Quick biology question

proteins are synthesised by ribosomes, but these can be attached to the RER

Yes it would be wrong, just like saying protein is synthesised in the cell It's the ribosomes my friend.

I think the RER concentrates and modifies the proteins.

Isn't that what the Golgi apparatus does.

So what the hell does RER do.

The way i understand the basics of it all is that the ribosomes on the membrane of the RER make the proteins and pass them into the RER, the RER processes the proteins and folds them into their required shape and them secrete them, using their membranes to create a bubble around the protein, i.e. a vesicle. The vesicles are then transported to to the golgi apparatus where bits and bobs get added to the protein (e.g. carbs, other proteins and inorganic molecules).

Ribosomes - make proteins
RER - Folds proteins
Golgi apparatus - adds to proteins

is protein synthesised in ribosomes or rer

I'm glad you did this question, I would have went strolling into the exam think it is the RER

How do the free ribosomes get folded?

I think it is dependant on the sequence of amino acids
not sure though

So would ribosomes which are free make proteins for the actual cell itself but the ones on the RER make proteins to be used elsewhere.

Pretty much. Ribosomes are the site of protein synthesis. If a protein needs to be secreted from the cell, then a signal sequence in the protein causes the ribosome to move to the RER. The protein enters the RER, is modified and passed on to the Golgi for secretion.