BISC120 Textbook Notes #2

BISC120 Textbook Notes #2 - Chapter 25 History of Life on...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Chapter 25 History of Life on Earth- Overview o Past organisms much different from those right now o Early Earth also different o Fossil records show evolutionary changes over large time scales Emergence of terrestrial beings Origin of photosynthesis Long-term impacts of mass extinctions Conditions on early Earth made the origin of life possible- Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages o Abiotic synthesis of small organic molecules o Joining of these small molecules into macromolecules o Packaging of molecules into protocells o Origin of self-replicating molecules- Synthesis of organic compounds on early Earth o Earth formed 4.6 billion years ago, bombardment ended 3.9 billion years ago o Early atmosphere contains water vapor and chemicals released by volcanic eruptions (N2, NO2, CO2, CH4, NH3, H2, H2S) o 1920s: A.I. Oparin + J.B.S. Haldane independently theorize that Earths atmosphere added electrons to the environment, thus permitting formation of simple organic molecules Energy for this couldve come from lightning and intense UV radiation o 1953: Miller + Urey test the hypothesis creating conditions Resulted in formation of amino acids found in organisms today, along with others; confirms how organic compounds have been key to origin of life and can be generated from abiotic synthesis However, still uncertain whether enough methane/ammonia was present to permit reduction; Early atmosphere made of mainly N 2 , CO 2 ; was neither reducing or oxidizing May have been synthesized near submerged volcanoes and deep-sea vents 1969: amino acids in meteorites confirm amino acid presents; we use L isomer o Abiotic synthesis of Polymers, Protobionts Amino acid polymers formed by dripping on hot hard surface; polymers formed spontaneously without help of enzymes/ribosomes But ofc, more complex mix of linked/cross-linked amino acids; probably acted as weak catalysts Protobionists: aggregates of abiotically produced molecules surrounded by a membrane(-like) structure Key properties of life: replication and metabolism Exhibit simple reproduction/metabolism and maintain internal chemical environment; from spontaneous abiotically produced org cmpds i.e.: liposomes (membrane-bound) form when lipids added to H 2 O o RNA World + Dawn of Natl Selection First genetic material: RNA; Cech finds that RNA can do lots of enzyme- like catalytic functions (ribozymes) Can make complementary copies of short pieces of RNA, self- splicing introns, act on different molecules (tRNA) Usually slow, but protein speeds up reaction rates RNA (SS) takes on various 3D shapes, has phenotype/genotype early protocells with self-replicating, catalytic RNA would be more effective using resources and would increase in numbers thru natl selection, surviving in diff environments Forms the RNA world - Fossil record documents history of life...
View Full Document

Page1 / 17

BISC120 Textbook Notes #2 - Chapter 25 History of Life on...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online