Week 5 - Endosymbiosis

In this class I've learned what is endosymbiosis and what organelles had undergoes this endosymbiosis process. Endosymbiotic theory suggest that the large host cell and ingested bacteria become dependent on one another for survival, resulting in a permanent relationship. Besides, eukaryotes arose from a symbiotic relationship between various prokaryote, hetetrophic which is aerobic bacteria became mitochondria and cyanobacteria (photosynthetic) became chloroplast.

Next we are asked to determined whether mitochondria and chloroplast are originated from prokaryotes. Firstly, I really didn't expect that this organelles originally are from either prokaryote or eukaryote. I thought that the cell somehow already have those organelles, through evolution or they are born having those organelles. But after this class I realize that it is not. They undergo a process call endosymbiosis which they enter the cell through endocytosis and become a part of the cell. Mitochondria and chloroplast are originated from prokaryotes, due to some of the reasons.

1. The DNA of this organelles are circular which is the same as prokaryotes.

2. The size of the ribosomes is 70s, is the same as prokaryotes. While eukaryotes is 80s.

3. Mitochodria, chloroplast and prokaryotes replicated through binary fission. 

There is also other factors such as size. Hence all this characteristics show mitochondria and chloroplast are originated from prokaryotes. 

Next we learn about cell cycle. In form 5 and form 6 I learn about interphase, mitosis and meiosis. That's the only thing I've learned before. Last time we only cover a little about interphase, I actually dont really know what the cell do during that phase. In this class I just knew that there are a lot of stages before the cell are ready for mitosis. There are Gap 1, synthesis stage and Gap 2. Gap 1 and Gap 2 is basically the preparation for the cell before they enter the mitosis stage. While the synthesis stage are the stage where the DNA is replicated. Each stages needed a specific enzyme for them to work, the enzyme in Cyclin together with the Cyclin Dependent Kinase. 

The new next term that I learned is totipotency, the ability of any cells to form the organism back at favorable conditions. Scientist use this theory to make test tube plants, to replant a plant by just using the plant cell. For example, the leaf is dediferentiate into callus ( a group of undifferentiated cells), then it will re-differentiate into embryo, shoots and roots, forming a new plant. That's all for week 5.