Search for Life in the Universe Chapter 5 The Nature of Life on Earth (Part 2)
Announcement <ul><li>Midterm 2  is postponed until March 13 </li></ul><ul><li>Midterm 2 covers  Chapters 4-6 </li></ul><ul...
Outline <ul><li>Metabolism </li></ul><ul><ul><li>Basic Metabolic Needs </li></ul></ul><ul><ul><li>Carbon and Energy Source...
Basic Metabolic Needs <ul><li>Metabolism : chemical reactions within living organisms </li></ul><ul><li>Cell: Chemical rea...
 
Carbon and Energy Sources <ul><li>Carbon: </li></ul><ul><ul><li>Heterotroph : eat other organisms </li></ul></ul><ul><ul><...
Metabolism and Cells <ul><li>Metabolism : </li></ul><ul><ul><li>Four forms of metabolism defined by: </li></ul></ul><ul><u...
Importance of Water <ul><li>Importance: </li></ul><ul><ul><li>Contact : organic chemicals float in the cell and find each ...
Deoxyribose Nucleic Acid (DNA) <ul><li>Structure: </li></ul><ul><ul><li>Double helix of nucleotides: like two intertwined ...
 
DNA Replication <ul><li>Steps: </li></ul><ul><ul><li>Complete double helix </li></ul></ul><ul><ul><li>Strands separate int...
 
Genes, Genomes, & Genetic Code <ul><li>Gene : </li></ul><ul><ul><li>A sequence of DNA bases    instructions for a  single...
 
Ribonucleic Acid (RNA) <ul><li>Implementation  of the genetic code: </li></ul><ul><ul><li>Many  enzymes  involved </li></u...
Mutations and Evolution <ul><li>DNA is the mechanism for Darwin’s theory of evolution </li></ul><ul><li>DNA replication is...
Will Life Elsewhere Use DNA? <ul><li>Heredity and evolution are essential </li></ul><ul><li>DNA does the job on Earth toda...
Extremophiles <ul><li>Volcanic vents : </li></ul><ul><ul><li>Water temperature reaches 400  C (750  F), possible because...
 
 
 
 
Implications for Extraterrestrial Life <ul><li>Oxygen for eukarya on Earth for only ~10% of its life </li></ul><ul><li>Wha...
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Ch 5b

