Question

1. The eukaryotic cell is thought to have arisen through an intimate association of an ancestral “pre-eukaryote”and a prokaryote. Briefly...

Name one energy yielding pathway the “pre-eukaryote” would have been using to generate ATP prior to its association with the prokaryote.

2. Describe the process of primary endosymbiosis.

3. With reference to your description in part 2 above,  name and describe two types of evidence that eukaryotic cells arose by endosymbiosis.

Answer 1

1. The pre- eukaryotes are the first formed cells, which in association (endosymbiosis) with prokaryotes make the eukaryotic cell today. During the course of evolution simple organic molecules were polymerized to produce macromolecules. RNA was the first formed genetic material.. So, the first cell formed was with RNA and some other molecules in a membrane, which is a phospholipid layer. Since RNA was the genetic material (with ribozyme activity), protein synthesis was resulted. The cell containing all these can be considered as the pro- eukaryotic cell. Since they lack mitochondrion for energy production, they met with some other mechanisms. In the first stages, energy was produced in the absence of oxygen, by the breakage of organic molecules. This is performed in the cytoplasm of the cell, and yielded ATP molecules. The method is like the 'glycolysis' in present day. Since aerobic respiration was absent, less number of ATP was produced.

2. Primary endosymbiosis is the process in which a living prokaryotic cell is engulfed by a eukaryotic cell. Later, the the engulfed organism is used for the purpose of host cell. For example, when the eukaryotic cell engulf a photosynthetic cyano bacteria, it is used by the host cell to being photosynthetic. This is the way how the chloroplast evolved inside the eukaryotic cell. Two features of chloroplast proves this idea.That is, the chloroplast has its own DNA. It has the power of self replication.

3. Evidence for eukaryotic endosymbiotic origin are mitochondrion endosymbiont and chloroplast endosymbiont..

mitochondrial endosymbiont was formed when the pro- eukaryotic cell has engulfed the bacterial cell with energy production. An example of such bacteria is 'purple non sulfur bacteria". During the course of evolution this bacterial cell was transformed to mitochondria. Presence of its own DNA in the mitochondria and its self self replicating capacity strengthens the theory.

Chloroplast endosymbiont is formed when a eukaryote with mitochondria has engulfed a cyanobacteria.Since the cyanobacteria has the capacity for photosynthesis, the eukaryotic cell also became photosynthetic during the time. Also, the chloroplast is self replicating with own DNA.