Ribosomes Function | What are Ribosomes | Types of Ribosomes | Ribosomes Function

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Ribosomes Definition

Ribosomes are small granules of RNAs responsible for the production of protein synthesis. The ribosomes of a cell may be freely scattered in a cell cytosol or may be bound to the surface of the rough Endoplasmic Reticulum.

What are Ribosomes

Ribosomes are small spherical and granular organelles bounded by double layered membrane. Bound and free ribosomes are structurally identical and interchangeable and the cell can adjust the relative number of each as its metabolism changes. Both types of ribosomes usually occur in clusters called polyribosomes that are attached to one mRNA molecule, an arrangement that increases the rate of polypeptide synthesis.

The ribosomes of eukaryotic cells and prokaryotic cells are entirely dissimilar this is the reason why some drugs like tetracycline and streptomycin can select and inhibit protein synthesis of only bacteria and not that of the host cell.

Where are Ribosomes found?

Ribosomes are found in the cytosol of plant and animal cells. The free ribosomes are scattered in the cytosol while the bound ribosomes are attached to the rough endoplasmic.

What is the function of Ribosomes

Ribosomes are the sites of Protein synthesis of both plant and animal cells. There two types of Ribosomes: which are the free Ribosomes and the bound Ribosomes. The free ribosomes synthesize cytoskeletal proteins and other cytoplasmic proteins such as hemoglobin. The proteins synthesized by free ribosomes also find their way into the nucleus, mitochondria, and peroxisomes. The bound ribosomes are located on the rough Endoplasmic reticulum and are responsible for the synthesis of all membrane proteins and most of the secreted proteins. The proteins synthesized by bound ribosomes are extruded into the rough Endoplasmic reticulum.

What do Ribosomes do? (Ribosomes Functions)

  1. Ribosomes are involved in protein folding
  2. Ribosomes are called protein factories because of their role in the synthesis of proteins.
  3. Messenger RNA (mRNA) carries the genetic code for protein synthesis from nucleus to the ribosomes. The ribosomes, in turn arrange the amino acids into small units of proteins.
  4. Ribosomes attached to rough endoplasmic reticulum are involved in the synthesis of proteins such as the enzymatic proteins, hormonal proteins, lysosomal proteins and the proteins of the cell membrane.
  5. Free ribosomes are responsible for the synthesis of proteins in hemoglobin, peroxisome and mitochondria.

Types of Ribosomes

Ribosomes are of two types:

  1. Ribosomes that are attached to rough endoplasmic reticulum
  2. Free ribosomes that are distributed in the cytoplasm.

Ribosomes Diagram

Diagram showing free Ribosomes scattered in the cytosol of a cell
Diagram showing free Ribosomes scattered in the cytosol of a cell


Ribosomes Structure

Ribosomes are small organelles measuring averagely about 25 nanometer in diameter. They are dense granules composed of rRNA and proteins that function in protein synthesis.

Each ribosome consists of a small subunit (30S) and a large subunit (50S) that are separate and located in the cytosol when the ribosome is not active. During protein synthesis the two sub-units come together in the cytosol to form a functional ribosome.

After protein synthesis is initiated, some ribosomes remain free in the cytosol, whereas others become attached to the rough endoplasmic reticulum.

Proteins synthesized in association with free ribosomes can remain in the cytosol or enter a mitochondrion, the nucleus, or a peroxisome. Proteins synthesized in association with the rough endoplasmic reticulum will be packaged into vesicles by the Golgi apparatus and directed to their ultimate destination.

Ribosomal RNA

Ribosomes are made up of 35% of proteins and 65% of ribonucleic acid (RNA). RNA present in ribosomes is called ribosomal RNA (rRNA). Ribosomes are concerned with protein synthesis in the cell.

Where are Ribosomes Found

Ribosomes are found scattered in the cytosol of the cytoplasm (these are known as Free Ribosomes) or they may be attached to the outer wall of rough endoplasmic reticulum (Bound Ribosomes).