0
$\begingroup$

It is my current understanding that free ribosomes synthesise proteins to be used inside the cell, and the rough endoplasmic reticulum is necessary to make proteins that are to be secreted by the cell. Is this correct - and more importantly, if so, why?

$\endgroup$

closed as off-topic by David, kmm, AliceD Nov 16 '17 at 8:18

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework questions are off-topic on Biology unless you have shown your attempt at an answer. For more information see our homework policy." – David, kmm, AliceD
If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Please do some research before posting questions and demonstrate that you have done so in your question. This is basic material that can be found online and in standard biochemistry textbooks. $\endgroup$ – David Nov 5 '17 at 20:23
  • $\begingroup$ While the default textbook will likely cover co-translational transfer of nascent proteins into the ER (which topologically corresponds to the outside of cells), there are also other mechanisms that apply to some proteins and don't necessitate rough ER ( en.wikipedia.org/wiki/Exosome_(vesicle) ) $\endgroup$ – tsttst Nov 6 '17 at 0:24
  • $\begingroup$ Ahhh I did search for a while and found nothing (in terminology could comprehend anyway) and don't own a biochemistry textbook as I am not doing a biochemistry course $\endgroup$ – Elizabeth T Nov 6 '17 at 10:44
  • $\begingroup$ Cell Biology books also cover this. You need to buy books if you are studying. Sacrifice other things, but buy books. However you could have answered this question on the web using NCBI Bookshelf, which has older editions of some excellent texts, including Berg et al. Biochemistry, Alberts et al. Molecular Biology of the Cell, and Lodish et al. Molecular Cell Biology. Searching for Endoplasmic Reticulum brings up a list, which includes these three books, which you can then consult. Learn to save your own life. $\endgroup$ – David Nov 6 '17 at 17:27
  • $\begingroup$ I did research the question online beforehand - however perhaps the wording of my question brought up other results? I could find nothing that would help me when I searched. In the future, I will use that website as I've used it a couple of times (when it came up after a search) and it was very helpful $\endgroup$ – Elizabeth T Nov 15 '17 at 15:28
0
$\begingroup$

Extracellular proteins are proteins that function outside the cell, meaning they are made in cells (transcribed from ribosomes) and then are transported to the plasma membrane to be delivered to the extracellular space. The proteins that need to be secreted aren't secreted as free proteins, rather they are packaged into vesicles. Vesicles are membrane-enclosed structures. When ribosomes are translating mRNA and come across a specific sequence called a signal peptide (wiki), the ribosome goes to the ER and delivers the peptide into the ER. From here, the peptide gets packaged into a vesicle-- first a membrane budding off from the ER. enter image description here source(NCBI)

This is also how secretory proteins get into the Golgi, by vesicle trafficking. From the golgi, proteins are packaged into vesicles. It is a hotly debated topic whether proteins are sorted into specific vesicles or proteins within vesicles (that do not belong in that vesicle) are sorted away (and degraded by the lysosome).

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.