Transcribed cytoplasm
tRNA
Ribosomes are located in the cytoplasm, the fluid material that comprises the cell. In prokaryotes, ribosomes freely float in the cytoplasm. In eukaryotes, ribosomes can be both freely floating and membrane-bound. The ribosome's role in gene expression is to synthesize proteins based on the instructions provided by mRNA. The mRNA strand is made from the cell's DNA and tells the ribosome how to construct the cell's necessary proteins.
The ribosome is essential for protein synthesis, so it is part of translation and not transcription. The ribosome reads instructions from mRNA and "translates" them into proteins.
Prokaryotes and eukaryotes have some major structural differences, so the details of protein synthesis differ between these two types of organisms as well. Prokaryotic organisms such as bacteria do not have a cell nucleus, so the cell's DNA floats freely in the cell. In eukaryotic organisms such as humans, the cell's DNA is located in the nucleus, while the ribosome is located in the cytoplasm.
Eukaryotic ribosomes are also larger and more complex than prokaryotic ribosomes.
Transfer RNA, or tRNA, provides a physical link between the codons of the mRNA and the amino acids to be added to the polypeptide chain. Specific tRNA molecules are bound to specific amino acids, and tRNA that is complementary to the mRNA codon enters the ribosome and transfers its amino acid to the growing polypeptide chain.
Ribosomal RNA, or rRNA, is an important component of the ribosome. Both eukaryotic and prokaryotic ribosomes contain rRNA. rRNA and proteins together carry out the functions of the ribosome.
If there are no ribosomes present in the cell, proteins cannot be made. Without protein synthesis, cells cannot accomplish their necessary functions, and the organism will die.