Ribosomes are non-membranous bounded strOctures. Ribosomes are the sites where the cell synthesizes proteins according to genetic instructions. A bacterial cell may have a few thousand ribosomes.But a human liver cell has a few million ribosomes. Cells hat have high protein synthesis have a particulaly great number of ribosome. Cells active in protein synthesis also have prominent nucleoli.These nucleoli synthesize the ribosomes.


Chemical composition

They colitain equal amount of proteins and rRNA So they are also known as

Types of ribosomes

Ribosornes function in two cytoplasmic locations.

  • Free ribosomes: They are suspended in the cytoplasm. Most of proteins synthesized by the free ribosomes will function within the cytosol. The free ribosomes are abundant in the cells growing by the addition of cytoplasm.
  • Bound ribosomes: They are attached to the outside of the endoplasmic

reticulum. The proteins of bound ribosomes are stored in the inclusion of mem manes. Or these proteins are exported from the cell. Some cells specialize in protein secretion like pancreas and other glands. These cells secrete digestive enzymes. They have a high proportion of bound ribosomes.

Structure of ribosomes

Bound and free ribosomes are structurally identical and interchangeable. The cells car adjust the numbers of ribosome. Each ribosome has two subunits. The ribosomal subunits are constructed in the nucleolus from RNA in eukaryotes. The rRNA is produced in the nucleus. Protein is imported from the cytoplasm. The subunits join to form functional ribosomes.

Functions of ribosomes

The ribosome plays a key role in translating the genetic message. This genetic message is carried by mRNA from the nucleus to the cytoplasm. This message sequence) of a.polypeptide chain.

The ribosomes of prokaryotes are smaller than eukaryotes. They are different in their molecular composition. This dissimilarity in a structure is fundamental. It differentiates the prokaryotes from eukaryotes. The difference in ribosomes is also medically significant. Certain drugs (antibiotics) can affect the prokaryotic ribosomes. But they do not affect the eukaryotic ribosomes.


Complete protein


Component Structure /Description Function
Centriole Located      within        microtubule-



organizing        center.       Contains
nine triple microtubules

Forms basal body of cilia an

flagella;    functions      in   mitotii
spindle formation

Chloroplast Organelle           that           contains

chlorophyll    and  is    involved    in

Traps, transforms,         and    use

tight energy -to convert carbor dioxide and water into glucose and oxygen

Chromosome Made up of nucleic acid (DNA) and protein Controls heredity- and pellula activities
Cilia, flagella Thread like structures Cilia and flagella move smal

particles      through     fixed   cellE

and     are     a    major     form    o.
locomotion in some cells.

Cytomembrane system The      endoplasmic       reticulum,

Golgi apparatus,, vacuoles, vesicles


Organelles     functioning    as     a

system,     to  modify,     package.

and     distribute     newly    formec
proteins and lipids








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