A1) - The ancestor eukoryotic cells engulfed bacteria by phagocytosis/endocytosis, and the bacteria eventually became the mitochondria or chloroplast.
- Hence, the outer membrane is derived from the eukaryotic cell and the inner membrane is derived from the bacteria.
FYI only: This theory is actually named the "endosymbiotic theory", but you are not required to know it. You can watch an animation of the theory here: http://www.youtube.com/watch?v=EgaGh9-mFnQ
Note: Please do not be confused, prokaryotes (i.e. bacteria) have only one cell membrane. You will learn more about its structure in the later topics.
Q2) How does linear DNA (in eukaryotes) and circular DNA (in prokaryotes, mitochondria, and chloroplasts) look like under the electron microscope (EM)?
A2) Linear DNA (above) and circular DNA (below), in a relaxed state.
Miss Teong, in today's biology lecture, Miss Foo talked about how the white blood cells are able to locate and trace where the foreign particles are... I couldn't really catch it. Was it because there are complementary binding sites on the cell membrane of the white blood cell and the foreign particle :O?
ReplyDeleteHi Celestine,
ReplyDeleteInvading microorganisms such as bacteria release chemicals that binds to the receptors on the cell surface membranes of white blood cells. These chemicals are called "chemoattractants" because they attract cells to come nearer to themselves. And the process of cells moving according to chemical cues in the environment is called "chemotaxis".
You can take a look at the following video on chemotaxis:
http://www.youtube.com/watch?v=ZUUfdP87Ssg
For your reference, here's the URL of the video shown during lecture:
http://www.youtube.com/watch?v=EpC6G_DGqkI&feature=related
Hope that this is clear!
Ok(: thank you!
DeleteFor Qn 2 right, when we use the presence of double membrane to prove that it is of prokaryotic origin, the theory behind it is because of the phagocytosis of the bacteria by the ancestor eukayotic cells. My question is that since it is a theory only, why can we use it to prove since there is no evidence to support the theory?
ReplyDeleteHi Boon Xuan,
DeleteActually they have also found that there are proteins present in the inner membrane of mitochondria and chloroplasts that are similar to the proteins that are present on the membrane of bacteria. That is why they proposed the endosymbiotic theory. Hope that this is clearer? Let me know if you have further queries! :)
Oh, and you asked yesterday whether one evidence can be that the mitochondria and chloroplasts are autonomous/self-sustaining systems in the eukaryotic cells, thus they may have orginated as bacteria.
DeleteThis is a good observation, but actually mitochondria and chloroplasts are not entirely self-sustaining. That is why these two organelles are in a so-called "symbiotic relationship" with the eukaryotic cell, where the organelles depend on the eukaryotic cell and vice versa.
Some proteins in the mitochondria (mitochondrial proteins, for example, enzymes that carry out respiration), are actually transcribed/translated from the DNA in the nucleus of the eukaryotic cell (instead of the mitochondria's own DNA). Hence they are not entirely self-sustaining.
Hope that this is clear!
Thank you
ReplyDelete