Question

Part B Directions Read Ch. 1 section 1.2 (pp. 4-10) and Ch. 19 1.Think about the origin of cellular life forms beginning from 4.5 billion years ago and continuing up to the point that eukaryotic cells appeared. Consider: Why is RNA thought to be the 1st self-replicating biomolecule? • Describe the endosymbiotic hypothesis and explain how it accounts for the origin of mitochondria, hydrogenosomes and chloroplasts. List at least 2 pieces of evidence that support this hypothesis. 2. Explain in your own words the differences between classical and molecular characteristics used in classifying organisms. Be sure you can provide several examples of both and describe the advantages, disadvantages/limitations associated with each type of characteristic. 3. Address the following information related to phylogenetic trees: a. Explain the purpose of phylogenetic trees and what information they convey. b. Outline the considerations used in building a phylogenetic tree and explain the significance of tree features such as nodes and branches and scale. c. Describe the challenges horizontal gene transfer introduces in the study of microbial evolution. Part Directions 1. Bergey's Manual of Systematics of Archaea and Bacteria (see Ch. 19, figure 19.9/19.13 - 10th ed) and a phylogenetic classification of Fungi (see Table 25.1/ 26.1 10th ed) both exist. What do we use for Protists? Does it have a formal hierarchical rank designation such as class and order? Why or why not?

Answer 1

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Answer 1:

RNA was the first genetic material. There is now enough evidence to suggest that essential life processes, such as metabolism, translation, splicing, etc., evolved around RNA. RNA used to act as a genetic material as well as a catalyst. In fact there are some important biochemical reactions in living systems that are catalyzed by RNA catalysts and not by protein enzymes. But, RNA being a catalyst was reactive and hence unstable. Therefore, DNA has evolved from RNA with chemical modifications that make it more stable. DNA being double stranded and having complementary strand further resists changes by evolving a process of repair.

The endosymbiotic theory explains that some cell organelles as we see today in eukaryotic cells were once prokaryotic cells. It explains that the first eukaryotic cell was more probably an amoeba like organism that managed to get its nutrients by the process of phagocytosis. It formed a nucleus when a piece of cytoplasmic membrane embraced around the chromosome. Some of these amoeba-like organisms ingested prokaryotic cells which had then survived inside the organism and developed a symbiotic relationship.

Mitochondrion was formed when a eukaryotic cell ingested a bacterium capable of aerobic respiration, chloroplasts were formed when a photosynthetic bacteria were ingested and hydrogenosomes were formed when organisms were exposed to aerobic conditions. They eventually lost their cell wall and part of their DNA because they were not beneficial to the host cell and could not survive outside the host cell.

There is much evidence to support this theory.

Mitochondria and chloroplasts have their own genetic material. They have circular DNA unlike eukaryotes that have linear DNA.

Mitochondria and chloroplasts have their own different ribosomal subunits which are 30S and 50S, unlike those in eukaryotes which have 40S and 60S subunits.