Discussion of all aspects of cellular structure, physiology and communication.
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Hello, I have been a question like this. Autoradiography was used to study the production of proteins in liver cells by using a radioactive tracer over a time period of 20 minutes. The results are then given from which i have plotted a graph that shows the
Nucleus: very low amount of radioactive proteins after 5 minutes, which barely increase over the whole 20 minutes
R ER: After 5 minutes is high and then decreases over 20 minutes with the rate of decrease slowing down
Golgi Body: starts low then gets high, and continues to climb up to the 20 minutes
Mitochondria: after 5 minutes very low and barely increases, very similar to the nucleus.
I have to explain these problems and i have done a lot of research into them however i didn't get the explanations i wanted. For the nucleus, although there is no protein synthesis going on in the nucleus, lots of proteins have to enter it so it can function, production of ribosomes is just 1 example. Why don't the results increase more?
The R ER makes sense to me
The Golgi only modifies and packages the proteins, they are then released into three different types of vesicles. Why doesn't the data rise and then fall over the 20 minutes? or is it that the time frame for proteins to pass through the golgi is longer than 20 minutes (i would expect it too rise then level off, equilibrium, and then decline)
The mitochondria, although synthesizes some proteins, it imports far more, so why does it also stay low like the nucleus? is it that it's rate of protein uptake is very slow?
Just to let you know i don't have a lot of biology experience but i've been searching for the explanations to these questions and i've only found data which agrees with this data
Sorry about the long post, hope it makes sense. Any help would be really appreciated
I think, that in the case of nucleus and mitochondria is not the question about how fast, but how much I don't think, that nucleus and mitochondria use so much proteins from cytosol (BTW what has ribosomes to do with nucleus?). In nucleus, you basically need only chromatin, which synthesis depends on cell cycle phase, and some regulatory proteins (and stuff for replication, transcription, blabla), but that's not much of them. The same in mitochondria. Maybe if you searched for the mitochondrial genome of organism, whose cell have you used, you will see, how many proteins it actually needs from cytosol.
Cis or trans? That's what matters.
Thanks for the reply. I see that the protein intake of the nucleus and mitochondria are probably pretty small and so their results reflect this. (BTW aren't small and large sub units of ribosomes manufactured in the nucleolus? and doesn't this require ribosomal proteins to be imported into the nucleus?) Can you offer any advice about the Golgi body. Is it just that proteins take a long time to travel from the cis face to the trans face?
Thanks again for your help
Both the nucleus and the mitochondrion have double membranes. Takes longer for the tracer to enter a double membrane? as oppose to the golgi and RER? Or any other reason that the tracer would be slower to enter and be retained in these organelles?
Yes the tracer is a radioactive amino acid. It doesn't go into specifics, i think it's an A-level standard question. The time frame is 20 minutes so i'm not sure about the low rate for the nucleus and mitochondria being down to their double membrane. Thanks for the replys, i'm out of ideas
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