The endosymbiont theory

The endosymbiont theory

The link above shows an easy to understand animation on the endosymbiont theory.The endosymbiont theory suggests that mitochondria and chloroplasts were once prokaryotic cells that were taken inside or invaded by a eukaryotic cell and lived inside it. Both cells benefited from this as the eukaryotic cell was provided with energy. This was due to the prokaryotic cell being able to carry out metabolic reactions such as respiration and photosynthesis. In turn the prokaryotic cell was provided with nutrients.

Some evidence to support this theory is that both chloroplast and mitochondria have characteristics in common wit prokaryotes such as: double membranes, circular DNA that is circular and not enclosed in a nucleus, 70s ribosomes, reproduces by binary fission and is similar in size to them.

Note: 70s refers to the rate of sedimentation of the ribosome in a centrifuge. The “s” is a unit of measurement known as the Svedberg unit.


References :

Reece, J., Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson, 2010. Campbell Biology. 9th Edition Benjamin Cummings; 9th Ed.

Raven, P., George Johnson, Kenneth Mason, Jonathan Losos, Susan Singer, 2010.Biology. McGraw-Hill 9th Ed.

THE CELL (differences between prokaryotes and eukaryotes)

 Human Brain Cells

A cell is the smallest basic unit of structure and functions that is capable of performing the functions of life such as: growth, metabolism, stimulus response and replication. It was discovered by Robert Hooke.

All cellular organisms are categorized into two natural groups known as prokaryotes and eukaryotes. Prokaryotes do not contain a true nucleus as the name suggests (pro, before: karyon, nucleus). However eukaryotes do contain true nuclei (eu, true). Eukaryotes evolved from prokaryotes.

Bacteria are prokaryotes which have no true nucleus. That is the DNA is circular and lies free in the cytoplasm. They are small 0.5-10um, contain 70s ribosomes, belong to the kingdom Monera and have no membrane bound organelles. The cell walls are rigid and formed from glycoprotein mainly murein. In contrast, Protoctists, fungi, plants and animals are eukaryotes which have a true nucleus. That is the DNA is linear and enclosed in a nucleus. They are larger than prokaryotes 10-100um and contain 80s ribosomes. Also there are many organelles some which are double membrane such as mitochondria, chloroplast, nucleus and single membrane such as: Golgi apparatus, endoplasmic reticulum, lysosomes and vacuoles. The cell walls of fungi are rigid and consist mainly of chitin. Animal cells have no cell wall while the cell walls of plants are rigid and made up of cellulose.


N.P.O. Green, G.W. Stout, D.J Taylor, Biological Science 1&2. 3rd edition Cambridge.


For the rest of the semester it’s all things BIOCHEMISTRY!! It looks very interesting but challenging as well. Lets hope I can rise to the challenge and conquer this majestic beast :). My name is Danielle Ramsamooj and I am a first year student at the University of the West Indies St. Augustine. I am currently pursuing a degree in Biology and Chemistry. I aspire to one day have a career in the medical field…. not sure what as yet I’m still deciding. My hobbies are reading, swimming, football, cricket, dancing and last but not least sleeping. I have never done a blog before so lets hope I get it right. On this blog we would be journeying into the world of bio-chem and hopefully learn an experience new things along the way.