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Lecture 2

7 Pages

Biology (Sci)
Course Code
BIOL 111
Irene Gregory- Eaves

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Biology Lecture 2 9/6/2011 6:11:00 AM Pre-lecture Vocabulary - Prokaryote - Eukaryote - Unicellular - Multicellular - Metabolism - Photosynthesis - Aerobic - Anaerobic - Chemical Evolution - Spontaneous Generation - Monomer - Polymer - Condensation Reaction (Polymerization) - Amino Acid - Nucleotide - DNA, RNA (nucleic acid) - Catalyst Summary of lecture: origin and evolution of life, history of life and modern life. Life arose only once and from that point there is diversification and evolution of life. Evolution: genetic and resulting phenotypic change (observable property) in populations of organisms from one generation to the next  Evolution doesn’t occur within an individual or even in a generation, it occurs across generations  Working out evolutionary relationships is done by: fossil record (look at ways groups of animals changed over time), morphological (the body shape or plan of an organism) comparisons (extant vs. living vs. fossil), developmental records (it’s known the greatest similarities in body plan happens during early embryotic or larval stages) , molecular tools and analyses (ex: DNA, and entire genomes) and behavior of living organisms across different groups of taxa. Fossil Record: gives us information about when organisms first evolved (when they were first seen) and the environment in which they lived.  There are “living fossils”: the oldest species, representatives of these species were found in old fossils but still found today Morphological Comparisons: why evolution is important and in determining relationships between organisms  Examples: Acanthostega helps us understand why is choking so common in humans. They are a water and air breathing animal, in earlier ancestors there is a lung fish which have a lung sack which allowed it to breathe in low oxygen conditions. The ancestral bony fish evolved from the lung fish which had lung sacks that were cardio vascularized which lead to the tetrapod lung. Through this evolutionary sequence, the esophagus and the air pipe that we use to breathe and to eat are the same. It’s an evolutionary artifact. Evolutionary artifact: relationships between organisms and why things are how they are today Genetics analyses are revolutionizing our understanding: DNA analyses indicated that Neanderthals and humans interbred  Neanderthal: an organism that cohabitated with the homo sapiens in the past that are now extinct  Neanderthal DNA extracted from the leg bones (which were ~40000 yrs old)  60% of the Neanderthal genome has now been sequenced  Comparisons with human genome done this year, Neanderthal DNA fragments are scattered through genome of humans of non-African ancestry  Genetic analyses are greatly advancing our understanding of evolutionary relationships Hypotheses of origin of life on earth:  extraterrestrial source: the meteor from mars (we know this because the rock contained gasses that are only found on mars). They found building blocks for molecules that can build life  chemical evolution evidence: - The experiments of Miller and Urey (1950s): they used an apparatus and in the top chamber there was gasses known to mimic earth’s early atmosphere (CH4, N2, NH3, H2, H2O, CO2). They zapped it with electricity to mimic a lightning strike. They then condensed the compounds into the lower chamber and analyzed for simple organic compounds. They found the building blocks for molecules that build life: all 5 bases that are found in DNA and RNA, 17 of 20 amino acids used in protein synthesis and 3- and 6- carbon sugars. This experiment was replicated and it was found that Sulfide gas was in the mix of the gasses they used in experiment which were the recipe for life. A recipe for life:  Step 1: our building blocks which are monomers (amino acids, nucleotides and sugars).  Step 2: we need these to come together through condensation reactions where covalent bonds are forming excluding water. These reactions happen in clay shores, hydrothermal vents, under water and hot pools which are all used to catalyze reactions and speed up the process of the formation of polymers. Polymers that include proteins, carbohydrates, RNA/DNA and lipids which we need for life to form  Step 3: There is now evidence that RNA existed before DNA. They are simpler and act as a catalyst of these types of reactions. A folded piece of RNA is a ribosome. Shorter strands of DNA come on the ribosomes and form together and we get a single strand of RNA. So we have replication of genetic material through this catalyst action. We also need to create a separate environment from the external environment in order to maintain homeostasis (element for maintaining life). It’s been shown that we can make lipid bilayers  Step 4: Lipids naturally form bilayer spheres which encapsulate RNA providing a more stable environment. GET THE DIAGRAM OF IT. The lipid bilayer form a vesicle where a piece of RNA gets trapped inside and you get a protocell.  Step 5: Self replicating structure where there is an incorporation of nucleic acid from the external environment, nucleotides from the outside permeate the lipid bilayer and are incorporated in the nucleic acids (inside). Challenges of life: reproduce, transform energy and respond to environment The history of life calendar: On a 30 day calendar, life originated on day 4 and modern humans (Homo sapiens) arose the last 5 minutes of day 30, the last 5 seconds was the recorded date of Homo sapiens.  ~4.5 billion years ago- earth formed  ~3.8 billion years ago- origin of life (first evidence of life)  ~2.5 billion year ago- photosynthesis (prokaryotic unicellular life started to synthesize)  1.5 billion years ago- eukaryotes (have nucleus and membrane found organelles, more complex than the prokaryotes)  700 million years ago- multi cellular life  542 million year ago- “Cambrian explosion” (geological period which is very important because of the diversification and radiation of life)  420 million years ago- life on land (out of the oceans)  ~200 000 years ago- humans found on earth (first evidence of Homo sapiens) What’s happening with earth over time: physical changes  Con
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