Chalk Talks

2012 Dec 06

Evolution of the Genetic code and the Ribosome

9:00am

Location: 

Biological Laboratories, 16 Divinity Ave., BL Room #1075, Cambridge, MA

Hyman Hartman (MIT-Dept. of Earth, Atmospheric & Planetary Sciences)

Messenger RNA is translated into Protein by the translational machinery of the cell, which includes twenty enzymes that attach the twenty amino acids to the transfer RNAs (tRNAs) with the correct anticodon. These enzymes are aptly called the Aminoacyl-tRNA synthetases. The machinery also includes the initiation and elongation factors and then there is the Ribosome, which is composed of a large subunit (LSU) and a small subunit (SSU). The ribosome has been crystallized and its three...

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2012 Nov 01

An early reducing atmosphere inferred from mantle noble gases

9:00am

Location: 

Biological Laboratories, 16 Divinity Ave., BL Room #1075, Cambridge, MA

Sujoy Mukhopadhyay (Dept. of Earth & Planetary Sciences)

The composition of the Earth’s early atmosphere is of great importance in understanding the nature of chemical reactions occurring on our planet’s surface. For example, an early reducing atmosphere has been shown to be significantly more conducive to prebiotic chemistry than an oxidized H2O-CO2 atmosphere. The composition of the earliest atmosphere is, however, a strong function of whether atmospheric gases were liberated from the Earth’s mantle or delivered via late accreting chondritic planetesimals...

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2012 Oct 04

A New Model for the Origin of the Earth and Moon

9:00am

Location: 

Biological Laboratories, 16 Divinity Ave., BL Room #1075, Cambridge, MA

Sarah Stewart (Dept. of Earth & Planetary Sciences)

In the standard model for planet formation, Earth accreted via a series of giant impacts and the terminal giant impact produced the Moon and fully melted the Earth. The Moon and Earth are identical in multiple isotope systems that show significant variations between most meteorite groups and planetary bodies. Thus, the simplest explanation for the isotopic similarity is that the Moon and Earth’s mantle have a common origin. In contrast, canonical giant impact simulations find that the lunar disk is...

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2013 Mar 07

The chemical mechanism of non-enzymatic RNA polymerization

9:00am

Location: 

Biological Laboratories, 16 Divinity Ave., BL Room #1075, Cambridge, MA

Craig Blain (GSAS-Biological & Biomedical Sciences Program/Szostak Lab)

In the earliest stages of the development of life, before the evolution of complex RNA or protein enzymes, the genetic information stored in nucleic acids had to be copied without the help of sophisticated catalysts. A common model for this process is the template-directed polymerization of imidazole-activated nucleotides from the 3’-end of a primer. Despite decades of studies on this system, the precise chemical mechanism of polymerization has not been determined. In particular, magnesium...

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2013 Apr 04

Constraining the global sulfur cycle at the enzymatic scale

9:00am

Location: 

Biological Laboratories, 16 Divinity Ave., BL Room #1075, Cambridge, MA

Wil Leavitt (Dept. of Earth & Planetary Sciences/Johnston Lab)

The sedimentary sulfur isotope record is an integrator of biochemical processes, the most quantitatively important of which is microbial sulfate reduction (MSR). Interpretations of the sedimentary sulfur isotope record rely largely on our understanding of the fractionation associated with MSR. This has been empirically determined by numerous cellular-scale studies [1, 2, 3]. Still, a mechanistic understanding for the controls on this fractionation has proven elusive. Moreover, metabolic...

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2013 May 02

A Possible Mechanism for Methane Outgassing in Water Planets

9:00am

Location: 

Biological Laboratories, 16 Divinity Ave., BL Room #1075, Cambridge, MA

Amit Levi (Harvard-Smithsonian Center for Astrophysics)

Planets with a substantial ice mass fraction, covering their entire surface, and lacking an H/He atmosphere are commonly referred to as water planets. These planets, first suggested as a Gedanken experiment by Kuchner (2003) and Leger et.al. (2004) based on the large variety among discovered extra-solar systems, have become an astronomical fact with the large number of low planetary mean densities as measured by the Kepler mission. Water planets appear to be relatively common, and being a novel type of planet...

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