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Chapter 2

BIOL 1000- ORIGINS OF LIFE (chap#2)

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York University
BIOL 1000
Julie Clark

Tanya Sivamanoharan Fri, Sept, 16/11 Biology- Chap# 2 Notes ORGINS OF LIFE 2.1- What is Life? - A frog moving and a rock sitting still shows a form of life in the frog and shows the trait of non-living objects such as the rock -this however does not create a big diff. at the molecular level -types of atoms and molecules found in living an non-living are not too diff. -the chem. and physics of biotic forms and abiotic things are similar 2.1a- Seven Characteristics that All Forms of Life Share -there are 7 char. to determine life that are common to all life forms 1. -DISPLAY ORDER arranged in highly ordered manner, with the cell being the fundamental unit of life 2. -HARNESS AND UTILITY ENERGY acquire energy from envir. and use it to maintain highly ordered state 3. -REPRODUCE have the ability to reproduce 4. -RESPOND TO STIMULI organism can make changes to structure, function, and behaviour by changes in environment 5. -EXHIBIT HOMEOSTASIS able to regulate their internal envir. so body conditions remain constant (Ex: sweating helps regulate body temp. despite external envir.) 6. -GROWTH AND DEVELOPMENT organisms increase in size by increasing # of cells 7. -EVOLVE organisms change over time in order to adapt to their changing envir. -some scientist consider a virus abiotic although it shows characteristics of life, b/c they use proteins and other cellular machinery of host cells in order to reproduce 2.1b- The Fundamental Unit of Life Is the Cell -there are 3 generalization to the cell theory 1. -all organism are composed of one or more cells. 2. –the cell is the smallest unit that has the properties of life 3. –cells arise only from the growth and division of preexisting cells 2.2- The Chemical Origins of Life -the third theory of cells suggest that cells can only be created from the growth and division of preexisting cells st -contradictory to the theory how was the 1 cell formed? -there must have been a time when no cells or life existed 2.2a- 4.6 Billion Years Compressed to1 -earth is app. 4.6 billion yrs. old -(figure 2.5 pg# 26) gives us an analogy of the 4.6 billion yrs, condensed into 1 yr. -on this 1 yr. calendar, 1 day= 12.6 million yrs. and 1 sec.= 143 yrs. -according to one yr., earth would have been formed on January 1 st 12:00am -earliest chemical evidence of life was not found until mid-march with a fossil evidence of prokaryotic life -eukaryotic cells were not discovered until early July -animals did not make an appearance until mid-October -land plants came along early November -dinosaur extinction happened in late-December and that’s when humans evolved -humans have only existed for a short period from Dec.31 11:42pm 2.2b- Conditions on Primordial Earth -dating methods show that the earth, sun and he other planets of the solar system all formed around the same time -solar system was formed by condensing gravity of matter within a molecular cloud -all the pressure and heat from the center of the cloud formed the sun -the remaining spiraling dust and gas in the cloud condensed into planets -originally earth was said to be a shell of a rock from the solar system with volcanic eruptions -earth eventually gave off heat radiation and cooled down and formed rocks, it took app. 500 million yrs. for earth to cool down to temp. for dev. of life -earth’s size gave it enough gravitational energy to hold an atmosphere around it -the atmosphere 4.6 billion yrs. ago was quite diff. from the one today -initially the atmos. contained water vapour, hydrogen sulfide, carbon dioxide, ammonia, and methane (it was said to be a reducing atmosphere) -today’s atmos. contains app. 21% oxygen (known to be an oxidizing atmosphere) 2.2c- The Miller-Urey Experiment -lack of oxygen in the early atmosphere meant that there was no ozone layer to protect earth from UV radiation -2 scientists, Oparin and Haldane concl. that UV light along with lightning combined with the reducing agents in the atmos. was essential for the simple building blocks for life -Stanley Miller, a student of Harold Urey and graduate of the University of Chicago tested the hypothesis of Oparin and Haldene in 1953 and found that it was true -Stanley Miller combined early atmospheric matter incl. hydrogen, methane, ammonia, and water vapour together in a closed setting and exposed it to energy -one week into the experiment, he saw many organic compounds in the water incl. urea, amino acids, and lactic, acidic, and acetic acids -the Miller-Urey study proved that molec. nec. for life can be formed abiotically very easily 2.2d- The Synthesis of Polymers from Monomers -key building blocks of life incl. nucleic acid and proteins are not individually synthesized molecules (monomers) -they are macromolecule with many subunit monomers creating a polymer chain (Ex: nucleic acids are polymers from nucleotides, proteins are polymers from amino acid monomers) -synthesis of proteins and nucleic acids require catalysts called enzymes to link 100s and 1000s of monomers together -it was believed that in the primitive times, a simple polymer with as many as 50 monomers was enough for activities like storing info. like nucleic acids -it was doubted that polymerization happened in water envir. b/c the polymers would have broken down or hydrolyzed -it was thought that solid and especially clay was a good surface for polymerization to occur on -clay in early earth absorbed ions, organic material, and energy that was used for polymerization and other reactions to take place 2.2e- Protobionts- The First Cells -protobiont group of abiotically produced organic molecules, surrounded by a membrane or a membrane-like structure -protobionts allow for an external and internal envir. 