02.03A Early Cells (Honors)

They contain their own DNA, ribosomes, and are responsible for their own reproduction.

Describe the 3 main pieces of evidence supporting the Endosymbiotic Theory.

What is one more recent piece of evidence related to DNA that scientists have found?

Genomes

Describe Professor Kwang Jeon' experiment and what he observed.

In 1987, Professor Kwang Jeon of the University of Tennessee observed a number of amoebas (single-celled eukaryotes) that had ingested bacteria cells. The bacteria were killing off most of the amoebas, but a small number of the amoeba survived and returned to their normal modes. However, the invading bacteria were still present within surviving amoebas. Jeon continued to experiment with the amoebas and discovered that these surviving amoebas, and their offspring, could not survive without the bacteria. Jeon's discovery and experimentation proves it is possible for a cell to become dependent on an invading organism.

Describe how endosymbiosis worked.

Some of the oldest cells on Earth were single-cell organisms called bacteria, a type of prokaryotic cell. Fossil records show that prokaryotic bacteria cells covered the early Earth. Some of these bacteria adapted to make their own food using carbon dioxide from the atmosphere and energy from the sun. This process, called photosynthesis, produced oxygen that was released into the Earth's atmosphere. As the oxygen levels in the atmosphere increased, other organisms adapted and used that oxygen. Most of the membrane-bound organelles inside eukaryotic cells seem to have originated from deep folds in the cell membrane. However, the mitochondria and chloroplasts have distinct properties that make them different from the other organelles. These two organelles have characteristics similar to those of single-celled prokaryotic cells. According to the endosymbiotic theory, a large prokaryotic cell ingested another prokaryotic cell such as a bacterium. The bacterium was not digested by the cell but stayed intact inside its new host. The ingested prokaryotic bacterium cell performed aerobic respiration, a way to extract energy from organic molecules.The energy shared by the ingested bacterium gave the host cell an advantage over the other primitive cells. The ingested bacterium gained an advantage as well. It lives in a nutrient-rich environment inside its host cell. This bacterium is believed to be the ancestor of the mitochondria found in modern-day eukaryotic cells. The evidence supporting the endosymbiotic theory applies not just to mitochondria but also to the chloroplasts found in plant cells. Evidence suggests chloroplast organelles were once free-living bacteria that converted energy from sunlight in the process called photosynthesis. Over time, both the host cell and the bacteria cell it ingested developed a mutually satisfying or beneficial existence. Both entities lost their ability to function without the other. The endosymbiotic theory says that over time the internal cells evolved to become organelles, mitochondria, and chloroplasts within the eukaryotic cells.

Endosymbiotic Theory

The _____________ ______ hypothesizes that the ancestors of modern-day eukaryotic cells were actually two or more prokaryotic cells in a symbiotic relationship.

Endo

The prefix endo- indicates that one organism lives inside the other.

Symbiotic relationship

The relationship is symbiotic because the two organisms live together in a close relationship.

Two or more prokaryotic cells in a symbiotic relationship.

What did scientists believe was the early ancestors to our modern day eukaryotes?

The ancestors of modern-day eukaryotic cells were actually two or more prokaryotic cells in a symbiotic relationship.

What does the endosymbiotic theory hypothesize?

Human digestion

What is an example of an endosymbiotic relationship that is very important to us as humans?

Endosymbiosis

When one organism lives inside the other, it is called _____________.

Mitochondria & chloroplasts

Which two organelles found in eukaryotic cells have features in common with whole prokaryotic cells?