« An Illuminating Notion | Main | Gifts from Above »


Autumn Cochrane

In order to become an organelle, wouldn't the endosymbiont first have to "give up" most of its genome to the plant cell? Because, organelles might have one little plasmid of DNA, but they are not free-living inside their cells. Also, how would it be possible for the circular bacterial chromosome to be taken up into the linear chromosomes of a plant cell? I know that theoretically it can occur, especially in a lab. But in nature, after plants have been evolved to deal with linear chromosomes and have been doing so for ages, isn't it a little late? I mean, when mitochondria and chloroplasts became organelles, it was obviously very early in evolutionary history, possibly during a transition stage of cells when they actually could have had circular chromosomes. This would have made the process infinitely easier to occur naturally. I just can't see that happening in nature during this time period. May be, if the world exploded in nuclear war, the radiation would revert genomes back into circular DNA, and a whole slew of new organelles could arise...


Would that every student in their first microbiology class were as enthusiastic and questioning as you! Indeed, the endosymbiont has to give up much to become an organelle. Some of its genes are transferred to the nuclear chromosomes of the host, others are completely lost. Circular chromosomes insert into linear ones readily. Plasmids and phage, for example, do this all the time. You can see how by drawing this out on paper. With the circular chromosome next to the linear one, make a break in both chromosomes and rejoin each end of the circle to one of the ends of the linear chromosome. Voila! There are some other related posts on our blog that you might find interesting: Play It Again, Cyan, Some Like It Linear, and (for a mitochondrial digression), From Free-Living Bacterium to Cellular Citizen.


Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been saved. Comments are moderated and will not appear until approved by the author. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment

Comments are moderated, and will not appear until the author has approved them.

Your Information

(Name is required. Email address will not be displayed with the comment.)