EK 1001 Biology - Cell Bio Question

[sxld_cu]

This is #439 in the EK 1001 Biology book:

Peroxisomes and which other cellular organelle are self-replicating?
A. nucleus
B. mitochondria
C. ribosomes
D. DNA

The correct answer is B.

I am familiar with the endosymbiotic theory of mitochondria and eukaryotic cells. However, I thought that the mitochondria required enzymes and cellular machinery that was only present in the nucleus in order to replicate. I thought that the nucleus was self-replicating (via mitosis) so I picked A.

Can anyone help me solve this problem? Thank you in advance!

---

Members don't see this ad.

 

[Shinobiz11]

I believe this is alluding to specific mitochondrial DNA, giving it the ability to reproduce. The other the options require the cellular machinery and DNA of the cell.

 

[NextStepTutor_1]

@Shinobiz11 is right. This questions alludes to the fact that the mitochondria has all the required machinery to reproduce on it's own. A distinction EK is making in this question is between self-replicating and mitosis (not necessarily the same).
To look at the other answer choices, we see that D is incorrect because for DNA to replicate we need a large host of proteins. This is the same for the replication of the nucleus as well as other ribosomes. These 3 answers choices represent parts of the cell whose replication is not independent.

 

[sxld_cu]

Hi @Shinobiz11 and TJ Thanks so much for taking the time to answer my question!
After browsing online, I do agree that mitochondria are self-replicating (they can replicate their DNA but lack the mitotic apparatus to successfully undergo mitosis, as you said) but I am still confused about how proteins are involved.

Choice D is obviously wrong because DNA is not an organelle and ribosomes are just proteins so they cannot self-replicate. So, the answer is down to A or B, mitochondria or nucleus. Now, mtDNA still need a polymerase to replicate. Apparently it is DNA polymerase y, encoded by POLG (http://www.ncbi.nlm.nih.gov/pubmed/20927567) and I am guessing that this DNA polymerase is contained within the mitochondria. So mitochondria also require protein to replicate. How is this different from nucleus/DNA replication that also involves a host of DNA polymerases, etc. ?

 

[Shinobiz11]

Hi @Shinobiz11 and TJ Thanks so much for taking the time to answer my question!
After browsing online, I do agree that mitochondria are self-replicating (they can replicate their DNA but lack the mitotic apparatus to successfully undergo mitosis, as you said) but I am still confused about how proteins are involved.

Choice D is obviously wrong because DNA is not an organelle and ribosomes are just proteins so they cannot self-replicate. So, the answer is down to A or B, mitochondria or nucleus. Now, mtDNA still need a polymerase to replicate. Apparently it is DNA polymerase y, encoded by POLG (http://www.ncbi.nlm.nih.gov/pubmed/20927567) and I am guessing that this DNA polymerase is contained within the mitochondria. So mitochondria also require protein to replicate. How is this different from nucleus/DNA replication that also involves a host of DNA polymerases, etc. ?

You're thinking about this in too much detail.

From studying, it should be known that mitochondria have their own set of genetic machinery (endo-symbiont theory) and are able to replicate themselves. All of the other choices represent organelles or structures that don't have an independent source of reproduction and rely on the cell for their replication.

Choice D is the throwaway answer because it seems to obvious and the question asks about organelles, not cell contents.
Choice C is wrong because ribosomes are typically made of rRNA/proteins and it should be known how those structures come to be.

Now you're down at A and B as you said. Think about it carefully; the nucleus only replicates during mitosis and based on the previous known information about mitochondria, it should be evident that B is the answer.

 

[The Brown Knight]

mitochondria not only have their own genome but also their own replication enzymes; these enzymes and several of the mitochondrial membrane proteins are encoded by the mitochondrial genome and NOT necessarily the nuclear genome. Also, the mitochondria replicate by binary fission - for MCAT purposes treat it like an independent bacterium within the cell. If the economy crashes in the rest of the cell, the mitochondria won't be affected as much.
The nucleus doesn't exactly REPLICATE itself - does the nucleus itself split in two during any stage of the cell cycle? And of course, DNA requires outside machinery in the form of DNA polymerase and other proteins to replicate; some RNA on the other hand is self-replicating.