More Recent Comments

Showing posts with label Biochemistry. Show all posts
Showing posts with label Biochemistry. Show all posts

Friday, April 21, 2017

Thursday, April 20, 2017

Bill Martin is coming to town!!!

Contact me by email if you'd like to meet him on Sunday, April 30th.




The last molecular evolution exam: Question #6

How can alleles be fixed in a population by positive natural selection (i.e. adaptation) if the environment remains constant for thousands of years?

Question #1, Question #2, Question #3, Question #4, Question #5, Question #6


The last molecular evolution exam: Question #5

Many people believe that recombination evolved because it increases genetic variation in a population and this provided a selective advantage over species that didn’t have recombination. Do you agree with this explanation for the evolution of recombination? Why, or why not? What are the other possibilities?

Question #1, Question #2, Question #3, Question #4, Question #5, Question #6


The last molecular evolution exam: Question #4

More than 90% of our genome is transcribed when you add up all the transcripts from various cell types and various times of development (= pervasive transcription). Many biologists take this as evidence that most of the DNA in our genome is functional. What are the counter-arguments? Who do you believe and why?

Question #1, Question #2, Question #3, Question #4, Question #5, Question #6


The last molecular evolution exam: Question #3

The Three Domain Hypothesis has eukaryotes and archaea branching off from eubacteria. It shows eukaryotes more closely related to archaea than to eubacteria. However, many scientific studies indicate that a majority of our genes are more similar to eubacterial genes than to archaeal genes. How do you explain this apparent conflict?

Question #1, Question #2, Question #3, Question #4, Question #5, Question #6


The last molecular evolution exam: Question #2

The paper by Andrews et al. (2011) lists a number of common misconceptions held by their students. One of them is the idea that, “Evolution is a process that will never stop, even in the human species.” Why do they think this is a misconception? Do you agree?

Andrews, T.M., Kalinowski, S.T., and Leonard, M.J. (2011). “Are humans evolving?” A classroom discussion to change student misconceptions regarding natural selection. Evolution: Education and Outreach, 4:456-466. [doi: 10.1007/s12052-011-0343-4]
Question #1, Question #2, Question #3, Question #4, Question #5, Question #6


The last molecular evolution exam: Question #1

Eugene Koonin described his view of the proper null hypothesis for evolutionary questions. One of the examples he used concerns the evolution of recent gene duplications (Koonin, 2016 p.5). Describe how one possible fate of these genes relates to constructive neutral evolution. What are the other possible fates of these genes? Which one is most likely?

Koonin, E.V. (2016) Splendor and misery of adaptation, or the importance of neutral null for understanding evolution. BMC biology, 14:114 [doi: 10.1186/s12915-016-0338-2]

... in eukaryotes, duplicates of individual genes cannot be effectively eliminated by selection and thus often persist and diverge. The typical result is subfunctionalization, whereby the gene duplicates undergo differential mutational deterioration, losing subsets of ancestral functions. As a result, the evolving organisms become locked into maintaining the pair of paralogs. Subfunctionalization underlies a more general phenomenon, denoted constructive neutral evolution (CNE).

Question #1, Question #2, Question #3, Question #4, Question #5, Question #6


Saturday, April 08, 2017

Somatic cell mutation rate in humans

A few years ago, Tomasetti and Vogelstein (2015) published a paper where they noted a correlation between rates of cancer and the number of cell divisions. They concluded that a lot of cancers could be attributed to bad luck. This conclusion didn't sit well with most people for two reasons. (1) There are many well-known environmental effects that increase cancer rates (e.g. smoking, radiation), and (2) there's a widespread belief that you can significantly reduce your chances of getting cancer by "healthy living" (whatever that is). The first objection is based on solid scientific evidence but the second one is not as scientific.

Some of the objections to the original Tomasetti and Vogelstein paper were based on the mathematical models they used to reach their conclusions. The authors have now followed up on their original study with more data. The paper appears in the March 24, 2017 issue of Science (Tomasetti and Vogelstein, 2017). If you're interested in the debate over "bad luck" you should read the accompanying review by Nowak and Waclaw (2017). They conclude that the math is sound and many cancer-causing mutations are, in fact, due to chance mutations in somatic cells. They point out something that should be obvious but bears repeating.

