Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Life in a Bottle Lecture Eleven, Feb. 10, 2003 Course Project • Topic of your choosing related to class. • Proposal (1-2 pages) Feb. 14, 2003. • Project background (3-5 pages) Mar. 28, 2003. • Project (10 pages) April 25. Pathfinder the Race to Mars • 60 min video on web site. • 1996 Mars Global • • • Surveyor lunched to orbit and map Mars. Also Mars Pathfinder with its small rover. These followed failed Mars Observer in 1993. See Manyrovers_full.jpg (note, this is a 7.4 MB image) The Doomsday Asteroid • 60 min Video • about impact of comet Shoemaker Levy 9 with Jupiter and present day threat from impacts. Keck Telescope infrared images of collision. Hubble Image of Impact Plum Impact site itself just out of site beyond rim Gamma Ray Bursts • The Nova program Death Stars discusses Gamma Ray bursts. These are the most energetic explosions since the Big Bang. They have now been detected billions of light years from Earth. Simulation of collapse of giant rotating star to produce two gamma ray jets. New Horizons Mission to Pluto The Kuiper belt: Frontier of Solar System Spacecraft will flyby Pluto and then on to a Kuiper belit object. See http://pluto.jhuapl.edu Origin of Life According to Michelangelo Origin of life according to Mel Brooks. Real Media clip of creation of life from Young Frankenstein The Chemistry of Life • Start with very simple chemicals such as CO2, H2O, N2, NH3. • Temperature and pressure allow liquid H2O. • Energy source: could be ultraviolet radiation from Sun, Lightening, Chemical reactions. • Somehow produce the building blocks of life. Amino Acids: Building Blocks of Life • Amino acids are chemical compounds with amine groups • (containing nitrogen, N) and weak acid groups (HO2C) that can be linked together to form long chains called proteins. Example: Amino acid Alanine H H N H C O C O Acid group H Amine group H C H H Chemistry 101: Note, 4 bonds for C, 3 bonds for N, 2 for O and 1 for H Two amino acids H N C H O C H Acid group N C O H C Amine group H C H H H C O H H O H H H H • The amine group of one amino acid can react with the acid group of another to produce a molecule of H2O and the joining of the two. These react to form H2O H O C N O H C H H H C C H H O O H C H H H N H N H C H C H H2O + O H C N Two amino acids H C O H C H H C O H H H H C H H One longer chain that still has an amine and an acid group Proteins are Made of Amino Acids • Amino acids have an amine group (N) and an • • • • • acid group (CO2H) Can bind amino acids together to produce long molecules called proteins. Proteins form the basis for life on Earth. Earth life uses proteins made from 20 different amino acids strung together in definite orders. Where did the amino acids come from? How were they put together in the correct order? Life made from 20 amino acids Glycine Valine Alanine Lysine Note, carbons at ends of lines and hydrogens are not shown Red is oxygen (acid) and blue is nitrogen (amine) group A Protein • To specify a unique protein you must specify which one • • • of the 20 amino acids occurs first, which amino acid occurs 2nd and so on. A protein may be thousands of amino acids long. To specify the exact molecule one needs a long string of thousands of numbers each of which goes from 1 to 20. For example, 5-19-20-1-5-7-8-8-15-20-20-1-1-1-… Example let 1 be Glycine, 2 be Alanie … So this protein has amino acid #5 then #19, #20 and so on for thousands of links in the long chain. The Left Hand of God • A given amino acid • • can come in two mirror image forms. Life on Earth only uses the left handed form. We don’t understand the origin of this chirality (Greek word for hand). Origin of Life • Where did the amino acids come from? • How is the information stored to specify the sequence for each complex protein? • How is the information acted on to synthesis the proteins? • How do the complex proteins function to form a living organism? Life is Old • Life arose about 3.8 • • billion years ago. Clear fossils in 3.5 billion year old rocks. Problem, few older rocks have survived. Great bombardment and very hostile conditions 4 billion years ago and earlier. Isotopes and Age of Life • A carbon atom has 6 electrons. • Carbon nuclei therefore have six protons. They • can also have either 6, 7 or 8 neutrons to make isotopes of carbon 12C, 13C or 14C. The superscript indicates the mass number A which is the sum of the number of neutrons plus protons. Isotopes have the same number of protons but different numbers of neutrons. Natural Carbon is: • 99% 12C and 1% 13C • 14C is radioactive with a half life of about 5000 • • years. Thus all primordial 14C has long since decayed. Most chemical reactions are the same for different isotopes and will not change the ratio of 12C to 13C. Reactions important for life work very slightly faster for 12C than for 13C because it is lighter and so moves faster. 13C is change in isotope ratio • 13C is very small change in ratio of 13C to 12C • • • • compared to the normal value of this ratio. Carbon in living material today is slightly depleted in 13C. Interesting evidence that carbon in 3.8 billion year old samples also show this slight depletion. Suggests that life is at least 3.8 billion years old. Note, we have no undisturbed rocks on earth older than about 3.5 billion years old. Origin of Amino Acids? • Amino acids can be made • • from simple inorganic chemicals such as CH4, NH3, H2O… But how was this done? Were the original amino acids extraterrestrial? Amino acids are found in some meteorites. Allende Meteorite Miller Experiment • Stanley Miller, a graduate • • student of Harold Urey, in 1953 placed H2O, H2, NH3, CH4 in a flask. He constantly boiled and recondensed the H2O and added an electrical discharge for energy. Spectacular results: produced lots of amino acids and other organic compounds. Miller Experiment • Miller thought he was simulating a • • thunderstorm on the primitive Earth. He put H2, NH3, CH4… in the exp. because these had just been seen (via spectroscopy) in the atmosphere of Jupiter. We now think early atmosphere was CO2 and had no free hydrogen. Without free hydrogen the experiment does not work and few amino acids are made. Jupiter Miller Experiment • Suggests that amino acids are easy to make under the right conditions and may be common through out the Universe. • Thus the building blocks of life may be common! • However, we don’t know where the correct conditions occurred. The lack of H2 on the early Earth appears to be a real problem. • Perhaps amino acids were made off the Earth in a site with free hydrogen. DNA the Memory of Life • How does life store the considerable information needed to specify a complex protein? • This information is encoded in molecules of DNA. • DNA is made from four base pairs: adenine, thymine, guanine, and cytosine on a double helix backbone. The Four Base Pairs in DNA • The molecule adenine • (a) always pairs with thymine (t) and guanine (g) pairs with cytosine (c). The information in DNA is stored in which of the four (a,c,g,t) occur at each position along the double helix. DNA • Double helix structure • Genetic code in order of • • the four bases (a,c,g,t) arranged along one of the helix strands. For example, start at the bottom with the strand starting to the left: a c t g atgggtactt Information in 2nd strand is the same. DNA can Replicate! • Double helix “unzips” and • • then new base pairs are added to each single stand to make two identical copies of the original DNA molecule. This allows cells to divide with full copies of the genetic code in each cell. The structure of DNA helps explain reproduction. DNA Codes for Proteins • DNA is not a protein and it is not made of amino • • • acids. DNA codes for the synthesis of proteins. Thus DNA stores the information needed to make a complex protein. Modern cells have complex machinery to read the DNA information and assemble amino acids to make proteins. How did early life do this before the complex machinery was evolved? For next time • Read chap. 4 of Jakosky about the earliest life and read “Vital Dust", pages 1-23 in course packet about origin of life. • Think about your course project. Proposal (1-2 pages) due Feb. 14, 2003.