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Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Ribosomes are responsible for synthesizing proteins and forming amino acids. This process is also known as translation and occurs after DNA replication and transcription. Ribosomes read as they move along the messenger RNA template that is used to copy a particular DNA sequence and produce an amino acid chain.

One of the most basic processes of a cell is protein synthesis and the key organelle for that is the ribosome. It's what physically actually puts amino acids together to form the long chains of a protein. Now, where is it located? It's floating around inside of the cell. If we take a look at this cell here, you can see there is a bunch of little ribosomes floating around the cytoplasm there's also a whole bunch of them studded up against the membrane of the rough endoplasmic reticulum in fact it's the ribosomes that give the rough texture to the rough ER, so what does it do? Well if we take a look here we can se that it's following the instructions here of a messenger RNA molecule that came out of the nucleus, so the ribosomes are the puppet of DNA and the RNA carries that message to the ribosomes for it to follow.

Now when we look at this structure here, we see this red thing here which I've already identified it as the messenger RNA. This blue thing with its little amino acid and the thiamine attached to it, that's the transfer RNA. The two orange substances are the two parts or subunits of a ribosome. Now you may be wondering, what do we call these two subunits? Well scientists looked at it and said, "well this one is bigger let's call it the large subunit, this wee little one let's call the small subunit" cause I guess they weren't Scottish. So the most ribosomes have two subunits the large subunit and small subunit now I discussed and I hesitated there when I was talking about the ribosomes cause actually there's two different kinds of ribosomes.

There are the ribosomes found in prokaryotes like bacteria and their large subunits is just little bit smaller than the large subunit of eukaryotic cells like myself. We have a nucleus and our large subunit is larger than the large subunit of prokaryotes. Similarly, the subunit, the small subunit of prokaryotes is little bit smaller than the small subunit of eukaryotic cells.

Now messenger RNA you might be able to guess is made out of RNA, TRNA is transfer RNA it too is made out of RNA can you guess what kind of molecule makes up the bulk of ribosomes? Yes, you've got it! its RRNA which stands for ribosomal RNA. There's a few other proteins that working together with the ribosomal or RNA help catalyze the addition of amino acids to each other giving us the structure and function of a ribosome.