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Wize Grade 12 Biology Textbook > Cell Components: Structure and Function

Ribosomes

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Ribosomes

Ribosomes are small, bead-like structures that play an important role in protein synthesis. Since they are not bound by a membrane, they are not considered to be organelles, and can be found abundantly in both eukaryotic and prokaryotic cells.

adapted from Science Primer (National Center for Biotechnology Information) / CC BY
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Location

Ribosomes can be located either freely floating within the cytosol, or bound to the membrane of the rough endoplasmic reticulum or nuclear envelope.

adapted from Mariana Ruiz / CC BY

  • The location of ribosomes in the cell determines the location of the proteins that they synthesize.
  • Freely floating ribosomes will synthesize proteins that will be used
    in
    side the cell, within the cytoplasm.
  • Membrane bound ribosomes (bound to the rough endoplasmic reticulum) will synthesize proteins that will be used
    out
    side of the cell or inserted within the cell membrane or organelle membranes.
  • Cells that have high rates of protein synthesis will have a large number of ribosomes, and a prominent nucleoli.
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Structure

All ribosomes consist of 2 major parts; the small and large ribosomal subunits. Both subunits are composed of ribosomal proteins (RBs) and ribosomal RNA (rRNA) molecules.


adapted from Vossman / CC BY
  • The structure of eukaryotic and prokaryotic ribosomes are very similar; however, eukaryotic ribosomes are slightly larger.
  • The molecular composition of eukaryotic and prokaryotic ribosomes are quite different. These differences are of significance for medicinal purposes.
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Function

Ribosomes help in the synthesis of proteins in a process called translation, that's way they are nicknamed the "protein factory." During translation ribosomes will read strands of messenger RNA (mRNA) and bring the correct amino acids together to form a polypeptide chain that will eventually become a functional protein.

adapted from CNX OpenStax / CC BY

Practice: Ribosome Structure and Function

What is the location of ribosomes that synthesize proteins to be embedded within the cell membrane?

Practice: Ribosome Structure

Each ribosomal subunit consists of which of the following?