NIS - BIOLOGY

1. NIS - BIOLOGY Lecture 61 – Lecture 62 The Origin of Life OzgurUnal

2. People have speculated about life’s origin for centuries. • However, it has been only for the past sixty years or so that scientists have experimented to understand how life might have begun. • What environmental conditions do you think scientists might stimulate to investigate the origins of life? Earth’s Early History

3. The oldest idea about the origin • of life: Spontaneous generation • Spontaneous generation is the idea that life arises from nonlife. • Example: Waste food and mud give rise to worms, insects etc. • Make sense? Think about it... Spontaneous Generation • Francesco Redi, in 1668, investigated spontaneous generation. • He hypothesized that flies produced other flies. • In his experiment, he observed maggots (larvae of flies) appeared only in flasks that were • open to flies. • Closed flasks had no flies and no • maggots  Figure 14.11!!

4. Spontaneous generation was replaced by the theory of biogenesis in the 19th century. • The theory of biogenesis states that only living organisms can produce other living organisms. • Check out Figure 14.12 for Pasteur’s experiment on the theory of biogenesis. • http://bcs.whfreeman.com/thelifewire/content/chp03/0302003.html Theory of Biogenesis

5. If life can arise only from pre-existing life, then how did the first life form appear? • We need to consider the first environmental conditions on Earth.. Origins: Modern Ideas • Most biologists agree that life originated through a series of chemical events early in Earth’s history. • During these events, complex organic molecules were generated from simpler ones. • Eventually simple metabolic pathways developed.

6. The primordial soup hypothesis was an early hypothesis about the origin of life. • In 1920, Alexander Oparin and John Haldane suggested that organic molecules could have been synthesized from simple reactions involving the gases in the early atmosphere of Earth. • UV radiation and lightning could have been the primary energy sources. Origin: Modern Ideas

7. In 1953, Stanley Miller and Harold Urey showed that simple organic molecules could be made • from inorganic compounds. • Check out Figure 14.13 for • Miller-Urey experiment!! • http://glencoe.mcgraw-hill.com/sites/9834092339/student_view0/chapter26/animation_-_miller-urey_experiment.html Miller and Urey Experiment

8. Later, other scientists found that HCN could be formed from even simpler molecules in early Earth atmosphere. • HCN can react with itself to • form adenine nucleotide base Origins: Modern Ideas • Making Proteins: • Once the amino acids were formed, how were proteins synthesized? • Check out Figure 14.14!!

9. How about the genetic code? How was it formed? • RNA as the first coding system?.. • And what processes made the transition from biological molecules to the cells? • Most of these details are still unknown.. Origins: Modern Ideas

10. Compare and contrast prokaryotic cells and eukaryotic cells. Cellular Evolution

11. There is chemical evidence of life from rocks that are 3.8 billion years old. • The earliest fossils are 3.5 billion years old (found in volcanic rocks)  life in volcanic environments • Scientists hypothesize that the first cells were prokaryotes. Cellular Evolution • Many scientists think that archaea are the closest relatives of Earth’s first cells. • Archaea are prokaryotic cells that often live in exteme environments, such as volcanic vents or hot springs.

12. Scientists think that oxygen was absent from Earth’s earliest atmosphere. • Oxygen was first produced by cyanobacteria about 3.5 billion years ago. • The first oxygen produced combined with iron to form iron oxide. This iron oxide is today found in layers of rocks. • After Earth’s free iron was saturated, oxygen started to accumulate in the atmosphere around • 1.8 billion years ago. • Why is free oxygen in the atmosphere • is so important? Cellular Evolution

13. Eukaryotic cells first appeared 1.8 billion years ago. • How? Endosymbiont Theory • Let’s have a closer look at the some of the organelles found in eukaryotes: mitochondria and chloroplast • Mitochondria and chloroplasts are about • the same size as the prokaryotes. • They contain their own DNA. • They have ribosomes similar to the ones • in prokaryotes. • They reproduce by binary fission (like • prokaryotes) independent of the cell.

14. In 1966, biologist Lynn Margulis proposed the • endosymbiont theory. • According to endosymbiont theory, the ancestors of eukaryotic cells lived in association with prokaryotic cells. • In some cases, prokaryotic cells might have lived inside eukaryotes and eventually become organelles inside eukaryotes. • http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter4/animation_-_endosymbiosis.html Endosymbiont Theory

15. In addition to the endosymbiont theory, Lynn Margulisand Dorian Sagan suggested that cells acquired other cells and genomes from other organismssymbiogenesis. • According to Margulis and Sagan, symbiogenesis is a major factor in the evolution of life on Earth. • They state that long term genomic mergers result in much greater evolutionary change than DNA mutations. • Do you agree with this hypothesis? Symbiogenesis