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Wednesday, October 09, 2024

Nobel Laureate: Aziz Sancar


The Nobel Prize in Chemistry 2015.

“for mechanistic studies of DNA repair”



Aziz Sancar won the 2015 Nobel Prize in Chemistry for his contributions to the study of DNA repair.

Sancar was born in Turkey in 1946 and got his MD degree from the Faculty of Medicine of Istanbul University. He then went on to get a Ph.D. with Claud S. Rupert at the University of Texas at Dallas in 1977. The Rupert lab worked on DNA repair and Sancar's thesis topic was the photoreactivating enzyme in E. coli. The photoreactivating enzyme was an enzyme that repaired DNA damage.

Sancar eventually secured a position at the University of North Carolina, Chapel Hill where he worked on excision repair and on photoreactivation. He is best known for his study of the mechanism of photolyase, the enzyme that repairs thymine dimers. [see Monday's Molecule #242] Photolyases are present in bacteria, protozoa, fungi, plants, and most animals. The gene for photolyase has been lost in placental mammals.

The information on the Nobel Prize website describes the career of Aziz Sancar.

THEME:
Nobel Laureates

Aziz Sancar’s fascination with life’s molecules developed while he was studying for a medical degree in Istanbul. After graduating, he worked for a few years as phycisian in the Turkish countryside, but in 1973 he decided to study biochemistry. His interest was piqued by one phenomenon in particular: when bacteria are exposed to deadly doses of UV radiation, they can suddenly recover if they are illuminated with visible blue light. Sancar was curious about this almost magical effect; how did it function chemically?

Claud Rupert, an American, had studied this phenomenon and Aziz Sancar joined his laboratory at the University of Texas in Dallas, USA. In 1976, using that time’s blunt tools for molecular biology, he succeeded in cloning the gene for the enzyme that repairs UV-damaged DNA, photolyase, and also in getting bacteria to over-produce the enzyme. This work became a doctoral dissertation, but people were hardly impressed; three applications for postdoc positions resulted in as many rejections. His studies of photolyase had to be shelved. In order to continue working on DNA repair, Aziz Sancar took up a position as laboratory technician at the Yale University School of Medicine, a leading institution in the field. Here he started the work that would eventually result in the Nobel Prize in Chemistry.

By then it was clear that bacteria have two systems for repairing UV damage: in addition to light-dependent photolyase, a second system that functions in the dark had been discovered. Aziz Sancar’s new colleagues at Yale had studied this dark system since the mid-1960s, using three UV-sensitive strains of bacteria that carried three different genetic mutations: uvrA, uvrB and uvrC.

As in his previous studies of photolyase, Sancar began investigating the molecular machinery of the dark system. Within a few years he had managed to identify, isolate and characterise the enzymes coded by the genes uvrA, uvrB and uvrC. In ground-breaking in vitro experiments he showed that these enzymes can identify a UV-damage, then making two incisions in the DNA strand, one on each side of the damaged part. A fragment of 12-13 nucleotides, including the injury, is then removed.

Aziz Sancar’s ability to generate knowledge about the molecular details of the process changed the entire research field. He published his findings in 1983. His achievements led to an offer of an associate professorship in biochemistry at the University of North Carolina at Chapel Hill. There, and with the same precision, he mapped the next stages of nucleotide excision repair. In parallel with other researchers, including Tomas Lindahl, Sancar investigated nucleotide excision repair in humans. The molecular machinery that excises UV damage from human DNA is more complex than its bacterial counterpart but, in chemical terms, nucleotide excision repair functions similarly in all organisms.

So, what happened to Sancar’s initial interest in photolyase? Well, he eventually returned to this enzyme, uncovering the mechanism responsible for reviving the bacteria. In addition, he helped to demonstrate that a human equivalent to photolyase helps us set the circadian clock.



The images of the Nobel Prize medals are registered trademarks of the Nobel Foundation (© The Nobel Foundation). They are used here, with permission, for educational purposes only.

Monday, October 07, 2024

Monday's Molecule #242

It's been a while since the last Monday's Molecule on May 19, 2014 but I think it's time to revive that tradition. I'll show you a molecule and you have to guess what it is without searching the internet. In other words, you have to recognize it immediately or it doesn't count. Email your answer to me at: Monday's Molecule #242. The first one with the correct answer wins. I will only post the names of winners to avoid embarrassment. The winner will be treated to a free coffee and donut at Tim Hortons if you are ever in Toronto or Mississauga (Ontario, Canada).1

There could be two winners. If the first correct answer isn't from an undergraduate student then I'll select a second winner from those undergraduates who post the correct answer. You will need to identify yourself as an undergraduate in order to win. (Put "undergraduate" at the bottom of your email message.)

