The endoplasmic reticulum is an important organelle that makes up 10% of the cell's volume. The endoplasmic reticulum, or ER, surounds the nucleus and spreads through out the cell. There are two types of ER: smooth and rough. The smooth ER contains no ribosomes on its membrane, hence the name "smooth". This smooth structure is because the main purpose of the smooth ER is to synthesize lipids and decrease toxicity of the cell. In contrast the rough ER has ribosomes scattered along the membrane because the main purpose of the rough ER is to synthesize, process, and export protiens. In terms of the relationship of the ER to ribosomes, a ribosome will recgonize a translation initation sequence of an mRNA and begin synthesizing the protein. This complex will then bind a translocon located on the membrane of the ER. This channel protein will direct the newly synthesized protein into the lumen of the ER. The protein is then processed and can possibly be retained in the lumen, secreted into the cytoplasm, or released in a vesicle.
Comments
wording
There are a couple spelling errors "surrounds" missing an r in the second sentence and "protein" the i and e are switched in the end of sentence 6. A little nit-picky by me but good paragraph.
wording
"This smooth structure is because..." has awkard wording. Maybe if you don't mention the smooth structure at all, the sentence would be better. The next sentence highlights the function of the subject at hand, so there's no need to mention the structure unless you are making an explicit comparison
Sentences
You should combine some of your sentences together to make the paragraph sound smoother. For example combining the sentences about the ribosomes on the rough ER would make the paragraph flow better.