Ribosome — Structure & Function

What Is a Ribosome?

Ribosomes are responsible for building proteins for the cell. The fancier way of saying this is that they carry out the process of protein synthesis.

The actual process in which these organelles synthesize proteins is called translation. We'll cover this in its own section because it's super important.

A ribosome itself looks like a little hamburger bun. It's made of two subunits: a big one (the top bun) and a small one (the bottom bun).

Ribosomes are made in the nucleolus, a cluster of proteins and RNA found in the center of a cell's nucleus. They are actually assembled from a special type of RNA, ribosomal RNA (rRNA). You'll find them in all eukaryotic cells (plants and animals) and in prokaryotes.

I repeat: prokaryotes (like bacteria) do have this organelle. So its presence in a cell will not help you determine what kind of cell it is. Everybody's got 'em.

Eukaryotic ribosomes are found floating freely in the cytoplasm or attached to the rough endoplasmic reticulum (RER or rough ER for short).

Since prokaryotes, like bacteria, don't have endoplasmic reticulums, prokaryotic ribosomes can be found just floating around the cytoplasm.

There can be anywhere from a few all the way up to ten million ribosomes in just one cell. Obviously, cells that require more proteins will likely have more ribosomes than those that need fewer proteins.

Key Vocabulary:

1. Ribosome
2. Subunit
3. Protein
4. Nucleolus
5. Translation
6. Protein synthesis

Much like how the mitochondria are the powerhouse of the cell, ribosomes are the protein factory of the cell. They are made of two pieces: the large subunit and the small subunit.

These little guys are made by the nucleolus, which is part of the cell nucleus. They are made from a specific type of RNA, the ribosomal RNA (or rRNA). They carry out translation to help with creating proteins. Translation is basically using the genetic code of DNA to create a polypeptide chain of amino acids. This chain increases in length until a protein is made. The main helpers in translation are messenger RNA (mRNA) molecules and transfer RNA (tRNA) molecules.

Ribosomes are found in both prokaryotic and eukaryotic cells. In eukaryotic cells they are located on the rough endoplasmic reticulum, or RER for short. There are also some floating free in the cytoplasm of the cell. In prokaryotic cells, this organelle can only be found in the cytoplasm because prokaryotes do not have an endoplasmic reticulum.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Vacuole}}$ : Organelle that contains water and nutrients. Refrigerator of the cell

$\color{#8925AE}{\text{Golgi Apparatus}}$ : Stores, sorts, and modifies proteins and lipids. Post office of the cell

$\color{#8925AE}{\text{Cytoskeleton}}$ : Helps the cell maintain its shape and assists with movement. Skeleton of the cell

$\color{#8925AE}{\text{Mitochondria}}$ : Makes ATP (energy). Powerhouse of the cell

$\color{#8925AE}{\text{Ribosome}}$ : Creates polypeptide chains and proteins. Factory of the cell

$\color{#8925AE}{\text{Endoplasmic Reticulum}}$ : The smooth ER makes lipids for the cellular membrane. The rough ER assembles proteins and transports them into and out of the cell.

$\color{#8925AE}{\text{Nucleus}}$ : Contains the genetic material, DNA, of the cell. Brain of the cell

(Video) Cells - Ribosomes

by Mahalo

This video will give you a brief introduction to ribosomes, including their functions and where they are found.