Wednesday, February 22, 2017

Sloppiness in translation initiation

There are two competing worldviews in the fields of biochemistry and molecular biology. The distinction was captured a few years ago by Laurence Hurst commenting on pervasive transcription when he said, "So there are two models; one, the world is messy and we're forever making transcripts we don't want. Or two, the genome is like the most exquisitely designed Swiss watch and we don't understand its working. We don't know the answer—which is what makes genomics so interesting." (Hopkins, 2009).

I refer to these two world views as the Swiss watch analogy and the Rube Goldberg analogy.

The distinction is important because, depending on your worldview, you will interpret things very differently. We see it in the debate over junk DNA where those in the Swiss watch category have trouble accepting that we could have a genome full of junk. Those in the Rube Goldberg category (I am one) tend to dismiss a lot of data as just noise or sloppiness.

Friday, February 17, 2017

Did Rosalind Franklin produce the first X-ray diffraction images of DNA?

There's an interesting video of ten famous women scientists at Interesting S_Word: [Top 10 Female Scientists of History]. The image of Rosalind Franklin caught my eye (see right).


Perhaps I'm nitpicking but fake news is all the rage these days so I think we'd better be extra careful to present real facts rather than alternative facts. In that spirit, I'll mention two things.

Friday, February 03, 2017

Why is life the way it is?

Nick Lane is very good at explaining complex biology and biochemistry. He is the winner of the Royal Society's Michael Faraday Prize for 2016. Here's his lecture. It's worth watching if you want to understand the latest informed (naturalistic) speculations on the origin of life.




Trying to educate a creationist (Otangelo Grasso)

Otangelo Grasso is a creationist who's convinced he can learn to understand biochemistry by reading what's on the internet and copy-pasting it into his website. He then takes that limited knowledge and concludes that evolution is impossible. He often poses "gotcha" questions based on his flawed understanding.

His behavior isn't very different from most other creationists who suffer from Dunning-Kruger Disease but he happens to be someone who I thought could be educated.

I was wrong.

Over the years I've tried to correct a number of errors he's made so we could have an intelligent discussion about evolution. You can't have such a discussion if one side ignores facts and refuses to learn. Here's an example of a previous attempt: Fun and games with Otangelo Grasso about photosynthesis. Here's a post from yesterday showing that I wasted my time: Otangelo Grasso on photosynthesi.

Sunday, January 29, 2017

The evolution of the citric acid cycle

I just realized that I don't have a post devoted to the evolution of the citric acid cycle. This need to be remedied since I often talk about it. It's a good example of how an apparently irreducibly complex pathway can arise by evolution. It's also a good example to get students to think outside of the box. Undergraduate biochemistry courses usually concentrate on human physiology and too often students transfer that bias to all other species. They assume that what happens in humans is what happens in plants, fungi, protozoa, and bacteria.1

Here's what the standard citric acid cycle looks like (Moran et al., 2011 p. 393).

Saturday, January 07, 2017

What the heck is epigenetics?

"Epigenetics" is the (relatively) new buzzword. Old-fashioned genetics is boring so if you want to convince people (and grant agencies) that you're on the frontlines of research you have to say you're working on epigenetics. Even better, you can tell them that you are on the verge of overthrowing Darwinism and bringing back Jean-Baptiste Lamarck.

But you need to be careful if you adopt this strategy. Don't let anyone pin you down by defining "epigenetics." It's best to leave it as ambiguous as possible so you can adopt the Humpty-Dumpty strategy.1 Sarah C.P. Williams made that mistake a few years ago and incurred the wrath of Mark Ptashne [Core Misconcept: Epigenetics].

Tuesday, January 03, 2017

The exit exam for biochemistry and molecular biology students

I'm a big fan of teaching fundamental concepts and principles and a big fan of teaching critical thinking. I think the most effective way of accomplishing these objectives is some form of student-centered learning. As I near the end of my teaching career, I wonder how we can tell if we succeed? It should be relatively easy to develop an exit exam for our biochemistry/molecular biology students to see if they grasp the basic concepts and can demonstrate an ability to think critically.