Today's molecule (right) looks very complicated but I'm not going to ask you to give me a complete chemical name. The simple common name will do but you have to briefly explain it's biological significance and why it's always discussed in biochemistry textbooks.

In order to win you must post your correct name. Anonymous and pseudoanonymous commenters can't win.

Comments are closed for at least 24 hours.

UPDATE: The winner is Elie Huvier who pointed out that the molecule is a thymine dimer with a cyclobutane ring. Thymine dimers are mutations caused by ultraviolet light, which causes photodimerization of adjacent stacked pyrimidines in DNA. Elie Huvier was the first one to identify the molecule and describe its significance.

Winners

#145, Oct. 17, 2011: Bill Chaney, Roger Fan
#146, Oct. 24, 2011: DK
#147, Oct. 31, 2011: Joseph C. Somody
#148, Nov. 7, 2011: Jason Oakley
#149, Nov. 15, 2011: Thomas Ferraro, Vipulan Vigneswaran
#150, Nov. 21, 2011: Vipulan Vigneswaran (honorary mention to Raul A. Félix de Sousa)
#151, Nov. 28, 2011: Philip Rodger
#152, Dec. 5, 2011: 凌嘉誠 (Alex Ling)
#153, Dec. 12, 2011: Bill Chaney
#154, Dec. 19, 2011: Joseph C. Somody
#155, Jan. 9, 2012: Dima Klenchin
#156, Jan. 23, 2012: David Schuller
#157, Jan. 30, 2012: Peter Monaghan
#158, Feb. 7, 2012: Thomas Ferraro, Charles Motraghi
#159, Feb. 13, 2012: Joseph C. Somody
#160, March 5, 2012: Albi Celaj
#161, March 12, 2012: Bill Chaney, Raul A. Félix de Sousa
#162, March 19, 2012: no winner
#163, March 26, 2012: John Runnels, Raul A. Félix de Sousa
#164, April 2, 2012: Sean Ridout
#165, April 9, 2012: no winner
#166, April 16, 2012: Raul A. Félix de Sousa
#167, April 23, 2012: Dima Klenchin, Deena Allan
#168, April 30, 2012: Sean Ridout
#169, May 7, 2012: Matt McFarlane
#170, May 14, 2012: no winner
#171, May 21, 2012: no winner
#172, May 29, 2012: Mike Hamilton, Dmitri Tchigvintsev
#173, June 4, 2012: Bill Chaney, Matt McFarlane
#174, June 18, 2012: Raul A. Félix de Sousa
#175, June 25, 2012: Raul A. Félix de Sousa
#176, July 2, 2012: Raul A. Félix de Sousa
#177, July 16, 2012: Sean Ridout, William Grecia
#178, July 23, 2012: Raul A. Félix de Sousa
#179, July 30, 2012: Bill Chaney and Raul A. Félix de Sousa
#180, Aug. 7, 2012: Raul A. Félix de Sousa
#181, Aug. 13, 2012: Matt McFarlane
#182, Aug. 20, 2012: Stephen Spiro
#183, Aug. 27, 2012: Raul A. Félix de Sousa
#184, Sept. 3, 2012: Matt McFarlane
#185, Sept. 10, 2012: Matt Talarico
#186, Sept. 17, 2012: no winner
#187, Sept. 24, 2012: Mikkel Rasmussen
#188, Oct. 1, 2012: John Runnels
#189, Oct. 8, 2012: Raúl Mancera
#190, Oct. 15, 2012: Raul A. Félix de Sousa
#191, Oct. 22, 2012: Mikkel Rasmussen
#192, Nov. 12, 2012: Seth Kasowitz, Bill Gunn
#193, Nov. 19, 2012: Michael Rasmussen
#194, Dec. 4, 2012: Paul Clapham, Jacob Toth
#195, Dec. 10, 2012: Jacob Toth
#196, Dec. 17, 2012: Bill Chaney, Dima Klenchin, Bill Gunn
#197, Jan. 14, 2013: Evey Salara
#198, Jan. 21, 2013: Piotr Gasiorowski
#199, March 11, 2013: Bill Gunn, River Jiang
#200, March 18, 2013: Bill Gunn
#201, April 8, 2013: Michael Florea
#202, April 15, 2013: no winner
#203, April 29, 2013: Anders Ernberg
#204, May 6, 2013: Alex Ling, Michael Florea
#205, May 13, 2013: Bill Chaney
#206, June 24, 2013: Michael Florea
#207, July 2, 2013: Matt McFarlane
#208, July 8, 2013: no winner
#209, July 15, 2013: Rosie Redfield, Thuc Quyen Huynh
#210, July 22, 2013: Jacob Toth
#211, July 29, 2013: Alex Ling, Matt McFarlane
#212, August 5, 2013: Brian Shewchuk
#213, Sept. 2, 2013: no winner
#214, Sept. 9, 2013: Bill Chaney
#215, Sept. 16, 2013: Zhimeng Yu
#216, Sept. 23, 2013: Mark Sturtevant, Jacob Toth
#217, Sept. 30, 2013: Susan Heaphy
#218, Oct. 7, 2013: Piotr Gasiorowski, Jacob Troth
#219, Oct. 14, 2013: Jean-Marc Neuhaus
#220, Oct. 21, 2013: Jean-Marc Neuhaus
#221, Oct. 28, 2013: Zhimeng Yu
#222, Nov. 10, 2013: Caroline Josefsson, Andrew Wallace
#223, Nov. 18, 2013: Dean Bruce, Ariel Gershon
#224, Nov. 25, 2013: Jon Nuelle, Ariel Gershon
#225, Dec. 2, 2013: Jean-Marc Neuhaus
#226, Dec. 9, 2013: Bill Gunn
#227, Dec. 16, 2013: Piotr Gasiorowski
#228, Jan. 13, 2014: Tom Mueller
#229, Jan. 20, 2014: Tommy Stuleanu
#230, Jan. 27, 2014: Bill Gunn, Ariel Gershon
#231; March 3, 2014: Keith Conover, Nevraj Kejiou
#232, March 10, 2014: Philip Johnson
#233, March 17, 2014: Jean-Marc Neuhaus
#234, March 24, 2014: Frank Schmidt, Raul Félix de Sousa
#235, March 31, 2014: Jon Binkley
#236, April 7, 2014: no winner
#237, April 21, 2014: Dean Bruce
#238, April 28, 2014: Dean Bruce
#239, May 5, 2014: Piotr Gąsiorowski
#240, May 12, 2014: James Wagstaff
#241, May 19, 2014: no winner
#242, Oct. 7, 2024: Elie Huvier