2.3- The Origins of Information and Metabolism -there are two critical processes nec. for the development of life 1. –dev. of a system for storage, replication, and translation of info. for protein synthesis 2. –dev. of metabolic pathways that would capture and harness energy for metabolism 2.3a- The Origin of the Information System -all organisms contain DNA -DNA a double-helix molecule with special alpha. sequences that carry info. needed for processes of the cell -DNA is similar in all organisms -info. in DNA is copied onto single stranded RNA -RNA directs production of protein molecules -there are thousands of proteins in cells that are each coded by unique DNA seq. -enzymes catalysts are req. to replicate DNA, transcript DNA into RNA, and to translate the RNA into proteins -the DNA replicates so that offspring have the same molecular instructions as the parent -changes in the DNA are how evolutionary change occurs over generations 2.3b- Ribozymes Are Biological Catalysts that Are Not Proteins -scientists wondered how DNA to RNA to proteins occurred while it required the product itself, proteins to catalyze the process -in 1979 an answer to this evolved where Thomas Czech found a group of RNA molecules called ribozymes that acted as catalysts -ribozymes can catalyze reactions on originating RNA molecules as well as other RNA molecules -a prediction was thereafter made that early life could have existed in RNA b/c of their ability to carry info. and act as a catalyst -before the discovery of ribozymes, proteins were known to be the only biological catalysts 2.3c- The Evolution of Proteins and DNA -the question is if RNA could carry info. and be a catalyst, why is life dominated by DNA and proteins? -this is b/c DNA does info. storage and proteins do catalysis far better than RNA on it’s own -therefore organisms with DNA and RNA have an adv. over organisms with RNA alone -the modern ribosomes are composed by two-thirds RNA and one-third protein -therefore ribosomes can be considered a type of ribozyme -RNA molecules that can synthesize even a little protein is positive b/c proteins are far more efficient than RNA molec. -the catalyzing power of any enzyme is higher than any ribozyme -proteins are also more diverse b/c they are composed of 25 diff. amino acids whereas RNA is only composed of 4 diff. nucleotides -amino acids can also bond with other amino acids but nucleotides cannot -proteins are dominant in cells b/c of its versitality -DNA would have developed after proteins, in an RNA world -DNA molecules are double-stranded and are far more complex than RNA molec. also containing the sugar deoxyribose sugar -DNA may have been favoured later in life b/c it is a better way to store info. than RNA for 3 reasons: 1. –each strand of DNA is more stable than strand of RNA b/c of the deoxyribose sugar 2. –the DNA uses thymine instead of uracil found in RNA b/c cytosine is usually mutated into uracil, so by using thymine we know that any uracil in a DNA is a damaged cytosine making it easier to repair 3. – DNA is double-stranded, so if a mutation occurs the complementary strand can be used to repair the damage -the stability of DNA makes it easier to store and preserve genetic info. 2.3d- The Development of Energy- Harnessing Reaction Pathways st -oxidation-reduction reactions were 1 energy releasing reactions of primitive cells -in human body, we oxidize food molec. (sugar) and use the nergy from that to reduce other molec. -in primitive cells the oxidized electrons would have been transferred to substance being reduced -this is not efficient and wastes energy and electron transport chains were nec.. -ATP evolved for linking energy-releasing reactions with reactions that req. energy -because of ATP’s efficiency of energy transfer it became a primary connector of reactions 2.4- Early Life 2.4a- Early Evidence of Life -earliest evidence of life was found in fossilized remains called stromatolites, about 3.5 billion yrs. ago -stromatolites type of layered rocks formed when microorganisms put sediment particles together -modern day stromatolites are formed by photosynethetic prokaryote called cyanobacteria 2.4b- Could Life Have Come to Earth From Space? -it is a hypothesis that life on earth could be from space -there are 2 points that support extraterrestrial origin of life on earth: 1. –earth was formed 4.6 billion yrs. ago and fossil evidence show life on earth 3.5 billion yrs. ago and chemical evid. shows that life on earth existed form 3.9 billion yrs. ago but scientists say that after the cooling time needed for earth to harden it was too short of a period for life to have formed on earth so fast after the cooling process 2. –research shows that life could survive in space for years, and there are organisms called extremophiles , usually prokaryotes that can live dormant in harsh conditions of space where the spores could have been restored on earth being the simplest form of l
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