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Chapter 22 Blog (Maria)

Page history last edited by Maria Chiaffarano 13 years, 1 month ago

In the first section of this page, you will write a daily summary of that day's class.  For example in  your chapter 2 blog, your first entry should be titled 9/3/10.  You should then write a one or two paragraph summary of that day's lecture, outlining the major points.  In the second section, you are required to add two items (link to a website, video, animation, student-created slide show, student-created PowerPoint presentation) and one journal article pertaining to a topic in this chapter.  A one-paragraph summary must accompany each item describing the main idea and how it applies to the lecture topic.  Please see the PBWorks help guide for assistance embedding video and other items directly in the page.  I will also produce a how-to video on using tables to wrap text around items and other useful tips.  Please see the syllabus for organization and grading details.


A.  Daily Blog


Blog for Chapter 22 Lecture (submitted 4/3/11):



     The Earth formed about 4.5 billion years ago, but life itself only began about a few hundred million years later.  The origin of life is significant because it helps scientists to have an understanding of what the world was like and how it evolved.  Evolution is studied on a large scale, but in this section, it is studied on a small scale.  Due to their simple structure, it was assumed that the earliest organisms were prokaryotes.  Fossils now support the presumption.  Stromatolites are banded domes of sedimentary rock.  They have assisted scientists in determining the age of different earthly materials.  About 2.5 billion years ago, the production of oxygen by early photosynthetic prokaryotes created an aerobic atmosphere.  This set the stage for the evolution of aerobic life. 

     The world is thought to have been dominated by RNA, or ribonucleic acid.  It was termed an “RNA world” because all living things had RNA as their genetic material.  RNA was used for information storage and catalytic functions.  Scientists tended to favor RNA as the first macromolecule that was found in protobionts, the first nonliving structures that evolved into living cells, because it has three key functions: RNA can store information in its nucleotide sequence, its nucleotide sequence can self-replicate, and RNA can perform a diversity of enzymatic functions.  DNA and proteins are not as versatile as RNA.  For example, DNA has limited catalytic activity and proteins cannot self-replicate.  However, RNA can perform functions that are characteristic of proteins while simultaneously serving as genetic material with its own replicative and informational functions. 

     Life cannot arise by spontaneous generation from inanimate material today, but conditions were very different when Earth was younger.  It was an anaerobic world where natural events such as lightning, volcanic activity, meteorite bombardment, and ultraviolet radiation were all more intense than we experience them today as well.  Therefore, over time, the world has evolved to use DNA, RNA, and proteins. 

     There are multiple stages of life and how it originated.  The first stage was the formation of life which involved the synthesis of organic molecules.  This formed a “prebiotic soup” which is the term for the medium formed by slow accumulation of organic molecules in the “early” oceans.  It formed over a long period of time prior to the existence of life.  Scientists have proposed many possible scenarios to explain the origin of life including the reducing atmosphere hypothesis, extraterrestrial hypothesis, and deep-sea vent hypothesis.  The second stage was the bonding of organic molecules to form polymers. The third stage is when the polymers became enclosed in protobionts (structures that separated them from the external environment).  The fourth stage was chemical selection, where molecules with functional properties increased in number.   



B.  Useful Materials




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