| Membrane proteins and glycolipids mediate cell | | | | to be the smallest cellular organelles. Each ribosome is |
| recognition events, which are seen in certain | | | | composed of several different ribosomal RNA |
| contexts such as immune responses. The plasma | | | | (rRNA) molecules and more than 50 proteins, |
| membrane also mediates the flow of information to | | | | organized into a large subunit and a small subunit. |
| the cell in the form of messenger molecules such as | | | | Ribosomes are present in three places in almost all |
| hormones, a process known as signal transduction. | | | | eukaryotic cells: free in the cytoplasm, attached to |
| Here, the binding of the signalling molecule to specific | | | | the surface of the endoplasmic reticulum, and |
| receptor proteins triggers off a series of enzymatic | | | | contained in the endoplasmic reticulum. In plant cells, |
| reactions in the plasma membrane, leading to an | | | | ribosomes are also present in chloroplasts. When not |
| appropriate response by the cell. The entire part of | | | | active in the synthesis of proteins, the ribosomes |
| the cell inside the plasma membrane (excluding the | | | | exist as separate subunits. The process of |
| nucleus in eukaryotes) constitutes the cytoplasm. | | | | synthesizing a polypeptide using the information |
| The bulk of vital metabolic processes in the cell | | | | contained in an mRNA is called translation. A ribosome |
| occurs within the cytoplasm. The cytoplasm of | | | | can take part in the translation of any mRNA to |
| prokaryotes consists of a watery medium called the | | | | make different polypeptide products. Each individual |
| cytosol and suspended insoluble particles. In | | | | amino acid is associated with a RNA molecule called |
| eukaryotes, the cytoplasm consists of the cytosol | | | | the transfer RNA (tRNA). While the information |
| and various organelles. The cytosol contains dissolved | | | | required to synthesize the polypeptide is present in |
| ions, small molecules, and soluble macromolecules such | | | | the mRNA and the constituent amino acids are borne |
| as enzymes. The insoluble particles in the cytoplasm | | | | by the tRNA, the ribosome is simply the molecular |
| include the ribosomes, which form the | | | | machinery that accomplishes the task. Its structure |
| protein-synthesizing machinery. Ribosomes are | | | | enables it to hold the mRNA and the tRNAs in the |
| protein synthesizing machines that associate | | | | right positions, thus allowing the growing polypeptide |
| with messenger RNA (mRNA) and catalyze the | | | | to be assembled efficiently. |
| synthesis of proteins. Ribosomes can be considered | | | | |