Ribosome Classification

[computerdorkdan]

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A ribosome isn't an organelle. It's not an inclusion either. Is it classified as anything?

 

[capn jazz]

A ribosome is just protein and rRNA... I don't think there's a classification.

 

[capn jazz]

unless you're talking about the ribozyme 😀 (one of my favorite words)

 

[computerdorkdan]

unless you're talking about the ribozyme 😀 (one of my favorite words)

Hmm, an enzyme made out of RNA. That's a pretty neat trick. I didn't know that one.

 

[capn jazz]

The ribozyme is named that due to the fact that it appears that the rRNA has the catalytic activity in the ribosome when it was previously unknown that RNA could catalyze rxns.

 

[engineeredout]

The ribosome is definitely an organelle. It just isn't a complex membrane-enclosed organelle.

 

[Bernoull]

I see no reason why ribosome isn't an organelle, so I second engineeredout.

 

[matth87]

isn't the definition of an organelle a membrane bound compartment?

Ribosomes are just rRNA and proteins. I see no membrane bound compartment.

Please let me know if I am mistaken. Thanks.

 

[capn jazz]

I'm going to change sides and go with wikipedia:
http://en.wikipedia.org/wiki/Organelle

An organelle is usually defined as being membrane-bound, but not always.

 

[computerdorkdan]

I'm going to change sides and go with wikipedia:
http://en.wikipedia.org/wiki/Organelle

An organelle is usually defined as being membrane-bound, but not always.

Hrm.

Well, prokaryotes have ribosomes. Does that muddle it up at all?

 

[capn jazz]

Yea, isn't the traditional wisdom that prokaryotes lack organelles? If so, then ribosomes aren't organelles.

This is really all semantics, but I can see a question like "Which of the following organelles..." and one of the choices is the ribosome but it's wrong because it's not an organelle to begin with.

 

[computerdorkdan]

Yea, isn't the traditional wisdom that prokaryotes lack organelles? If so, then ribosomes aren't organelles.

This is really all semantics, but I can see a question like "Which of the following organelles..." and one of the choices is the ribosome but it's wrong because it's not an organelle to begin with.

The wikipedia article has this in it: "Prokaryotes were once thought not to have organelles, but some examples have now been identified."

Here's the abstract from the article it cites:

http://www.ncbi.nlm.nih.gov/pubmed/16081736

Bacterial microcompartments are primitive organelles composed entirely of protein subunits. Genomic sequence databases reveal the widespread occurrence of microcompartments across diverse microbes. The prototypical bacterial microcompartment is the carboxysome, a protein shell for sequestering carbon fixation reactions. We report three-dimensional crystal structures of multiple carboxysome shell proteins, revealing a hexameric unit as the basic microcompartment building block and showing how these hexamers assemble to form flat facets of the polyhedral shell. The structures suggest how molecular transport across the shell may be controlled and how structural variations might govern the assembly and architecture of these subcellular compartments.

So, this sounds not like the "membrane-bound" organelles we're used to thinking of.

 

[engineeredout]

Its all semantics that are pretty irrevelant.

I found a question on an exam posted online:

3) Which of the following organelles is enclosed by an envelope of two membranes?

A) Golgi apparatus
B) lysosome
* C) chloroplast
D) central vacuole
E) ribosome


Now the answer is chloroplast, but it insinuates that all of the choices, including E) Ribosome, are organelles.


Point: If this is the only thing you have to worry about, you're in good shape for the MCAT. If not, go study something else.

 

[matth87]

Its all semantics that are pretty irrevelant.

I found a question on an exam posted online:

3) Which of the following organelles is enclosed by an envelope of two membranes?

A) Golgi apparatus
B) lysosome
* C) chloroplast
D) central vacuole
E) ribosome


Now the answer is chloroplast, but it insinuates that all of the choices, including E) Ribosome, are organelles.


Point: If this is the only thing you have to worry about, you're in good shape for the MCAT. If not, go study something else.

lol, the things that drive people like us insane.

 

[matth87]

Found this article from Google

Are ribosomes organelles?

It seems that there is a some debate on this topic and I would like to
put my two cents in.

It depends on your definition of an organelle. If you define an
organelle as any membrane-enclosed compartment in a cell, you would have
to conclude that ribosomes are not organelles. However, if you use a much
broader definition such as any structure within the cell which plays an
important role, you would call ribosomes orgnanelles. I tend to favor the
former definition because I believe that the term organelle implies a
membrane-enclosed compartment.

I do not agree with those who say that procaryotes don't have
membrane-enclosed compartments. Some do although the membrane is not a
phospholipid bilayer. This comment may initiate another debate!


Cheers.

Leo G. Leduc

 

[Red Leader]

Its all semantics that are pretty irrevelant.

I found a question on an exam posted online:

3) Which of the following organelles is enclosed by an envelope of two membranes?

A) Golgi apparatus
B) lysosome
* C) chloroplast
D) central vacuole
E) ribosome


Now the answer is chloroplast, but it insinuates that all of the choices, including E) Ribosome, are organelles.


Point: If this is the only thing you have to worry about, you're in good shape for the MCAT. If not, go study something else.

Actually since ribosomes is a wrong answer it could be there to trick people who don't know that ribosomes are not organelles.

Additionally, since ribosome = proteine + nucleic acid and you want to count it as an organelle, you have to say chromosomes are organelles too because that is just DNA + histones (proteins).

Therefore, I do not think ribosomes are organelles.

 

[computerdorkdan]

Point: If this is the only thing you have to worry about, you're in good shape for the MCAT. If not, go study something else.

You know, I think this discussion is pretty interesting. It's way better than the "OMG I VOIDED" conversations or the constant "which VR study is best for someone who got a 1 on VR" questions that show up on the MCAT forms. IMHO this is what the forums are for. That and I'm totally anal-retentive.

My vote is with ribosomes not being organelles. I'm gonna go look through some bio books in the lab and see what I dig up. Maybe I'll learn something else useful along the way.

 

[computerdorkdan]

Ok, so I was wrong...as far as I can tell.

There's 4 non-membrane bound organelles in a cell:

- microtubules
- ribosomes
- intermediate filaments
- microfilaments

See, I learned something. 👍

 

[capn jazz]

Did you get that from examkrackers? I was doing bio 1001 and noticed that exact statement in one of the solutions.

 

[computerdorkdan]

Did you get that from examkrackers? I was doing bio 1001 and noticed that exact statement in one of the solutions.

Yeup.