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Ch 5b

  1. 1. Search for Life in the Universe Chapter 5 The Nature of Life on Earth (Part 2)
  2. 2. Announcement <ul><li>Midterm 2 is postponed until March 13 </li></ul><ul><li>Midterm 2 covers Chapters 4-6 </li></ul><ul><li>The lecture on March 8 will cover Chapter 7 </li></ul><ul><li>Chapter 7 is not included in Midterm 2 (it will be included in Midterm 3) </li></ul>
  3. 3. Outline <ul><li>Metabolism </li></ul><ul><ul><li>Basic Metabolic Needs </li></ul></ul><ul><ul><li>Carbon and Energy Sources </li></ul></ul><ul><ul><li>Metabolism and Cells </li></ul></ul><ul><ul><li>Importance of Water </li></ul></ul><ul><li>DNA and Heredity </li></ul><ul><ul><li>Deoxyribose Nucleic Acid (DNA) </li></ul></ul><ul><ul><li>DNA Replication </li></ul></ul><ul><ul><li>Genes, Genomes, & Genetic Code </li></ul></ul><ul><ul><li>Ribonucleic Acid (RNA) </li></ul></ul><ul><ul><li>Mutations and Evolution </li></ul></ul><ul><ul><li>Will Life Elsewhere Use DNA? </li></ul></ul><ul><li>Life at the Extremes </li></ul><ul><ul><li>Extremophiles </li></ul></ul><ul><ul><li>Implications for Extraterrestrial Life </li></ul></ul>
  4. 4. Basic Metabolic Needs <ul><li>Metabolism : chemical reactions within living organisms </li></ul><ul><li>Cell: Chemical reactions much faster than in the open </li></ul><ul><ul><li>Collects the raw materials for the chemical reactions </li></ul></ul><ul><ul><li>Provides the energy for the reactions </li></ul></ul><ul><ul><li>Provides enzymes to catalyze the reactions </li></ul></ul><ul><ul><li>Instructions for enzymes encoded in DNA </li></ul></ul><ul><li>Adenosine triphosphate (ATP) and Diphosphate (ADP): </li></ul><ul><ul><li>ATP  endothermic reaction  ADP  exothermic reaction  ATP </li></ul></ul><ul><ul><li>Every living organism uses ATP </li></ul></ul><ul><ul><li>Other molecules would be equally effective </li></ul></ul><ul><ul><li>Unique use of ATP points to a single origin of life </li></ul></ul>
  5. 6. Carbon and Energy Sources <ul><li>Carbon: </li></ul><ul><ul><li>Heterotroph : eat other organisms </li></ul></ul><ul><ul><li>Autotroph : self-feeding by converting atmospheric CO 2 </li></ul></ul><ul><li>Energy: </li></ul><ul><ul><li>Photoautotrophs (plants): photosynthesis: CO 2 + H 2 O + sunlight  sugar </li></ul></ul><ul><ul><li>Photoheterotrophs (rare prokaryotes): carbon from food but make ATP using sunlight </li></ul></ul><ul><ul><li>Chemoheterotrophs (animals): energy from food </li></ul></ul><ul><ul><li>Chemoautotrophs (extreme prokaryotes): energy from chemicals and not sunlight </li></ul></ul>
  6. 7. Metabolism and Cells <ul><li>Metabolism : </li></ul><ul><ul><li>Four forms of metabolism defined by: </li></ul></ul><ul><ul><ul><li>Sources of carbon (direct or indirect) </li></ul></ul></ul><ul><ul><ul><li>Sources of energy (light or chemical) </li></ul></ul></ul><ul><ul><li>The four forms of metabolism are quite general and should apply to life anywhere </li></ul></ul><ul><li>Cells : </li></ul><ul><ul><li>Needed environment for metabolism at acceptable rate </li></ul></ul><ul><li>Origin of Life (on Earth and elsewhere): </li></ul><ul><ul><li>Look for cells as sites of metabolism </li></ul></ul>
  7. 8. Importance of Water <ul><li>Importance: </li></ul><ul><ul><li>Contact : organic chemicals float in the cell and find each other </li></ul></ul><ul><ul><li>Transportation : bring chemicals in and out of cells </li></ul></ul><ul><ul><li>Participant in reactions: </li></ul></ul><ul><ul><ul><li>ATP </li></ul></ul></ul><ul><ul><ul><li>Photosynthesis </li></ul></ul></ul><ul><li>Necessity: </li></ul><ul><ul><li>Life on Earth : all use water </li></ul></ul><ul><ul><li>Dormant without water: for a limited time only </li></ul></ul><ul><ul><li>Elsewhere : need a liquid </li></ul></ul><ul><ul><li>What are the alternatives ? </li></ul></ul>
  8. 9. Deoxyribose Nucleic Acid (DNA) <ul><li>Structure: </li></ul><ul><ul><li>Double helix of nucleotides: like two intertwined Slinky toys </li></ul></ul><ul><li>Composition: </li></ul><ul><ul><li>Deoxyribose (sugar) </li></ul></ul><ul><ul><li>A phosphate group, linked to the deoxyribose of the next nucleotide </li></ul></ul><ul><ul><li>One of four bases, which determine the genetic code </li></ul></ul><ul><li>Four bases: </li></ul><ul><ul><li>Adenine (A): A  T </li></ul></ul><ul><ul><li>Guanine (G): G  C </li></ul></ul><ul><ul><li>Thymine (T): T  A </li></ul></ul><ul><ul><li>Cytosine (C): C  G </li></ul></ul><ul><ul><li>Pairing forced by chemical shapes </li></ul></ul>
