What is Endosymbiotic Theory?


10:49 AM

1 min read
What is Endosymbiotic Theory? Blog Image


Two papers published recently have generated new interest in the endosymbiotic theory.

About Endosymbiotic Theory

  • The endosymbiotic theory states that some of the organelles in today's eukaryotic cells were once prokaryotic microbes.
  • In this theory, the first eukaryotic cell was probably an amoeba-like cell that got nutrients by phagocytosis and contained a nucleus that formed when a piece of the cytoplasmic membrane pinched off around the chromosomes.
  • Some of these amoeba-like organisms ingested prokaryotic cells that then survived within the organism and developed a symbiotic relationship.
  • Mitochondria formed when bacteria capable of aerobic respiration were ingested; chloroplasts formed when photosynthetic bacteria were ingested. They eventually lost their cell wall and much of their DNA because they were not of benefit within the host cell.
  • The endosymbiotic theory describes how a large host cell and ingested bacteria could easily become dependent on one another for survival, resulting in a permanent relationship.
  • Over millions of years of evolution, mitochondria and chloroplasts have become more specialized, and today they cannot live outside the cell.

Prokaryotes vs. Eukaryotes

  • All living things can be divided into three basic domains: Bacteria, Archaea, and Eukarya.
  • The primarily single-celled organisms found in the Bacteria and Archaea domains are known as prokaryotes. These organisms are made of prokaryotic cells—the smallest, simplest, and most ancient cells.
  • Organisms in the Eukarya domain is made of more complex eukaryotic cells. These organisms, called eukaryotes, can be unicellular or multicellular and include animals, plants, fungi, and protists. 
  • The biggest distinction between them is that eukaryotic cells have a distinct nucleus containing the cell's genetic material, while prokaryotic cells don't have a nucleus and have free-floating genetic material instead. 
  • Eukaryotes developed at least 2.7 billion years ago, following 1 to 1.5 billion years of prokaryotic evolution.
  • Eukaryotic cells have several other membrane-bound organelles not found in prokaryotic cells. These include the mitochondria, rough and smooth endoplasmic reticulum, golgi complex, and in the case of plant cells, chloroplasts (conduct photosynthesis).
  • Although prokaryotic and eukaryotic cells have many differences, they share some common features, including the following:
    • DNA.
    • Cell (or plasma) membrane
    • Cytoplasm: Jelly-like fluid within a cell that is composed primarily of water, salts, and proteins.
    • Ribosomes: Organelles that make proteins.

Q1: What is Phagocytosis?

Phagocytosis, or “cell eating”, is the process by which a cell engulfs a particle and digests it. The word phagocytosis comes from the Greek phago-, meaning “devouring”, and -cyte, meaning “cell”. Cells in the immune systems of organisms use phagocytosis to devour bodily intruders such as bacteria, and they also engulf and get rid of cell debris. Some single-celled organisms like amoebas use phagocytosis in order to eat and acquire nutrients.

Source: Can the newly discovered organelle help engineer plants to fix nitrogen?