"What is the secret of life"
What is the secret of life? DNA: Structure & Function Lecture 4 Genetics & Society Honor 3215, Fall 2008 Bryan Benham 2 Feb. 28, 1953: Two guys walk into a pub and declare they have the answer. But let’s start at the beginning 3 4 One Answer: Vitalism Vitalism is the idea that living organisms possess an inner force or energy that gives them the property of Question- life. It is the idea that there is a property that distinguishes life from non-life What is Life? Variously developed in China as ‘chi’ In India as ‘prana’ Or simply as one’s life force or ‘soul’ 5 6 Early attacks on Vitalism OK, some biological reactions 1828 Friedrich Wohler synthesizes urea from inorganic are just chemistry, but how materials Substances normally produced by living organisms does a cell know how to be a are chemical compounds that can be made by non cell? -living sources 1897 Hans and Eduard Buchner show that fermentation Surely there is something can be accomplished in a cell free system. Fermentation, a reaction carried out by living different about life. organisms, is a chemical, not a vital process 7 8 20th Century Challenges to Mendel’s Laws Vitalism •! Mendel’s laws •! Show the rules of heredity are •! Morgan’s flies mathematically predictable (1866; rediscovered in 1900) •! Pneumonia S and R •! Müller’s radiation •! Also, that inheritance occurs in packets of information physically encoded (“factors”) 9 10 Morgan’s Flies The experiment 1933: Thomas Hunt Morgan wins the Nobel prize for demonstrating that chromosomes are the fundamental unit of inheritance. X Breed mutant flies Look at their chromosomes http://www.biol.unlp.edu.ar/historianobel-genetica.htm http://www.cofc.edu/~bernardoj/Genetics%20Lab/212Lhome.html 11 12 Observed Pneumonia S and R Traits can often be inherited together (linkage). 1944: Avery, McCarty and McLeod published a There are the same number of trait groups as paper that stated "Deoxyribonucleic acid there are chromosomes. (DNA) plays a central role in determining specific characteristics in the course of In rare cases when chromosomes are not reproduction. " inherited normally, the traits are also not inherited normally. Conclusion: Inheritance is on chromosomes, that is, things you can see in a microscope. Demonstrated that there is an observable, physical nature to cellular information 13 http://genetics.gsk.com/history.htm 14 The experiment The experiment + + Pneumonia Pneumonia Bacteria (S) Bacteria (R) 15 16 The experiment Müller’s Radiation 1946: Hermann Müller wins a Nobel Prize for his work on the genetic effects of radiation. + Pneumonia DNA alone is enough to Bacteria (R) make R into S Plus DNA from Conclusion: There is a Pneumonia chemical substance, DNA, Bacteria (S) that holds genetic information 17 18 http://nobelprize.org/nobel_prizes/medicine/laureates/1946/muller-bio.html The experiment X-rays Broken Question- chromosomes What do we know? Conclusion: The information can be changed through physical Mutant processes chromosomes Mutant offspring 19 20 Life has a physical basis But the question remained: Inheritance is on chromosomes. How does DNA make an organism? You can see them. DNA can carry new traits into an organism. Objection: Surely DNA is too simple to account You can hold it in your hand. for the complexity of life and its processes. Traits can be changed by physical processes. There must be something more to DNA than You can change it by hitting it with a hammer. chemistry. Is vitalism a serious option? 21 22 Enter two guys (another guy, a gal, her x-ray What did we know about picture and another guy’s findings about DNA? proportions of the four bases in DNA): •! It contains sugar, phosphate and nitrogen-containing bases: •! There are 4 bases- Adenine (A) Cytosine (C) Guanine (G) Thymine (T) 23 24 Watson-Crick DNA Model (1953) •!(Antiparallel) double helix The answer to the secret of life •!DNA bases in the published in the middle journal Nature April 25, 1953 •!Sugar Phosphate backbone running Only two months along the outside after walking into a pub… 25 26 Watson-Crick DNA Model (1953) •!(Antiparallel) double helix •!DNA bases in the middle •!Sugar Phosphate backbone running What was the secret of life? along the outside •!Bases are paired with each other: A-T C-G 27 28 DNA bases can only pair one way Why Complementarity? Everything in genetics relies on replication: A T reproduction (cell division, mitosis, meiosis) development (cell differentiation, growth… ) maintaining life (replacing skin, blood, muscle, bone…) Complementarity allows the hereditary G C information to be copied digitally; accurately, quickly, and efficiently. This is called complementarity 29 30 DNA can be very accurately DNA can be very accurately copied copied Even across species, through evolutionary history, accurate replication is important. This DNA sequence is still recognizable There have been hundreds of billions of cell divisions since the last common ancestor of these animals. in you since you were a single fertilized egg. And those copies have been very accurate, quick and efficient. If they weren’t, you (and me, everyone in this room, on campus, across the planet) would likely not be alive. 31 32 DNA Replication •! DNA splits/opens •! New bases added (via complimentarity) •! From one double stranded DNA, two identical daughter strands are reproduced "It has not escaped our notice that the specific pairing that we have postulated •! Repeated as necessary immediately suggests a possible copying mechanism for the genetic material" 33 34 Cool animation of DNA replication process at http://www.johnkyrk.com/DNAreplication.html DNA Replication DNA Replication Produces exact copies for many •! Precedes mitosis (cell division) and generations… meiosis (sperm and egg cells). •! Same basic process of replication, with a few differences, used in other DNA functions: transcription and translation. and so on… 35 36 How does the DNA information DNA is the blueprint result in an living organism? •! Blueprints are good for many things, but merely copying doesn’t provide all the answers… •! How does the DNA blueprint result in ? physical characteristics? http://giant-panda.com/ 37 38 How does the DNA information What is a gene? result in an living organism? A gene is a specific section of Genes DNA within a chromosome (usually several 10,000’s of base pairs long) http://giant-panda.com/ 39 40 http://cmgm.stanford.edu/biochem201/Slides/Chromatin%20Structure/01%20Human%20Chromosome.JPG What is a gene? A gene Proteins do things makes a protein. …such as make and maintain organisms and all their characteristics A gene is a section of DNA (usually several 10,000’s of base pairs long) 41 42 http://cmgm.stanford.edu/biochem201/Slides/Chromatin%20Structure/01%20Human%20Chromosome.JPG The discovery of the molecular structure Next Time: of DNA is yet another blow to vitalism, The Central Dogma & Gene Expression providing a physical/chemical explanation for life… DNA But more importantly for us now, knowing where genetic information is stored and how it functions RNA allows us to read and manipulate it… … welcome to the genetic revolution! Protein 43 44 Summary •! Watson and Crick •! Structure of DNA discover DNA –! Double helix •! Vitalism and life •! Challenges to –! Backbone Postscript –! Four bases: ATCG vitalism •! Complementarity –! Mendel’s laws –! Morgan’s flies •! DNA replication –! Pneumonia S and R •! Genes –! Müller’s radiation 45 46 Watson and Crick Nobel Prize 1962 47 48 a feminist icon a flawed perfectionist Video: Video: Secret of Photo 51 DNA: The Secret of Life http://www.pbs.org/wgbh/nova/photo51/ http://www.pbs.org/wnet/dna/index.html Call number: QP-624-D12-2004 Call number: QH506.F72 S43 2003 49 50 Websites of Interest •! Genetic Science Learning Center (U of U) –! http://learn.genetics.utah.edu/ •! Dolan DNA Learning Center’s Gene Almanac (Cold Springs Harbor) –! http://www.dnalc.org/home.html •! Human Genome Project Website –! http://genomics.energy.gov/ 51