The Ribosome: Structure, Function and Location

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  • 1:18 Ribosomes
  • 2:50 Ribosome Structure
  • 4:33 Lesson Summary
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Lesson Transcript
Instructor: Kristin Klucevsek

Kristin has taught college Biology courses and has her doctorate in Biology.

The ribosome is the cellular structure responsible for decoding your DNA. In this lesson, we'll learn about ribosome structure, function and location - characteristics that make it a very good genetic translator.

Ribosomes Perform Protein Synthesis

The central dogma of biology and the types of RNA
Central Dogma Visual

We've reached a point in science where it's possible to find out all the letters in your DNA sequence, and that's pretty cool. But if you've ever looked at a DNA sequence, you might have noticed it isn't exactly English. We can find out all the As, the Gs, the Ts and the Cs in a human genome, but it's a completely different language than the one you likely learned in grade school. How can you tell which of these letters made your eyes blue and which ones gave you those big ears?

Fortunately, your cells can read your genome language just fine, though it takes a few steps. Your DNA tells your cells what proteins to make. Remember that it does this through the central dogma, where your DNA is first transcribed into RNA. DNA is a huge manual of instructions, so transcription is like writing down one page of DNA instructions at a time. There are three types of RNA made during transcription - messenger RNA (or mRNA), transfer RNA (or tRNA) and ribosomal RNA (or rRNA). In the second step of the central dogma, mRNA is translated into protein during translation. You'll remember that proteins are built from several different amino acids in a specific order.

So, after that refresher, it's time to introduce you to the smarty-pants of the cell who is able to speak this DNA language. This would be the ribosome, the cellular structure that performs translation, or protein synthesis. Ribosomes are both language translators and efficient assembly workers. Putting together any sort of protein is like putting together a piece of furniture that has three boxes of more than 100 parts - and the instructions are in a foreign language, with no pictures. We've all tried to do it, and it's not pretty. But for ribosomes, this is a cinch. They read an mRNA sequence, translate it and use tools to build it into a protein. This protein is then used by the cell. Specifically, ribosomes use tRNA as tools. This helps bring the correct amino acids to the building protein.

The location of free and bound ribosomes in cells
Ribosome Type Diagram

Ribosomes are composed of rRNA and proteins. They exist free in the cytoplasm until they receive an mRNA message to translate. When they receive it, they waste no time in cracking the code. Ribosomes can either be free ribosomes in the cytoplasm of the cell or they may find that the mRNA they are translating has a specific destination. In this case, some ribosomes will attach themselves to another cellular structure, and this is called the endoplasmic reticulum. Here, these are called the bound ribosomes. Proteins produced by bound ribosomes are usually destined for some kind of specific structures, or they're meant to exit the cell through exocytosis. There are also ribosomes within the mitochondria and chloroplasts of different types of cells, but we'll discuss that in other lessons.

Ribosome Structure

Although different organisms might have slightly different-sized ribosomes, they are very similar in the structure and all perform translation. Specifically, translation is protein synthesis by creating a chain of amino acids linked together by polypeptide bonds.

Ribosomes are composed of two different subunits, called the large subunit and the small subunit. Both subunits are composed of rRNA and protein. These subunits usually exist separately in the cytoplasm until the small subunit recognizes and binds to a specific sequence of an mRNA message. It then recruits the large subunit to form a complete ribosome.

The structure of ribosomes
Ribosome Structure

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