Here are some of the questions we could have on that exam. Each one requires a short answer with an explanation. The explanation doesn't have to be detailed or full of facts, just the basic idea. Students are graded on their ability to think critically about the answers. Many of the questions don't have a simple answer. Can you think of any other questions?

Tuesday, December 13, 2016

The proteome complexity myth

A reader pointed me to the ThermoFisher Scientific website. ThermoFisher Scientific is a major supply of scientific equipment and supplies. They created their life sciences wesite to help inform their customers and sell more products. The page I'm interested in is: Overview of Post-Translational Modifications (PTMs). It begins with,

Within the last few decades, scientists have discovered that the human proteome is vastly more complex than the human genome. While it is estimated that the human genome comprises between 20,000 and 25,000 genes (1), the total number of proteins in the human proteome is estimated at over 1 million (2). These estimations demonstrate that single genes encode multiple proteins. Genomic recombination, transcription initiation at alternative promoters, differential transcription termination, and alternative splicing of the transcript are mechanisms that generate different mRNA transcripts from a single gene (3).

The increase in complexity from the level of the genome to the proteome is further facilitated by protein post-translational modifications (PTMs). PTMs are chemical modifications that play a key role in functional proteomics, because they regulate activity, localization and interaction with other cellular molecules such as proteins, nucleic acids, lipids, and cofactors.

Tuesday, December 06, 2016

How many proteins in the human proteome?

Humans have about 25,000 genes. About 20,000 of these genes are protein-coding genes.1 That means, of course, that humans make at least 20,000 proteins. Not all of them are different since the number of protein-coding genes includes many duplicated genes and gene families. We would like to know how many different proteins there are in the human proteome.

The latest issue of Science contains an insert with a chart of the human proteome produced by The Human Protein Atlas. Publication was timed to correspond with release of a new version of the Cell Atlas at the American Society of Cell Biology meeting in San Francisco. The Cell Atlas maps the location of about 12,000 proteins in various tissues and organs. Mapping is done primarily by looking at whether or not a gene is transcribed in a given tissue.

A total of 7367 genes (60%) are expressed in all tissues. These "housekeeping" genes correspond to the major metabolic pathways and the gene expression pathway (e.g. RNA polymerase subunits, ribosomal proteins, DNA replication proteins). Most of the remaining genes are tissue-specific or developmentally specific.

Tuesday, August 23, 2016

Splice variants of the human triose phosphate isomerase gene: is alternative splicing real?

Triose phosphate isomerase (TIM) is one of the enzymes in the gluconeogenesis pathway leading to the synthesis of glucose from simple precursors. It also plays a role in the degradation of glucose (glycolysis). The enzyme catalyzes the following reaction ....


Triose phosphate isomerase is found in almost all species. The structure and sequence of the enzyme is well-conserved. It is a classic β-barrel enzyme that usually forms a dimer. The overall structure of a single subunit is classic example of an αβ-barrel known as a TIM-barrel in reference to this enzyme.

To the best of my knowledge, no significant variants of this enzyme due to alternative promoters, alternative splicing, or proteolytic cleavage are known.1 The enzyme has been actively studied in biochemistry laboratories for at least eighty years.

Saturday, July 30, 2016

The most important thing about nature according to Bill Martin

My friend and colleague, Alex Palazzo, alerted me to an interview of Bill Martin published in the July 11, 2016 issue of Current Biology [Bill Martin]. I loved all his answers—Bill Martin is one of my scientific heroes—but his answer to the last question was particularly insightful. The question was, "What’s the single most important thing that you have come to realize about nature?"

His answer was ....
Life is an exergonic chemical reaction. It’s the energy releasing redox reaction at the core of metabolism that makes life run, and throughout all of life’s history it is one and the same reaction that has been running in uninterrupted continuity from life’s onset. Everything else is secondary, manifestations of what is possible when the energy is harnessed to make genes that pass the torch.
I'm a biochemist so you might think I'm a little bit biased but let me tell you why this answer is so important.