  9. 11. DNA Replication <ul><li>Steps: </li></ul><ul><ul><li>Complete double helix </li></ul></ul><ul><ul><li>Strands separate into 2 helices </li></ul></ul><ul><ul><li>Free floating bases join open strands </li></ul></ul><ul><ul><li>Fill in deoxyribose and a phosphate group </li></ul></ul><ul><ul><li>Two identical copies of the DNA in the cell </li></ul></ul><ul><ul><li>Cell division: one copy to each daughter cell </li></ul></ul><ul><li>Complexity: </li></ul><ul><ul><li>Enzymes : a dozen or more needed </li></ul></ul><ul><ul><li>Heredity : ensured by exact copying, but </li></ul></ul><ul><ul><li>Errors : occur occasionally  evolution </li></ul></ul><ul><ul><li>Origin of Life: need simpler mechanism (RNA?) </li></ul></ul>
  10. 13. Genes, Genomes, & Genetic Code <ul><li>Gene : </li></ul><ul><ul><li>A sequence of DNA bases  instructions for a single function </li></ul></ul><ul><ul><li>Basic unit of heredity </li></ul></ul><ul><li>Genome : </li></ul><ul><ul><li>Complete sequence of DNA : contains all genes </li></ul></ul><ul><ul><li>Human genome: </li></ul></ul><ul><ul><ul><li>~3 billion bases </li></ul></ul></ul><ul><ul><ul><li>20,000  25,000 genes </li></ul></ul></ul><ul><li>Genetic code : </li></ul><ul><ul><li>Rules for reading DNA </li></ul></ul><ul><ul><li>Genetic words : 3 bases in a row </li></ul></ul><ul><ul><li>Total number of words: 4 3 = 4 x 4 x 4 = 64 </li></ul></ul><ul><ul><li>Redundancy : only 20 amino acids used to make proteins </li></ul></ul><ul><ul><li>Only first 2 bases matter in most cases  Originally 2-base words? </li></ul></ul>
  11. 15. Ribonucleic Acid (RNA) <ul><li>Implementation of the genetic code: </li></ul><ul><ul><li>Many enzymes involved </li></ul></ul><ul><ul><li>Ribonucleic acid (RNA) crucial in protein synthesis </li></ul></ul><ul><li>RNA: </li></ul><ul><ul><li>Similar to one strand of DNA </li></ul></ul><ul><ul><li>Ribose replaces deoxyribose </li></ul></ul><ul><ul><li>Uracil replaces thymine </li></ul></ul><ul><li>Protein synthesis </li></ul><ul><ul><li>Transcription : RNA assembled along one strand of DNA </li></ul></ul><ul><ul><li>Go to assembly point of amino acids </li></ul></ul><ul><ul><li>Translation : RNA attaches amino acids into chains making proteins </li></ul></ul>
  12. 16. Mutations and Evolution <ul><li>DNA is the mechanism for Darwin’s theory of evolution </li></ul><ul><li>DNA replication is fast and accurate : </li></ul><ul><ul><li>Minutes for some bacteria </li></ul></ul><ul><ul><li>A few hours for the entire 3-billion human genome </li></ul></ul><ul><ul><li>Less than one mutation (error) per billion bases </li></ul></ul><ul><li>Causes of mutations: </li></ul><ul><ul><li>Ultraviolet (UV) light </li></ul></ul><ul><ul><li>Chemical agents (carcinogens) </li></ul></ul><ul><ul><li>Nuclear radiation (mostly natural cosmic rays) </li></ul></ul><ul><li>Effect of mutations: </li></ul><ul><ul><li>Harmless </li></ul></ul><ul><ul><li>Fatal </li></ul></ul><ul><ul><li>Evolution </li></ul></ul>
  13. 17. Will Life Elsewhere Use DNA? <ul><li>Heredity and evolution are essential </li></ul><ul><li>DNA does the job on Earth today </li></ul><ul><li>RNA may have been the first mechanism </li></ul><ul><li>Who’s to say that the same complex mechanism is universal? </li></ul><ul><li>Some type of molecule has to provide the mechanism for heredity and evolution </li></ul>
  14. 18. Extremophiles <ul><li>Volcanic vents : </li></ul><ul><ul><li>Water temperature reaches 400  C (750  F), possible because of the large pressure </li></ul></ul><ul><ul><li>Black smokers: mixed with nasty volcanic chemicals </li></ul></ul><ul><li>Antarctic dry valleys : </li></ul><ul><ul><li>Microbes in small pockets of water in rocks </li></ul></ul><ul><li>Lithophiles (rock lovers): </li></ul><ul><ul><li>Several kilometers below the surface </li></ul></ul><ul><ul><li>Chemical energy from rocks </li></ul></ul><ul><ul><li>Carbon from CO 2 filtering down </li></ul></ul><ul><li>Endospores (e.g., anthrax) </li></ul><ul><ul><li>Can lay dormant for long periods </li></ul></ul><ul><ul><li>Can survive lack of water, extreme heat and cold, and poisons </li></ul></ul><ul><ul><li>Some can survive in vacuum </li></ul></ul>
  15. 23. Implications for Extraterrestrial Life <ul><li>Oxygen for eukarya on Earth for only ~10% of its life </li></ul><ul><li>What is the probability that eukarya-like organisms would develop? </li></ul><ul><li>We are more likely to find extremophiles elsewhere </li></ul><ul><li>Extremophiles may be the norm, not the exception </li></ul>

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