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Midterm

BIOL 215 Notes for Midterm.doc


Department
Biology
Course Code
BIOL 215
Professor
Catherine Potvin
Study Guide
Midterm

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Sept 3 2009
Lecture 2: Origin of Earth and Life
Origins of Elements and Earth
A chronological history of Earth
4.6 bya origin of earth approximately
4.2-3.8 bya RNA world
3.8-3.75 bya Metabolism; DNA/Protein world
3.8-3.7 bya Origin of life
3.5-2.8 bya Origin of photosynthesis
2.5-2.0 bya Change from anoxygenic to oxygenic environment
1.7 bya oldest eukaryotes fossils
1.2 bya first multicellular organisms
250 mya Pangaea supercontinent forms
65 mya dinosaurs went extinct
6 mya earliest humans
Big Bang is dated 10-15 bya
quarks - hypothetical building blocks that fuse together to form
protons and neutrons which then go on to form hydrogen and helium
molecules
protostars are formed by nuclear fusion of hydrogen and helium
atoms. This reaction yielded lots of energy, which created a dense core
forming elements to iron while burning.
Once the core is composed largely of iron the protostars stop burning. It
had consumed most of the fuel (h and he) once fuel is exhausted the protostar
explodes to form a supernova releasing all of the elements into space as hot
gases
The sun is created
Planets around the sun form from gradual accumulation of solid matter
called ‘planetisismals’
Earth was initially molten and composed of largely Fe, Mg, Si and O
Earth formed 4.6 bya
Crust forms 4.2-4.1 bya as earth cools

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Meteors and comets bombard Earth 4.5-3.8 bya supplying lighter
elements and frozen gases)
4.6 bya 4.2-4.1 bya 4.0 bya 3.7 bya
Earth forms crust forms comets & meteors oldest
fossils
Primitive Earth’s atmosphere
Generated by volcanic out-gassing (80%) and impact bodies (20%)
CO2 (100-1000 x greater than present) N2, H20
Atmosphere reducing (reducing gases, electron taking)
NO FREE O2 in atmosphere initially – important since 02 would have
prevented the build-up of organic molecules
Very dense atmosphere (12 bar compared with 1 bar at present)
Primitive Earth’s Ocean
Volatile substances such as the oceans remained in the atmosphere
due to extreme heat
Once earth cooled to <100ºC water condensed and formed oceans
Large impact bodies would have vaporized the entire ocean, destroying
any life
Earth had liquid water on it’s surface by 3.8 bya (sedimentary rocks)
LIFE AT 3.7 BYA in the form of Stromatalytes (blue green algae
(cyanobacteria))
oAlso in form of organic matter found in rocks (C13-C12 ratio) indicates
that life had evolved by 3.7 bya
Once the oceans formed all atmospheric gases will dissolve in water
due to high solubility
These acids then dissolved rocks on land by the process of ‘chemical
weathering’ and rivers carried these salts to the ocean making it salty and
adding all elements that would be used by organisms
Characteristics of Life

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1. Organization
organs, tissues, organelles to carry out specific functions
2. Energy use and metabolism
To build new structures. Involves series of chemical reactions.
3. Homeostasis
Maintains consistency of internal composition in spite of external
environment
Ex. ionic composition of a cell – must maintain water levels and dispose
of waste
4. Replication/reproduction
Exact copy of genetic material is provided to offspring
5. Response to environmental stimulus
Ex. plants bending towards light
Origin of Building Blocks
Prebiotic chemistry Pre-RNA world RNA World DNA/Protein World Primordial
Cell
Origin of life is known through lab research on chemical reactions that may have
occurred 4.7 bya
Step 1 – Raw materials (simple organic matter such as amino acids, hydroxy
acids, sugars, purines, pyrimidines and fatty acids) Miller-Urey
Step 2 – Simple organic matter is linked together into polymers with properties
of replication
RNA
Step 3 – Reverse Transcriptase copies RNA into DNA which replicates
Step 4 – RNA from DNA builds Proteins and Lipids which form spheres
Step 5 – Compartmentalization – the formation of an outer membrane that
encased the nucleic acids and proteins. Likely started with Liposomes
(bubbles of lipid forming a sealed sphere)
Miller-Urey Experiment 1953
The experiment used water (H2O), methane (CH4), ammonia (NH3),
and hydrogen (H2). The chemicals were all sealed inside a sterile array of glass
tubes and flasks connected in a loop, with one flask half-full of liquid water and
another flask containing a pair of electrodes. The liquid water was heated to
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