1. I still owe some previous winners. If you are one of them, then you should email me to set up a time and place.

Thursday, October 03, 2024

Intelligent Design Creationists made up a fake march of progress illustration

Everyone is familiar with the typical March of Progress figures that are often used to illustrate evolution. However, most people don't know that evolutionary biologists object to that depiction of evolution because it seriously misrepresents the reality of human evolution.

Stephen Jay Gould has been one of the most vocal opponents of such icons because they imply a sense of direct linear progress from some primitive ancestor to a modern species when, in fact, the actual evolution involves branching trees with multiple lineages, most of which have gone extinct. In one of his most famous essays, Life's Little Joke (Gould, 1987, 1991), Gould explains why the evolution of horses is falsely depicted as a march of progress.

Tuesday, October 01, 2024

Jonathan Wells (1942 - 2024)

Johnathan Wells died recently. He was a well-known Intelligent Design Creationist and that's why Evolution News (sic) is eulogizing him by posting multiple tributes and excerpts from his books and essays.

I think it's only fair to post links to my efforts to demonstrate the serious flaws in his arguments. I'm particularly proud of the series of articles I wrote when he published his book The Myth of Junk DNA. I went through every chapter and analyzed his arguments against junk DNA. It won't surprise anyone to learn that I found those arguments lacking in substance and in some cases I discovered that Wells had misrepresented the science.

Here are my posts.

Jonathan Wells never responded directly to my criticism but he did respond to a comment that Paul McBride made on one of his blog posts. Paul asked him why he didn't respond to my post and here's what Wells said,

Oh, one last thing: “paulmc” referred to an online review of my book by University of Toronto professor Larry Moran—a review that “paulmc” called both extensive and thorough. Well, saturation bombing is extensive and thorough, too. Although “paulmc” admitted to not having read more than the Preface to The Myth of Junk DNA, I have read Mr. Moran’s review, which is so driven by confused thinking and malicious misrepresentations of my work—not to mention personal insults—that addressing it would be like trying to reason with a lynch mob.

This is typical of the attitude of most Intelligent Design Creationists. They are happy to publish lengthy books denegrating science and scientists but couldn't be bothered responding to criticism.

Here's are some other post of mine where I demonstrate the flawed thinking of Jonathan Wells.