macro. Mr. Phelps writes: "Vancouver Island is temperate rainforest. Our property is mostly a sharp, rocky ridge with a couple micro-climates. Standard issue fir trees, ferns, etc. on the north side, and a bit more of a Southern Oregon feel on the top of the ridge, with some pines and lots of Arbutus. Very hot in summer with all the rock." He adds that since taking the photo some years ago, he has learned that the droplets might be due to transpiration rather than dew. He further adds parenthetically that Capt Stormfield is a "name adopted from Mark Twain's short story 'Extract from Captain Stormfield's Visit to Heaven.' Reading this at the age of 14 – despite the disapproval of the teacher at the [Seventh Day Adventist] church school I was attending – is my first recollection of the awakening skepticism that led me out of fundamentalism by my undergrad years."

To see comments on this post click below: